Patent Publication Number: US-10789202-B2

Title: Image processor with configurable number of active cores and supporting internal network

Description:
FIELD OF INVENTION 
     The field of invention pertains generally to the computing sciences and, more specifically, to an image processor with a configurable number of active cores and a supporting internal network. 
     BACKGROUND 
     Image processing typically involves the processing of pixel values that are organized into an array. Here, a spatially organized two dimensional array captures the two dimensional nature of images (additional dimensions may include time (e.g., a sequence of two dimensional images) and data type (e.g., colors). In a typical scenario, the arrayed pixel values are provided by a camera that has generated a still image or a sequence of frames to capture images of motion. Traditional image processors typically fall on either side of two extremes. 
     A first extreme performs image processing tasks as software programs executing on a general purpose processor or general purpose-like processor (e.g., a general purpose processor with vector instruction enhancements). Although the first extreme typically provides a highly versatile application software development platform, its use of finer grained data structures combined with the associated overhead (e.g., instruction fetch and decode, handling of on-chip and off-chip data, speculative execution) ultimately results in larger amounts of energy being consumed per unit of data during execution of the program code. 
     A second, opposite extreme applies fixed function hardwired circuitry to much larger units of data. The use of larger (as opposed to finer grained) units of data applied directly to custom designed circuits greatly reduces power consumption per unit of data. However, the use of custom designed fixed function circuitry generally results in a limited set of tasks that the processor is able to perform. As such, the widely versatile programming environment (that is associated with the first extreme) is lacking in the second extreme. 
     A technology platform that provides for both highly versatile application software development opportunities combined with improved power efficiency per unit of data remains a desirable yet missing solution. 
     SUMMARY 
     A method is described. The method includes configuring a first instance of object code to execute on a processor. The processor has multiple cores and an internal network. The internal network is configured in a first configuration that enables a first number of the cores to be communicatively coupled. The method also includes configuring a second instance of the object code to execute on a second instance of the processor. A respective internal network of the second instance of the processor is configured in a second configuration that enables a different number of cores to be communicatively coupled, wherein, same positioned cores on the processor and the second instance of the processor have same network addresses for the first and second configurations. A processor is also described having an internal network designed to enable the above method. 
    
    
     
       FIGURES 
       The following description and accompanying drawings are used to illustrate embodiments of the invention. In the drawings: 
         FIG. 1  shows a high level view of a stencil processor architecture; 
         FIG. 2  shows a more detailed view of an image processor architecture; 
         FIG. 3  shows an even more detailed view of an image processor architecture; 
         FIG. 4  shows an application software program that can be executed by an image processor; 
         FIG. 5  shows the image processor of  FIG. 3  with the network ring configured to support a configurable number of active cores; 
         FIGS. 6 a , 6 b , 6 c  and 6 d    show the image processor of  FIG. 5  configured with different numbers of active cores; 
         FIG. 7  shows a processor configuration method; 
         FIGS. 8 a , 8 b , 8 c , 8 d  and 8 e    depict the parsing of image data into a line group, the parsing of a line group into a sheet and the operation performed on a sheet with overlapping stencils; 
         FIG. 9 a    shows an embodiment of a stencil processor; 
         FIG. 9 b    shows an embodiment of an instruction word of the stencil processor; 
         FIG. 10  shows an embodiment of a data computation unit within a stencil processor; 
         FIGS. 11 a , 11 b , 11 c , 11 d , 11 e , 11 f , 11 g , 11 h , 11 i , 11 j  and 11 k    depict an example of the use of a two-dimensional shift array and an execution lane array to determine a pair of neighboring output pixel values with overlapping stencils; 
         FIG. 12  shows an embodiment of a unit cell for an integrated execution lane array and two-dimensional shift array; 
         FIG. 13  shows an exemplary computing system. 
     
    
    
     DETAILED DESCRIPTION 
     1.0 Unique Image Processor Architecture 
     As is known in the art, the fundamental circuit structure for executing program code includes an execution stage and register space. The execution stage contains the execution units for executing instructions. Input operands for an instruction to be executed are provided to the execution stage from the register space. The resultant that is generated from the execution stage&#39;s execution of an instruction is written back to the register space. 
     Execution of a software thread on a traditional processor entails sequential execution of a series of instructions through the execution stage. Most commonly, the operations are “scalar” in the sense that a single resultant is generated from a single input operand set. However in the case of “vector” processors, the execution of an instruction by the execution stage will generate a vector of resultants from a vector of input operands. 
       FIG. 1  shows a high level view of a unique image processor architecture  100  that includes an array of execution lanes  101  coupled to a two-dimensional shift register array  102 . Here, each execution lane in the execution lane array can be viewed as a discrete execution stage that contains the execution units needed to execute the instruction set supported by the processor  100 . In various embodiments each execution lane receives a same instruction to execute in a same machine cycle so that the processor operates as a two dimensional single instruction multiple data (SIMD) processor. 
     Each execution lane has its own dedicated register space in a corresponding location within the two dimensional shift register array  102 . For example, corner execution lane  103  has its own dedicated register space in corner shift register location  104 , corner execution lane  105  has its own dedicated register space in corner shift register location  106 , etc. 
     Additionally, the shift register array  102  is able to shift its contents so that each execution lane is able to directly operate, from its own register space, upon a value that was resident in another execution lane&#39;s register space during a prior machine cycle. For example, a +1 horizontal shift causes each execution lane&#39;s register space to receive a value from its leftmost neighbor&#39;s register space. On account of an ability to shift values in both left and right directions along a horizontal axis, and shift values in both up and down directions along a vertical axis, the processor is able to efficiently process stencils of image data. 
     Here, as is known the art, a stencil is a slice of image surface area that is used as a fundamental data unit. For example, a new value for a particular pixel location in an output image may be calculated as an average of the pixel values in an area of an input image that the particular pixel location is centered within. For example, if the stencil has a dimension of 3 pixels by 3 pixels, the particular pixel location may correspond to the middle pixel of the 3×3 pixel array and the average may be calculated over all nine pixels within the 3×3 pixel array. 
     According to various operational embodiments of the processor  100  of  FIG. 1 , each execution lane of the execution lane array  101  is responsible for calculating a pixel value for a particular location in an output image. Thus, continuing with the 3×3 stencil averaging example mentioned just above, after an initial loading of input pixel data and a coordinated shift sequence of eight shift operations within the shift register, each execution lane in the execution lane array will have received into its local register space all nine pixel values needed to calculate the average for its corresponding pixel location. That is, the processor is able to simultaneously process multiple overlapping stencils centered at, e.g., neighboring output image pixel locations. Because the processor architecture of  FIG. 1  is particularly adept at processing over image stencils it may also be referred to as a stencil processor. 
       FIG. 2  shows an embodiment of an architecture  200  for an image processor having multiple stencil processors  202 _ 1  through  202 _N. As observed in  FIG. 2 , the architecture  200  includes a plurality of line buffer units  201 _ 1  through  201 _M interconnected to a plurality of stencil processor units  202 _ 1  through  202 _N and corresponding sheet generator units  203 _ 1  through  203 _N through a network  204  (e.g., a network on chip (NOC) including an on chip switch network, an on chip ring network or other kind of network). In an embodiment, any line buffer unit  201 _ 1  through  201 _M may connect to any sheet generator  203 _ 1  through  203 _N and corresponding stencil processor  202 _ 1  through  202 _N through the network  204 . 
     Program code is compiled and loaded onto a corresponding stencil processor  202  to perform the image processing operations earlier defined by a software developer (program code may also be loaded onto the stencil processor&#39;s associated sheet generator  203 , e.g., depending on design and implementation). As such, each stencil processor  202 _ 1  through  202 _N may be more generally characterized as a processing core, processor core, core and the like and the overall image processor may be characterized as a multi-core image processor. In at least some instances an image processing pipeline may be realized by loading a first kernel program for a first pipeline stage into a first stencil processor  202 _ 1 , loading a second kernel program for a second pipeline stage into a second stencil processor  202 _ 2 , etc. where the first kernel performs the functions of the first stage of the pipeline, the second kernel performs the functions of the second stage of the pipeline, etc. and additional control flow methods are installed to pass output image data from one stage of the pipeline to the next stage of the pipeline. 
     In other configurations, the image processor may be realized as a parallel machine having two or more stencil processors  202 _ 1 ,  202 _ 2  operating the same kernel program code. For example, a highly dense and high data rate stream of image data may be processed by spreading frames across multiple stencil processors each of which perform the same function. 
     In yet other configurations, essentially any directed acyclic graph (DAG) of kernels may be loaded onto the image processor by configuring respective stencil processors with their own respective kernel of program code and configuring appropriate control flow hooks into the hardware to direct output images from one kernel to the input of a next kernel in the DAG design. 
     As a general flow, frames of image data are received by a macro I/O unit  205  and passed to one or more of the line buffer units  201  on a frame by frame basis. A particular line buffer unit parses its frame of image data into a smaller region of image data, referred to as a “line group”, and then passes the line group through the network  204  to a particular sheet generator. A complete or “full” singular line group may be composed, for example, with the data of multiple contiguous complete rows or columns of a frame (for simplicity the present specification will mainly refer to contiguous rows). The sheet generator further parses the line group of image data into a smaller region of image data, referred to as a “sheet”, and presents the sheet to its corresponding stencil processor. 
     In the case of an image processing pipeline or a DAG flow having a single input, generally, input frames are directed to the same line buffer unit  201 _ 1  which parses the image data into line groups and directs the line groups to the sheet generator  203 _ 1  whose corresponding stencil processor  202 _ 1  is executing the code of the first kernel in the pipeline/DAG. Upon completion of operations by the stencil processor  202 _ 1  on the line groups it processes, the sheet generator  203 _ 1  sends output line groups to a “downstream” line buffer unit  201 _ 2  (in some use cases the output line group may be sent back to the same line buffer unit  201 _ 1  that earlier had sent the input line groups). 
     One or more “consumer” kernels that represent the next stage/operation in the pipeline/DAG executing on their own respective other sheet generator and stencil processor (e.g., sheet generator  203 _ 2  and stencil processor  202 _ 2 ) then receive from the downstream line buffer unit  201 _ 2  the image data generated by the first stencil processor  202 _ 1 . In this manner, a “producer” kernel operating on a first stencil processor has its output data forwarded to a “consumer” kernel operating on a second stencil processor where the consumer kernel performs the next set of tasks after the producer kernel consistent with the design of the overall pipeline or DAG. 
     As alluded to above with respect to  FIG. 1 , each stencil processor  202 _ 1  through  202 _N is designed to simultaneously operate on multiple overlapping stencils of image data. The multiple overlapping stencils and internal hardware processing capacity of the stencil processor effectively determines the size of a sheet. Again, as discussed above, within any of stencil processors  202 _ 1  through  202 _N, arrays of execution lanes operate in unison to simultaneously process the image data surface area covered by the multiple overlapping stencils. 
     Additionally, in various embodiments, sheets of image data are loaded into the two-dimensional shift register array of a stencil processor  202  by that stencil processor&#39;s corresponding (e.g., local) sheet generator  203 . The use of sheets and the two-dimensional shift register array structure is believed to effectively provide for power consumption improvements by moving a large amount of data into a large amount of register space as, e.g., a single load operation with processing tasks performed directly on the data immediately thereafter by an execution lane array. Additionally, the use of an execution lane array and corresponding register array provide for different stencil sizes that are easily programmable/configurable. More details concerning the operation of the line buffer units, sheet generators and stencil processors are provided further below in Section 3.0. 
       FIG. 3  shows a more detailed embodiment of a specific hardware implementation of the image processor of  FIG. 2 . As observed in  FIG. 3 , the network  204  of  FIG. 2  is implemented in a ring topology  304  with a 4×4 network node  314  at each intersection between a line buffer unit  301  and sheet generator/stencil processor core  302 . For simplicity,  FIG. 3  only labels the network node  314  that resides between line buffer unit  301 _ 4  and sheet generator/stencil processor core  302 _ 4 . 
     Here, each of sheet generator/stencil processor cores  302 _ 1  through  302 _ 8  are understood to include both a stencil processor and its corresponding sheet generator. For simplicity, each of the sheet generator/stencil processor cores  302 _ 1  through  302 _ 8  will hereinafter be referred to simply as a stencil processor core or core. Although eight line buffer units  301 _ 1  through  301 _ 8  and eight cores  302 _ 1  through  402 _ 8  are depicted in the particular embodiment of  FIG. 3  it should be understood that different architectures are possible having different numbers of line buffer units and/or cores. Network topologies other than a ring topology are also possible. 
     With respect to the image processor of  FIG. 3 , the ring network  304  permits: 1) the I/O unit  305  to pass input data to any line buffer unit  301 _ 1  through  301 _ 8  (or any core  302 _ 1  through  302 _ 8 ); 2) any line buffer unit  301 _ 1  to  301 _ 8  to forward a line group to any core  302 _ 1  through  302 _ 8 ; 3) any core  302 _ 1  through  302 _ 8  to pass its output data to any line buffer unit  301 _ 1  through  301 _ 8 ; and, 4) any line buffer unit  301 _ 1  through  301 _ 8  to pass image processor output data to I/O unit  305 . As such, a wealth of different software kernel loading options and internal network configurations are possible. That is, theoretically, for any software application composed of multiple kernels to be executed on the various cores  302  of the processor, any kernel can be loaded onto any core and any line buffer unit can be configured to source/sink input/output data to/from any core. 
       FIG. 4  shows an exemplary application software program  400  or portion thereof that may be loaded onto the image processor of  FIG. 3 . As observed in  FIG. 4 , the program code may be expected to process one or more frames of input image data  401  to effect some overall transformation on the input image data  401 . The transformation is realized with the operation of one or more kernels of program code  402  that operate on the input image data in an orchestrated sequence articulated by the application software developer. 
     In the example of  FIG. 4 , the overall transformation is effected by first processing each input image with a first kernel K 1 . The output images produced by kernel K 1  are then operated on by kernel K 2 . Each of the output images produced by kernel K 2  are then operated on by kernel K 3 _ 1  or K 3 _ 2 , The output images produced by kernel(s) K 3 _ 1 /K 3 _ 2  are then operated on by kernel K 4 . In the particular example of  FIG. 3 , Kernels K 3 _ 1  and K 3 _ 2  may be, e.g., different kernels that perform different image processing operations (e.g., kernel K 3 _ 1  operates on input images of a first specific type and kernel K 3 _ 2  operates on input images of a second, different type). 
     For simplicity only four kernels K 1  through K 4  are shown. In reference to the image processor hardware architecture embodiment of  FIG. 3 , note that, in a basic configuration where each kernel operates on a different stencil processor, conceivably, four more kernels may flow from kernel K 4  before all the cores  302  of the processor have a corresponding kernel (the four kernel flow of  FIG. 4  only utilizes half the cores of the processor of  FIG. 3 ). 
     2.0 Image Processor with Configurable Number of Cores and Supporting Internal Network 
       FIG. 5  shows an embodiment  500  of the image processor of  FIG. 3  with a more detailed view of the ring network implementation and the specific addresses that are assigned to each node on the network ring. As observed in  FIG. 5 , the ring network includes multiplexer pairs  506 _ 1 ,  506 _ 2  and  506 _ 3  to enable different numbers of the processor&#39;s cores  502 _ 1  through  502 _ 8 . Also shown are line buffer units  501 _ 1  to  501 _ 8 . Here, the image processor  500  may include configuration register space (not shown in  FIG. 5 ) that, e.g., determines channel select values of the multiplexers so as to put into effect or otherwise implement any particular one of a number of different network configurations (such as any/all of the configurations discussed below). As observed in  FIG. 5 , if the A channel of a multiplexer pair is selected, the ring continues forward to connect a next pair of processor cores. By contrast, if the B channel of a multiplexer pair is selected, the ring “short circuits” so as to cut off the next pair of processor cores. 
       FIGS. 6 a  through 6 d    show the different ring network and number of active processor core configurations that are possible with the image processor of  FIG. 5 . 
       FIG. 6 a    corresponds to a configuration where the B channels of multiplexer pair  506 _ 1  have been selected which effectively forms a direct logical connection between node  1  (which corresponds to the position on the ring of processing core  502 _ 1 ) and node  2  (which corresponds to the position on the ring of processing core  502 _ 2 ). As observed in  FIGS. 5 and 6   a , the selection of the B channels of multiplexer pair  506 _ 1  effectively cuts off processing cores  502 _ 3 ,  502 _ 5 ,  502 _ 7 ,  502 _ 8 ,  502 _ 6  and  502 _ 4  from the ring network. As such, the ring network only couples the I/O unit  505  and processing cores  502 _ 1  and  502 _ 2 . This particular configuration may be chosen, for instance, if the application software program that is to execute on the image processor  500  only includes one or two kernels, in which case, no more than two processing cores are activated (cores  502 _ 1  and cores  502 _ 2 ). The other cores  502 _ 3 ,  502 _ 5 ,  502 _ 7 ,  502 _ 8 ,  502 _ 6  and  502 _ 4  may be placed, e.g., in an inactive low power state to lower the overall power consumption of the image processor. 
       FIG. 6 b    corresponds to a configuration where the A channels of multiplexer pair  506 _ 1  have been selected and the B channels of multiplexer pair  506 _ 2  have been selected. This particular multiplexer configuration expands the ring as compared to the configuration of  FIG. 6 a    so that the ring not only couples cores  502 _ 1  and  502 _ 2  but also couples cores  502 _ 3  and  502 _ 4 . Here, a direct logical connection is formed between node  3  (which corresponds to the position on the ring of processing core  502 _ 3 ) and node  4  (which corresponds to the position on the ring of processing core  502 _ 4 ). As observed in  FIGS. 5 and 6   b , the selection of the A channels of multiplexer pair  506 _ 1  and the B channels of multiplexer pair  506 _ 2  effectively cuts off processing cores  502 _ 5 ,  502 _ 7 ,  502 _ 8  and  502 _ 6  from the ring network. As such, the ring network only couples the I/O unit  505  and processing cores  502 _ 1 ,  502 _ 2 ,  502 _ 3  and  502 _ 4 . 
     This particular configuration may be chosen, for instance, if the application software program that is to execute on the image processor  500  only includes three or four kernels, in which case, no more than four processing cores are activated (cores  502 _ 1 ,  502 _ 2 ,  502 _ 3  and  502 _ 4 ). The other cores  502 _ 5 ,  502 _ 7 ,  502 _ 8  and  502 _ 6  may be placed, e.g., in an inactive low power state to lower the overall power consumption of the image processor. 
       FIG. 6 c    corresponds to a configuration where the A channels of multiplexer pairs  506 _ 1  and  506 _ 2  have been selected and the B channels of multiplexer pair  506 _ 3  have been selected. This particular multiplexer configuration expands the ring as compared to the configuration of  FIG. 6 b    so that the ring not only couples cores  502 _ 1 ,  502 _ 2 ,  502 _ 3  and  502 _ 4  but also couples cores  502 _ 5  and  502 _ 6 . Here, a direct logical connection is formed between node  5  (which corresponds to the position on the ring of processing core  502 _ 5 ) and node  6  (which corresponds to the position on the ring of processing core  502 _ 6 ). As observed in  FIGS. 5 and 6   c , the selection of the A channels of multiplexer pair  506 _ 1  and  506 _ 2  and the B channels of multiplexer pair  506 _ 3  effectively cuts off processing cores  502 _ 7  and  502 _ 8  from the ring network. As such, the ring network couples the I/O unit  505  and processing cores  502 _ 1 ,  502 _ 2 ,  502 _ 3 ,  502 _ 4 ,  502 _ 5  and  502 _ 6 . 
     This particular configuration may be chosen, for instance, if the application software program that is to execute on the image processor  500  only includes five or six kernels, in which case, no more than six processing cores are activated (cores  502 _ 1 ,  502 _ 2 ,  502 _ 3 ,  502 _ 4 ,  502 _ 5  and  502 _ 6 ). The other cores  502 _ 7  and  502 _ 8  may be placed, e.g., in an inactive low power state to lower the overall power consumption of the image processor. 
       FIG. 6 d    corresponds to a configuration where the A channels of multiplexer pairs  506 _ 1 ,  506 _ 2  and  506 _ 3  have been selected. This particular multiplexer configuration expands the ring as compared to the configuration of  FIG. 6 b    so that the ring couples the I/O unit  505  and all of the cores  502 _ 1 ,  502 _ 2 ,  502 _ 3 ,  502 _ 4 ,  502 _ 5 ,  502 _ 6 ,  502 _ 7  and  502 _ 8 . Here, the hardwired connection between node  7  (which corresponds to the position on the ring of processing core  502 _ 7 ) and node  8  (which corresponds to the position on the ring of processing core  502 _ 8 ) forms the right edge of the ring. This particular configuration may be chosen, for instance, if the application software program that is to execute on the image processor  500  includes seven or eight kernels. 
     Another pertinent feature of the network ring design of the processor of  FIG. 5  is the unique arrangement of address value assignments to the different network nodes. Here, referring briefly back to  FIG. 3 , note that the processor  300  of  FIG. 3  numbers the nodes in series around the ring as per usual. However, the network address assignments on the ring network of  FIG. 5  differ from the traditional approach of  FIG. 3  so that the numerical addresses on any active network configuration remains continuous and consecutive irrespective of how many cores are configured to be active on the ring. 
     That is, if the configuration of  FIG. 6 a    is selected, the active numerical addresses on the ring include addresses 0, 1 and 2. By contrast, if the configuration of  FIG. 6 b    is selected, the active numerical addresses on the ring include addresses 0, 1, 2, 3 and 4. Further still, if the configuration of  FIG. 6 c    is selected, the active numerical addresses on the ring include addresses 0, 1, 2, 3, 4, 5 and 6. Finally, if the configuration of  FIG. 6 d    is selected, the active numerical addresses on the ring include addresses 0, 1, 2, 3, 4, 5, 6, 7 and 8. 
     Arranging the network addresses in this manner can help avoid recompilation of application software source code into multiple different lowest level object code (also referred to as binary code) instances even if such lowest level code is reused across different software applications having different configured numbers of active processor cores and correspondingly different underlying ring network configurations. Here, in various environments, a kernel that is the destination of a communication is identified at the source code level of an application software program with a logical address that theoretically can map to, e.g., any core within the actual hardware processor. However, when the source code is compiled into lower level object or binary code, the logical address is converted into the identity of a specific hardware core on the processor (i.e., one of the specific addresses on the ring network). 
     For instance, consider an application software program that uses two kernels K 1  and K 2 , where, the I/O unit sends input data to kernel K 1 , and, kernel K 1  sends its output data to kernel K 2 . After compilation of the source code into lower level object code, assume kernel K 1  is assigned to run specifically on core  502 _ 1  and kernel K 2  is assigned to run specifically on core  502 _ 2 . As such, any object code communication will include a network address of 1 for communications that are sent to kernel K 1  and a network address of 2 for communications that are sent to kernel K 2 . 
     Owing to the unique arrangement of network node address assignments around the ring, this particular instance of lowest level program code is not only operable on the two core processor configuration of  FIG. 6 a   , but also, each of the other processor core configurations of  FIGS. 6 b , 6 c  and 6 d   . As such, the source code for the application software program that includes kernels K 1  and K 2  need not be recompiled into different object code instances should the application software program be targeted to run on different ones of the image processor configurations  6   a ,  6   b ,  6   d ,  6   e . The lack of a need to recompile provides for greater efficiency with respect to application software development and/or construction. 
     That is, program code reuse at the object code level is more easily achieved and/or construction of application software can be accomplished at the object code level using instances of object code as pluggable components into a larger object code application. Consider an example where the aforementioned application software program having kernels K 1  and K 2  performs an operation OP1 that has significant use not only as a stand alone program but also as a front-end operation that is performed before, e.g., a number of other operations having their own unique processing tasks. For simplicity, assume three such other operations exist: 1) OP2 that is implemented with two kernels (e.g., K 3  and K 4 ); 2) OP3 that is implemented with three kernels (e.g., K 3 , K 4  and K 5 ); and, 3) OP4 that is implemented with five kernels (e.g., K 3 , K 4 , K 5 , K 6  and K 7 ). 
     Here, consider an application software development environment in which the OP1 front-end operation is compiled to an object code instance in which kernel K 2  sends its output data to core  502 _ 3  at network node  3  (e.g., rather than the I/O unit  505  at network node  0 ). Additionally, assume that the follow-on operations OP2, OP3 and OP4 are compiled into object code instances such that: 1) the first (input, K 3 ) and second (K 4 ) kernels of OP2, OP3 and OP4 operate on cores  502 _ 3  and  502 _ 4  respectively; 2) the third (K 5 ) kernel of OP3 and OP4 operate on core  502 _ 5 ; and, 3) the fourth (K 6 ) and fifth (K 7 ) kernels of OP4 operate on core  502 _ 6  and  502 _ 7  respectively. 
     In this case, the compiled front-end OP1 instance can be combined “as is” with any of the compiled OP2, OP3 and OP3 object code instances respectively at the object code level to create three separate immediately executable application software programs: 1) a first application software program that corresponds to OP1+OP2; 2) a second application software program that corresponds to OP1+OP3; and, 3) a third application software program that corresponds to OP1+OP4. 
     Here, not only is the object code instance of OP1 separately combinable with each of the OP2, OP3 and OP4 object code instances to create three different object code level applications, but also, note that the first application software program (OP1+OP2) that uses four cores can be configured to operate in the processor configuration of  FIG. 6 b   , the second application software program (OP1+OP3) that uses five cores can be configured to operate in the processor configuration of  FIG. 6 c   , and, the third application software program (OP1+OP4) that uses seven cores can be configured to operate in the processor configuration of  FIG. 6   d.    
     Thus, not only can the object code instance of OP1 be combined with other object code instances and produce larger working object code level applications, but also, the object code instance of OP1 can be so combined even if the combinations that result in different applications require different processor configurations having different numbers of active hardware cores and correspondingly different internal ring network configurations. That is, program code construction can be accomplished at the object code level that is indifferent to the configuration/number of active cores in the target hardware processor even though the internal network within the processor is different across the different processor configurations. 
     Furthermore, with use of abstract kernel identifiers at the object code level, any object code program can readily plug into larger object code level constructions and be configured to execute on different processor cores. For example, assume the object code instance of OP3 discussed above as compiled: 1) identifies its first kernel (K 3  from the discussion above) with an input variable=BASE; 2) identifies its second kernel (K 4  from the discussion above) with an identifier=BASE+1; and, 3) identifies is third kernel (K 5  from the discussion above) with an identifier=BASE+2. In this case, the configuration of OP3&#39;s object code for utilization with the second (OP1+OP3) application discussed above is straightforward by setting BASE=3. 
     Moreover, reuse of an identical instance of the OP3 object code for stand alone operation can also be readily accomplished simply by setting BASE=1. The later will cause OP3&#39;s first kernel to execute on core  502 _ 1  and its second core to operate on core  502 _ 2  with correct kernel to kernel communications on the network ring. Thus, with a simple change of input variable/configuration information (BASE), identical instances of OP3 at the object code level can be made to readily operate in the processor configuration of  FIG. 6 c    (for the second application (OP1+OP3) discussed just above), or operate as a stand alone application in the processor configuration of  FIG. 6   a.    
     As such, identifying the different kernels within an object level program by their network address offsets with respect to one another, identical instances of an object level program can be easily mapped to different processor configurations because the unique addressing pattern on the processor&#39;s network ring essentially preserves the meaning of these offsets even though the numbers of nodes on the ring change with each different processor configuration. As such, in many situations, once an object code instance of a program is created, identical copies of it can be reused for many different applications and corresponding configurations as a “plug-in” rather than compiling a new instance of object code from a same source code level for, e.g., each new use of the function of the program or different underlying processor configuration. 
     The ability to plug-in an object code instance into a larger object code construction is also enhanced if the address from which the input stream originates and/or the address where the output stream is to be sent is also specified as respective input variables at the object code level. For example, again using OP3 as an example, when OP3 is utilized for the second (OP1+OP3) application discussed above and BASE=3, an additional input variable IN that identifies where the input data for OP3 is coming from may be set as IN=2 (K 2  of OP1 executing on core  502 _ 2  sends OP3 its input data for the OP1+OP3 application). The destination that identifies where OP3 is to send its output information may be specified with another variable OUT that is set as OUT=0 (OP3 sends its output data to the I/O unit  505  when used in the OP1+OP3 application). As discussed above, with these settings, the object code instance of OP3 can operate within the OP1+OP2 application with the processor being set in the configuration of  FIG. 6   c.    
     In order to reuse a copy of the same instance of the OP3 object code for stand alone operation, the input configuration information need only be set to IN=OUT=0 and BASE=1). With this configuration, OP3 will receive its input data from the I/O unit  505  and will send its output data to the I/O unit  505 . Also with this configuration, the OP3 instance can operate in the processor configuration of  FIG. 6 a   . As such, identical instance of the OP3 code are essentially indifferent to the underlying processor configuration which includes different internal network ring configurations. 
     Thus, the overall application software development environment can include the development of smaller granularized application software programs at the source code level that are written to perform basic, often used/reused processing functions. The smaller granularized source code applications are compiled into respective object code instances. The object code instances are then copied as needed and combined with other copies of object code instances to form larger, more comprehensive executable object code level applications. 
     An even further efficiency can be realized if different hardware platforms exist having different numbers of cores. Here, the discussions above pertaining to  FIGS. 6 a  through 6 d    were directed to a single hardware platform having eight cores where the eight core platform could be configured with two, four, six or eight active cores. Again, it was shown above that, e.g., a two kernel object code level program (e.g., OP1) could operate on any of these configurations without having two recompile new object code instances for the OP1 program. 
     This versatility can extend even further to, e.g., a product line composed of: 1) a first hardware platform composed of only two cores that supports a single configuration of two active cores; 2) a second hardware platform composed of four cores that supports a first configuration of two active cores and a second configuration of four active cores; 3) a third hardware platform composed of six cores that supports a first configuration that supports two cores, a second configuration that supports four cores and a third configuration that supports six cores; and, 4) a fourth hardware platform composed of eight cores that supports the four different configurations described above with respect to  FIGS. 6 a    through  6   d.    
     It was described at length above that an object code level program OP1 that uses two kernels would be operable on each of the four configurations of the hardware platform of 4) above. However, if the hardware platforms of 1), 2) and 3) above are designed to enumerate the network nodes as described herein, the object code level program OP1 that is operable on all four configurations of hardware platform 4) above will also be operable on any of: i) the three different configurations of the hardware platform of 3) above; ii) the two different configurations of the hardware platform of 2) above; and, iii) the hardware platform of 1) above. As such, the code re-use capability not only extends to different configurations of a same hardware platform but also the different configurations of different hardware platforms. The code can be stand alone or combined with other object code level programs as described above. 
       FIG. 7  shows a method described above. As observed in  FIG. 7 , the method includes configuring  701  a first instance of object code to execute on a processor, the processor having multiple cores and an internal network, the internal network configured in a first configuration that enables a first number of the cores to be communicatively coupled. The method also includes configuring  702  a second instance of the object code to execute on a second instance of the processor, a respective internal network of the second instance of the processor configured in a second configuration that enables a different number of cores to be communicatively coupled, wherein, same positioned cores on the processor and the second instance of the processor have same network addresses for the first and second configurations. 
     It is pertinent to recognize that ideas described above are not limited to the specific processor of  FIG. 5 . Here, other processors having, e.g., different numbers of processing cores or even different types of internal network topologies may make use of the teachings herein. That is, other network topologies (e.g., a switched connection network) may be designed to keep the physical addresses of its source/destination nodes constant across different internal network configurations and/or keep the physical addresses continuous and consecutive across the different internal network configurations. 
     3.0 Image Processor Implementation Embodiments 
       FIGS. 8 a - e    through  FIG. 12  provide additional details concerning operation and design of various embodiments for the image processor and associated stencil processor described at length above. Recalling from the discussion of  FIG. 2  that a line buffer unit feeds line groups to a stencil processor&#39;s associated sheet generator,  FIGS. 8 a  through 8 e    illustrate at a high level embodiments of both the parsing activity of a line buffer unit  201 , the finer grained parsing activity of a sheet generator unit  203  as well as the stencil processing activity of the stencil processor  702  that is coupled to the sheet generator unit  203 . 
       FIG. 8 a    depicts an embodiment of an input frame of image data  801 .  FIG. 8 a    also depicts an outline of three overlapping stencils  802  (each having a dimension of 3 pixels×3 pixels) that a stencil processor is designed to operate over. The output pixel that each stencil respectively generates output image data for is highlighted in solid black. For simplicity, the three overlapping stencils  802  are depicted as overlapping only in the vertical direction. It is pertinent to recognize that in actuality a stencil processor may be designed to have overlapping stencils in both the vertical and horizontal directions. 
     Because of the vertical overlapping stencils  802  within the stencil processor, as observed in  FIG. 8 a   , there exists a wide band of image data within the frame that a single stencil processor can operate over. As will be discussed in more detail below, in an embodiment, the stencil processors process data within their overlapping stencils in a left to right fashion across the image data (and then repeat for the next set of lines, in top to bottom order). Thus, as the stencil processors continue forward with their operation, the number of solid black output pixel blocks will grow right-wise horizontally. As discussed above, a line buffer unit  201  is responsible for parsing a line group of input image data from an incoming frame that is sufficient for the stencil processors to operate over for an extended number of upcoming cycles. An exemplary depiction of a line group is illustrated as a shaded region  803 . In an embodiment, the line buffer unit  201  can comprehend different dynamics for sending/receiving a line group to/from a sheet generator. For example, according to one mode, referred to as “full group”, the complete full width lines of image data are passed between a line buffer unit and a sheet generator. According to a second mode, referred to as “virtually tall”, a line group is passed initially with a subset of full width rows. The remaining rows are then passed sequentially in smaller (less than full width) pieces. 
     With the line group  803  of the input image data having been defined by the line buffer unit and passed to the sheet generator unit, the sheet generator unit further parses the line group into finer sheets that are more precisely fitted to the hardware limitations of the stencil processor. More specifically, as will be described in more detail further below, in an embodiment, each stencil processor consists of a two dimensional shift register array. The two dimensional shift register array essentially shifts image data “beneath” an array of execution lanes where the pattern of the shifting causes each execution lane to operate on data within its own respective stencil (that is, each execution lane processes on its own stencil of information to generate an output for that stencil). In an embodiment, sheets are surface areas of input image data that “fill” or are otherwise loaded into the two dimensional shift register array. 
     As will be described in more detail below, in various embodiments, there are actually multiple layers of two dimensional register data that can be shifted on any cycle. For convenience, much of the present description will simply use the term “two-dimensional shift register” and the like to refer to structures that have one or more such layers of two-dimensional register data that can be shifted. 
     Thus, as observed in  FIG. 8 b   , the sheet generator parses an initial sheet  804  from the line group  803  and provides it to the stencil processor (here, the sheet of data corresponds to the shaded region that is generally identified by reference number  804 ). As observed in  FIGS. 8 c  and 8 d   , the stencil processor operates on the sheet of input image data by effectively moving the overlapping stencils  802  in a left to right fashion over the sheet. As of  FIG. 8 d   , the number of pixels for which an output value could be calculated from the data within the sheet is exhausted (no other pixel positions can have an output value determined from the information within the sheet). For simplicity the border regions of the image have been ignored. 
     As observed in  FIG. 8 e    the sheet generator then provides a next sheet  805  for the stencil processor to continue operations on. Note that the initial positions of the stencils as they begin operation on the next sheet is the next progression to the right from the point of exhaustion on the first sheet (as depicted previously in  FIG. 8 d   ). With the new sheet  805 , the stencils will simply continue moving to the right as the stencil processor operates on the new sheet in the same manner as with the processing of the first sheet. 
     Note that there is some overlap between the data of the first sheet  804  and the data of the second sheet  805  owing to the border regions of stencils that surround an output pixel location. The overlap could be handled simply by the sheet generator re-transmitting the overlapping data twice. In alternate implementations, to feed a next sheet to the stencil processor, the sheet generator may proceed to only send new data to the stencil processor and the stencil processor reuses the overlapping data from the previous sheet. 
       FIG. 9  shows an embodiment of a stencil processor architecture  900 . As observed in  FIG. 9 , the stencil processor includes a data computation unit  901 , a scalar processor  902  and associated memory  903  and an I/O unit  904 . The data computation unit  901  includes an array of execution lanes  905 , a two-dimensional shift array structure  906  and separate random access memories  907  associated with specific rows or columns of the array. 
     The I/O unit  904  is responsible for loading “input” sheets of data received from the sheet generator into the data computation unit  901  and storing “output” sheets of data from the stencil processor into the sheet generator. In an embodiment the loading of sheet data into the data computation unit  901  entails parsing a received sheet into rows/columns of image data and loading the rows/columns of image data into the two dimensional shift register structure  906  or respective random access memories  907  of the rows/columns of the execution lane array (described in more detail below). If the sheet is initially loaded into memories  907 , the individual execution lanes within the execution lane array  905  may then load sheet data into the two-dimensional shift register structure  906  from the random access memories  907  when appropriate (e.g., as a load instruction just prior to operation on the sheet&#39;s data). Upon completion of the loading of a sheet of data into the register structure  906  (whether directly from a sheet generator or from memories  907 ), the execution lanes of the execution lane array  905  operate on the data and eventually “write back” finished data as a sheet directly back to the sheet generator, or, into the random access memories  907 . If the later the I/O unit  904  fetches the data from the random access memories  907  to form an output sheet which is then forwarded to the sheet generator. 
     The scalar processor  902  includes a program controller  909  that reads the instructions of the stencil processor&#39;s program code from scalar memory  903  and issues the instructions to the execution lanes in the execution lane array  905 . In an embodiment, a single same instruction is broadcast to all execution lanes within the array  905  to effect a SIMD-like behavior from the data computation unit  901 . In an embodiment, the instruction format of the instructions read from scalar memory  903  and issued to the execution lanes of the execution lane array  905  includes a very-long-instruction-word (VLIW) type format that includes more than one opcode per instruction. In a further embodiment, the VLIW format includes both an ALU opcode that directs a mathematical function performed by each execution lane&#39;s ALU (which, as described below, in an embodiment may specify more than one traditional ALU operation) and a memory opcode (that directs a memory operation for a specific execution lane or set of execution lanes). 
     The term “execution lane” refers to a set of one or more execution units capable of executing an instruction (e.g., logic circuitry that can execute an instruction). An execution lane can, in various embodiments, include more processor-like functionality beyond just execution units, however. For example, besides one or more execution units, an execution lane may also include logic circuitry that decodes a received instruction, or, in the case of more MIMD-like designs, logic circuitry that fetches and decodes an instruction. With respect to MIMD-like approaches, although a centralized program control approach has largely been described herein, a more distributed approach may be implemented in various alternative embodiments (e.g., including program code and a program controller within each execution lane of the array  905 ). 
     The combination of an execution lane array  905 , program controller  909  and two dimensional shift register structure  906  provides a widely adaptable/configurable hardware platform for a broad range of programmable functions. For example, application software developers are able to program kernels having a wide range of different functional capability as well as dimension (e.g., stencil size) given that the individual execution lanes are able to perform a wide variety of functions and are able to readily access input image data proximate to any output array location. 
     Apart from acting as a data store for image data being operated on by the execution lane array  905 , the random access memories  907  may also keep one or more look-up tables. In various embodiments one or more scalar look-up tables may also be instantiated within the scalar memory  903 . 
     A scalar look-up involves passing the same data value from the same look-up table from the same index to each of the execution lanes within the execution lane array  905 . In various embodiments, the VLIW instruction format described above is expanded to also include a scalar opcode that directs a look-up operation performed by the scalar processor into a scalar look-up table. The index that is specified for use with the opcode may be an immediate operand or fetched from some other data storage location. Regardless, in an embodiment, a look-up from a scalar look-up table within scalar memory essentially involves broadcasting the same data value to all execution lanes within the execution lane array  905  during the same clock cycle. Additional details concerning use and operation of look-up tables is provided further below. 
       FIG. 9 b    summarizes the VLIW instruction word embodiments(s) discussed above. As observed in  FIG. 9 b   , the VLIW instruction word format includes fields for three separate instructions: 1) a scalar instruction  951  that is executed by the scalar processor; 2) an ALU instruction  952  that is broadcasted and executed in SIMD fashion by the respective ALUs within the execution lane array; and, 3) a memory instruction  953  that is broadcasted and executed in a partial SIMD fashion (e.g., if execution lanes along a same row in the execution lane array share a same random access memory, then one execution lane from each of the different rows actually execute the instruction (the format of the memory instruction  953  may include an operand that identifies which execution lane from each row executes the instruction). 
     A field  954  for one or more immediate operands is also included. Which of the instructions  951 ,  952 ,  953  use which immediate operand information may be identified in the instruction format. Each of instructions  951 ,  952 ,  953  also include their own respective input operand and resultant information (e.g., local registers for ALU operations and a local register and a memory address for memory access instructions). In an embodiment, the scalar instruction  951  is executed by the scalar processor before the execution lanes within the execution lane array execute either of the other to instructions  952 ,  953 . That is, the execution of the VLIW word includes a first cycle upon which the scalar instruction  951  is executed followed by a second cycle upon with the other instructions  952 ,  953  may be executed (note that in various embodiments instructions  952  and  953  may be executed in parallel). 
     In an embodiment, the scalar instructions executed by the scalar processor include commands issued to the sheet generator to load/store sheets from/into the memories or 2D shift register of the data computation unit. Here, the sheet generator&#39;s operation can be dependent on the operation of the line buffer unit or other variables that prevent pre-runtime comprehension of the number of cycles it will take the sheet generator to complete any command issued by the scalar processor. As such, in an embodiment, any VLIW word whose scalar instruction  951  corresponds to or otherwise causes a command to be issued to the sheet generator also includes no-operation (NOOP) instructions in the other two instruction field  952 ,  953 . The program code then enters a loop of NOOP instructions for instruction fields  952 ,  953  until the sheet generator completes its load/store to/from the data computation unit. Here, upon issuing a command to the sheet generator, the scalar processor may set a bit of an interlock register that the sheet generator resets upon completion of the command. During the NOOP loop the scalar processor monitors the bit of the interlock bit. When the scalar processor detects that the sheet generator has completed its command normal execution begins again. 
       FIG. 10  shows an embodiment of a data computation component  1001 . As observed in  FIG. 10 , the data computation component  1001  includes an array of execution lanes  1005  that are logically positioned “above” a two-dimensional shift register array structure  1006 . As discussed above, in various embodiments, a sheet of image data provided by a sheet generator is loaded into the two-dimensional shift register  1006 . The execution lanes then operate on the sheet data from the register structure  1006 . 
     The execution lane array  1005  and shift register structure  1006  are fixed in position relative to one another. However, the data within the shift register array  1006  shifts in a strategic and coordinated fashion to cause each execution lane in the execution lane array to process a different stencil within the data. As such, each execution lane determines the output image value for a different pixel in the output sheet being generated. From the architecture of  FIG. 10  it should be clear that overlapping stencils are not only arranged vertically but also horizontally as the execution lane array  1005  includes vertically adjacent execution lanes as well as horizontally adjacent execution lanes. 
     Some notable architectural features of the data computation unit  1001  include the shift register structure  1006  having wider dimensions than the execution lane array  1005 . That is, there is a “halo” of registers  1009  outside the execution lane array  1005 . Although the halo  1009  is shown to exist on two sides of the execution lane array, depending on implementation, the halo may exist on less (one) or more (three or four) sides of the execution lane array  1005 . The halo  1005  serves to provide “spill-over” space for data that spills outside the bounds of the execution lane array  1005  as the data is shifting “beneath” the execution lanes  1005 . As a simple case, a 5×5 stencil centered on the right edge of the execution lane array  1005  will need four halo register locations further to the right when the stencil&#39;s leftmost pixels are processed. For ease of drawing,  FIG. 10  shows the registers of the right side of the halo as only having horizontal shift connections and registers of the bottom side of the halo as only having vertical shift connections when, in a nominal embodiment, registers on either side (right, bottom) would have both horizontal and vertical connections. In various embodiments, the halo region does not include corresponding execution lane logic to execute image processing instructions (e.g., no ALU is present). However, individual memory access units (M) are present in each of the halo region locations so that the individual halo register locations can individually load data from memory and store data to memory. 
     Additional spill-over room is provided by random access memories  1007  that are coupled to each row and/or each column in the array, or portions thereof (E.g., a random access memory may be assigned to a “region” of the execution lane array that spans 4 execution lanes row wise and 2 execution lanes column wise. For simplicity the remainder of the application will refer mainly to row and/or column based allocation schemes). Here, if a execution lane&#39;s kernel operations require it to process pixel values outside of the two-dimensional shift register array  1006  (which some image processing routines may require) the plane of image data is able to further spill-over, e.g., from the halo region  1009  into random access memory  1007 . For example, consider a 6×6 stencil where the hardware includes a halo region of only four storage elements to the right of a execution lane on the right edge of the execution lane array. In this case, the data would need to be shifted further to the right off the right edge of the halo  1009  to fully process the stencil. Data that is shifted outside the halo region  1009  would then spill-over to random access memory  1007 . Other applications of the random access memories  1007  and the stencil processor of  FIG. 9  are provided further below. 
       FIGS. 11 a  through 11 k    demonstrate a working example of the manner in which image data is shifted within the two dimensional shift register array “beneath” the execution lane array as alluded to above. As observed in  FIG. 11 a   , the data contents of the two dimensional shift array are depicted in a first array  1107  and the execution lane array is depicted by a frame  1105 . Also, two neighboring execution lanes  1110  within the execution lane array are simplistically depicted. In this simplistic depiction  1110 , each execution lane includes a register R 1  that can accept data from the shift register, accept data from an ALU output (e.g., to behave as an accumulator across cycles), or write output data into an output destination. 
     Each execution lane also has available, in a local register R 2 , the contents “beneath” it in the two dimensional shift array. Thus, R 1  is a physical register of the execution lane while R 2  is a physical register of the two dimensional shift register array. The execution lane includes an ALU that can operate on operands provided by R 1  and/or R 2 . As will be described in more detail further below, in an embodiment the shift register is actually implemented with multiple (a “depth” of) storage/register elements per array location but the shifting activity is limited to one plane of storage elements (e.g., only one plane of storage elements can shift per cycle).  FIGS. 11 a  through 11 k    depict one of these deeper register locations as being used to store the resultant X from the respective execution lanes. For illustrative ease the deeper resultant register is drawn alongside rather than beneath its counterpart register R 2 . 
       FIGS. 11 a  through 11 k    focus on the calculation of two stencils whose central position is aligned with the pair of execution lane positions  1111  depicted within the execution lane array. For ease of illustration, the pair of execution lanes  1110  are drawn as horizontal neighbors when in fact, according to the following example, they are vertical neighbors. 
     As observed initially in  FIG. 11 a   , the execution lanes are centered on their central stencil locations.  FIG. 11 b    shows the object code executed by both execution lanes. As observed in  FIG. 11 b    the program code of both execution lanes causes the data within the shift register array to shift down one position and shift right one position. This aligns both execution lanes to the upper left hand corner of their respective stencils. The program code then causes the data that is located (in R 2 ) in their respective locations to be loaded into R 1 . 
     As observed in  FIG. 11 c    the program code next causes the pair of execution lanes to shift the data within the shift register array one unit to the left which causes the value to the right of each execution lane&#39;s respective position to be shifted into each execution lane&#39; position. The value in R 1  (previous value) is then added with the new value that has shifted into the execution lane&#39;s position (in R 2 ). The resultant is written into R 1 . As observed in  FIG. 11 d    the same process as described above for  FIG. 11 c    is repeated which causes the resultant R 1  to now include the value A+B+C in the upper execution lane and F+G+H in the lower execution lane. At this point both execution lanes have processed the upper row of their respective stencils. Note the spill-over into a halo region on the left side of the execution lane array (if one exists on the left hand side) or into random access memory if a halo region does not exist on the left hand side of the execution lane array. 
     As observed in  FIG. 11 e   , the program code next causes the data within the shift register array to shift one unit up which causes both execution lanes to be aligned with the right edge of the middle row of their respective stencils. Register R 1  of both execution lanes currently includes the summation of the stencil&#39;s top row and the middle row&#39;s rightmost value.  FIGS. 11 f  and 11 g    demonstrate continued progress moving leftwise across the middle row of both execution lane&#39;s stencils. The accumulative addition continues such that at the end of processing of  FIG. 11 g    both execution lanes include the summation of the values of the top row and the middle row of their respective stencils. 
       FIG. 11 h    shows another shift to align each execution lane with its corresponding stencil&#39;s lowest row.  FIGS. 11 i  and 11 j    show continued shifting to complete processing over the course of both execution lanes&#39; stencils.  FIG. 11 k    shows additional shifting to align each execution lane with its correct position in the data array and write the resultant thereto. 
     In the example of  FIGS. 11 a -11 k    note that the object code for the shift operations may include an instruction format that identifies the direction and magnitude of the shift expressed in (X, Y) coordinates. For example, the object code for a shift up by one location may be expressed in object code as SHIFT 0, +1. As another example, a shift to the right by one location may expressed in object code as SHIFT+1, 0. In various embodiments shifts of larger magnitude may also be specified in object code (e.g., SHIFT 0, +2). Here, if the 2D shift register hardware only supports shifts by one location per cycle, the instruction may be interpreted by the machine to require multiple cycle execution, or, the 2D shift register hardware may be designed to support shifts by more than one location per cycle. Embodiments of the later are described in more detail further below. 
       FIG. 12  shows another, more detailed depiction of the unit cell for an execution lane and corresponding shift register structure (registers in the halo region do not include a corresponding execution lane but do include a memory unit in various embodiments). The execution lane and the register space associated with each location in the execution lane array is, in an embodiment, implemented by instantiating the circuitry observed in  FIG. 12  at each node of the execution lane array. As observed in  FIG. 12 , the unit cell includes a execution lane  1201  coupled to a register file  1202  consisting of four registers R 2  through R 5 . During any cycle, the execution lane  1201  may read from or write to any of registers R 1  through R 5 . For instructions requiring two input operands the execution lane may retrieve both of operands from any of R 1  through R 5 . 
     In an embodiment, the two dimensional shift register structure is implemented by permitting, during a single cycle, the contents of any of (only) one of registers R 2  through R 4  to be shifted “out” to one of its neighbor&#39;s register files through output multiplexer  1203 , and, having the contents of any of (only) one of registers R 2  through R 4  replaced with content that is shifted “in” from a corresponding one if its neighbors through input multiplexers  1204  such that shifts between neighbors are in a same direction (e.g., all execution lanes shift left, all execution lanes shift right, etc.). Although it may be common for a same register to have its contents shifted out and replaced with content that is shifted in on a same cycle, the multiplexer arrangement  1203 ,  1204  permits for different shift source and shift target registers within a same register file during a same cycle. 
     As depicted in  FIG. 12  note that during a shift sequence a execution lane will shift content out from its register file  1202  to each of its left, right, top and bottom neighbors. In conjunction with the same shift sequence, the execution lane will also shift content into its register file from a particular one of its left, right, top and bottom neighbors. Again, the shift out target and shift in source should be consistent with a same shift direction for all execution lanes (e.g., if the shift out is to the right neighbor, the shift in should be from the left neighbor). 
     Although in one embodiment the content of only one register is permitted to be shifted per execution lane per cycle, other embodiments may permit the content of more than one register to be shifted in/out. For example, the content of two registers may be shifted out/in during a same cycle if a second instance of the multiplexer circuitry  1203 ,  1204  observed in  FIG. 12  is incorporated into the design of  FIG. 12 . Of course, in embodiments where the content of only one register is permitted to be shifted per cycle, shifts from multiple registers may take place between mathematical operations by consuming more clock cycles for shifts between mathematical operations (e.g., the contents of two registers may be shifted between math ops by consuming two shift ops between the math ops). 
     If less than all the content of a execution lane&#39;s register files are shifted out during a shift sequence note that the content of the non shifted out registers of each execution lane remain in place (do not shift). As such, any non shifted content that is not replaced with shifted in content persists local to the execution lane across the shifting cycle. The memory unit (“M”) observed in each execution lane is used to load/store data from/to the random access memory space that is associated with the execution lane&#39;s row and/or column within the execution lane array. Here, the M unit acts as a standard M unit in that it is often used to load/store data that cannot be loaded/stored from/to the execution lane&#39;s own register space. In various embodiments, the primary operation of the M unit is to write data from a local register into memory, and, read data from memory and write it into a local register. 
     With respect to the ISA opcodes supported by the ALU unit of the hardware execution lane  1201 , in various embodiments, the mathematical opcodes supported by the hardware ALU include (e.g., ADD, SUB, MOV, MUL, MAD, ABS, DIV, SHL, SHR, MIN/MAX, SEL, AND, OR, XOR, NOT). As described just above, memory access instructions can be executed by the execution lane  1201  to fetch/store data from/to their associated random access memory. Additionally the hardware execution lane  1201  supports shift op instructions (right, left, up, down) to shift data within the two dimensional shift register structure. As described above, program control instructions are largely executed by the scalar processor of the stencil processor. 
     4.0 Implementation Embodiments 
     It is pertinent to point out that the various image processor architecture features described above are not necessarily limited to image processing in the traditional sense and therefore may be applied to other applications that may (or may not) cause the image processor to be re-characterized. For example, if any of the various image processor architecture features described above were to be used in the creation and/or generation and/or rendering of animation as opposed to the processing of actual camera images, the image processor may be characterized as a graphics processing unit. Additionally, the image processor architectural features described above may be applied to other technical applications such as video processing, vision processing, image recognition and/or machine learning. Applied in this manner, the image processor may be integrated with (e.g., as a co-processor to) a more general purpose processor (e.g., that is or is part of a CPU of computing system), or, may be a stand alone processor within a computing system. 
     The hardware design embodiments discussed above may be embodied within a semiconductor chip and/or as a description of a circuit design for eventual targeting toward a semiconductor manufacturing process. In the case of the later, such circuit descriptions may take of the form of a (e.g., VHDL or Verilog) register transfer level (RTL) circuit description, a gate level circuit description, a transistor level circuit description or mask description or various combinations thereof. Circuit descriptions are typically embodied on a computer readable storage medium (such as a CD-ROM or other type of storage technology). 
     From the preceding sections is pertinent to recognize that an image processor as described above may be embodied in hardware on a computer system (e.g., as part of a handheld device&#39;s System on Chip (SOC) that processes data from the handheld device&#39;s camera). In cases where the image processor is embodied as a hardware circuit, note that the image data that is processed by the image processor may be received directly from a camera. Here, the image processor may be part of a discrete camera, or, part of a computing system having an integrated camera. In the case of the later the image data may be received directly from the camera or from the computing system&#39;s system memory (e.g., the camera sends its image data to system memory rather than the image processor). Note also that many of the features described in the preceding sections may be applicable to a graphics processor unit (which renders animation). 
       FIG. 13  provides an exemplary depiction of a computing system. Many of the components of the computing system described below are applicable to a computing system having an integrated camera and associated image processor (e.g., a handheld device such as a smartphone or tablet computer). Those of ordinary skill will be able to easily delineate between the two. Additionally, the computing system of  FIG. 13  also includes many features of a high performance computing system, such as a workstation or supercomputer. 
     As observed in  FIG. 13 , the basic computing system may include a central processing unit  1301  (which may include, e.g., a plurality of general purpose processing cores  1315 _ 1  through  1315 _N and a main memory controller  1317  disposed on a multi-core processor or applications processor), system memory  1302 , a display  1303  (e.g., touchscreen, flat-panel), a local wired point-to-point link (e.g., USB) interface  1304 , various network I/O functions  1305  (such as an Ethernet interface and/or cellular modem subsystem), a wireless local area network (e.g., WiFi) interface  1306 , a wireless point-to-point link (e.g., Bluetooth) interface  1307  and a Global Positioning System interface  1308 , various sensors  1309 _ 1  through  1309 _N, one or more cameras  1310 , a battery  1311 , a power management control unit  1312 , a speaker and microphone  1313  and an audio coder/decoder  1314 . 
     An applications processor or multi-core processor  1350  may include one or more general purpose processing cores  1315  within its CPU  1201 , one or more graphical processing units  1316 , a memory management function  1317  (e.g., a memory controller), an I/O control function  1318  and an image processing unit  1319 . The general purpose processing cores  1315  typically execute the operating system and application software of the computing system. The graphics processing units  1316  typically execute graphics intensive functions to, e.g., generate graphics information that is presented on the display  1303 . The memory control function  1317  interfaces with the system memory  1302  to write/read data to/from system memory  1302 . The power management control unit  1312  generally controls the power consumption of the system  1300 . 
     The image processing unit  1319  may be implemented according to any of the image processing unit embodiments described at length above in the preceding sections. Alternatively or in combination, the IPU  1319  may be coupled to either or both of the GPU  1316  and CPU  1301  as a co-processor thereof. Additionally, in various embodiments, the GPU  1316  may be implemented with any of the image processor features described at length above. The image processing unit  1319  may be configured with application software as described at length above. Additionally, a computing system such as the computing system of  FIG. 13  may execute program code to implement the application software development described above. 
     Each of the touchscreen display  1303 , the communication interfaces  1304 - 1307 , the GPS interface  1308 , the sensors  1309 , the camera  1310 , and the speaker/microphone codec  1313 ,  1314  all can be viewed as various forms of I/O (input and/or output) relative to the overall computing system including, where appropriate, an integrated peripheral device as well (e.g., the one or more cameras  1310 ). Depending on implementation, various ones of these I/O components may be integrated on the applications processor/multi-core processor  1350  or may be located off the die or outside the package of the applications processor/multi-core processor  1350 . 
     In an embodiment one or more cameras  1310  includes a depth camera capable of measuring depth between the camera and an object in its field of view. Application software, operating system software, device driver software and/or firmware executing on a general purpose CPU core (or other functional block having an instruction execution pipeline to execute program code) of an applications processor or other processor may perform any of the functions described above. 
     Embodiments of the invention may include various processes as set forth above. The processes may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain processes. Alternatively, these processes may be performed by specific hardware components that contain hardwired and/or programmable logic for performing the processes, or by any combination of programmed computer components and custom hardware components. 
     Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, FLASH memory, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.