Abstract:
A clock-less asynchronous processing circuit or system having a plurality of pipelined processing stages utilizes self-clocked generators to tune the delay needed in each of the processing stages to complete the processing cycle. Because different processing stages may require different amounts of time to complete processing or may require different delays depending on the processing required in a particular stage, the self-clocked generators may be tuned to each stage&#39;s necessary delay(s) or may be programmably configured.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 USC 119(e) to U.S. Provisional Applications Ser. No. 61/874,794, 61/874,810, 61/874,856, 61/874,914, 61/874,880, 61/874,889, and 61/874,866, all filed on Sep. 6, 2013, and all of which are incorporated herein by reference. 
         [0002]    This application is related to: 
         [0003]    U.S. patent application Ser. No. ______ entitled “METHOD AND APPARATUS FOR ASYNCHRONOUS PROCESSOR WITH FAST AND SLOW MODE” and filed on the same date herewith, and identified by attorney docket number HUAW07-06583, and which is incorporated herein by reference; 
         [0004]    U.S. patent application Ser. No. ______ entitled “METHOD AND APPARATUS FOR ASYNCHRONOUS PROCESSOR WITH AUXILIARY ASYNCHRONOUS VECTOR PROCESSOR” and filed on the same date herewith, and identified by attorney docket number HUAW07-06502, and which is incorporated herein by reference; 
         [0005]    U.S. patent application Ser. No. ______ entitled “METHOD AND APPARATUS FOR ASYNCHRONOUS PROCESSOR WITH A TOKEN RING BASED PARALLEL PROCESSOR SCHEDULER” and filed on the same date herewith, and identified by attorney docket number HUAW07-06376, and which is incorporated herein by reference; 
         [0006]    U.S. patent application Ser. No. ______ entitled “METHOD AND APPARATUS FOR ASYNCHRONOUS PROCESSOR PIPELINE AND BYPASS PASSING” and filed on the same date herewith, and identified by attorney docket number HUAW07-06364, and which is incorporated herein by reference; and 
         [0007]    U.S. patent application Ser. No. ______ entitled “METHOD AND APPARATUS FOR ASYNCHRONOUS PROCESSOR BASED ON CLOCK DELAY ADJUSTMENT” and filed on the same date herewith, and identified by attorney docket number HUAW07-06351, and which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0008]    The present disclosure relates generally to asynchronous circuit technology, and more particularly, to a self-clocked circuit generating a clocking signal using a programmable time period. 
       BACKGROUND 
       [0009]    High performance synchronous digital processing systems utilize pipelining to increase parallel performance and throughput. In synchronous systems, pipelining results in many partitioned or subdivided smaller blocks or stages and a system clock is applied to registers between the blocks/stages. The system clock initiates movement of the processing and data from one stage to the next, and the processing in each stage must be completed during one fixed clock cycle. When certain stages take less time than a clock cycle to complete processing, the next processing stages must wait—increasing processing delays (which are additive). 
         [0010]    In contrast, asynchronous systems (i.e., clockless) do not utilize a system clock and each processing stage is intended, in general terms, to begin its processing upon completion of processing in the prior stage. Several benefits or features are present with asynchronous processing systems. Each processing stage can have a different processing delay, the input data can be processed upon arrival, and consume power only on demand. 
         [0011]      FIG. 1  illustrates a prior art Sutherland asynchronous micro-pipeline architecture  100 . The Sutherland asynchronous micro-pipeline architecture is one form of asynchronous micro-pipeline architecture that uses a handshaking protocol built by Muller-C elements to control the micro-pipeline building blocks. The architecture  100  includes a plurality of computing logic  102  linked in sequence via flip-flops or latches  104  (e.g., registers). Control signals are passed between the computing blocks via Muller C-elements  106  and delayed via delay logic  108 . Further information describing this architecture  100  is published by Ivan Sutherland in Communications of the ACM Volume 32 Issue 6, June 1989 pages 720-738, ACM New York, N.Y., USA, which is incorporated herein by reference. 
         [0012]    Now turning to  FIG. 2 , there is illustrated a typical section or processing stage of a synchronous system  200 . The system  200  includes flip-flops or registers  202 ,  204  for clocking an output signal (data)  206  from a logic block  210 . On the right side of  FIG. 2  there is shown an illustration of the concept of meta-stability. Set-up times and hold times must be considered to avoid meta-stability. In other words, the data must be valid and held during the set-up time and the hold time, otherwise a set-up violation  212  or a hold violation  214  may occur. If either of these violations occurs, the synchronous system may malfunction. The concept of meta-stability also applies to asynchronous systems. Therefore, it is important to design asynchronous systems to avoid meta-stability. In addition, like synchronous systems, asynchronous systems also need to address various potential data/instruction hazards, and should include a bypassing mechanism and pipeline interlock mechanism to detect and resolve hazards. 
         [0013]    Accordingly, there are needed asynchronous processing systems, asynchronous processors, and methods of asynchronous processing that are stable, and detect and resolve potential hazards (i.e, remove meta-stability). 
       SUMMARY 
       [0014]    According to one embodiment, there is provided a clock-less asynchronous processor including a processing pipeline having a plurality of successive processing stages. Each processing stage includes asynchronous logic circuitry configured to process input data and output processed data, and a data storage element coupled to the asynchronous logic circuitry and configured to receive and store the processed output data in response to a current stage active complete signal. A self-clocked generator configured to receive a previous stage active complete signal is also included in each stage to generate the current active complete signal in response thereto, and output the current active complete signal to the data storage element and to a next processing stage. 
         [0015]    In another embodiment, there is provided a method of operating a clock-less asynchronous processor having a processing pipeline having a plurality of successive processing stages, where each processing stage includes asynchronous logic circuitry, a data storage element coupled to the output of the asynchronous logic circuitry and a self-clocked generator. The method includes receiving input data from a previous stage data storage element; receiving, at the self-clocked generator, a previous stage active complete signal; processing the received input data through the asynchronous logic circuitry and outputting processed data; generating a current active complete signal in response to the received previous stage active complete signal and transmitting the current stage active complete signal to a next successive processing stage; and storing the processed data in a current data storage element in response to the current stage active complete signal. 
         [0016]    In another embodiment, there is provided a clock-less asynchronous processor including a plurality of processing pipelines each having a plurality of successive processing stages configured to operate asynchronously. The plurality of processing stages include a first, second and third processing stages. The first asynchronous processing stage includes first asynchronous logic circuitry configured to process first input data and output first processed data, a first data storage element coupled to the first asynchronous logic circuitry and configured to receive and store the first processed output data in response to a first stage active complete signal generated and output by a first self-clocked generator. The second asynchronous processing stage includes second asynchronous logic circuitry configured to process the first output processed data and output second processed data, a second data storage element coupled to the second asynchronous logic circuitry and configured to receive and store the second processed output data in response to a second stage active complete signal, and a second self-clocked generator configured to receive the first stage active complete signal, generate the second active complete signal in response thereto, and output the second stage active complete signal to the second data storage element. The third asynchronous processing stage includes third asynchronous logic circuitry configured to process the second output processed data and output third processed data, a third data storage element coupled to the third asynchronous logic circuitry and configured to receive and store the third processed output data in response to a third stage active complete signal, and a third self-clocked generator configured to receive the second stage active complete signal, generate the third stage active complete signal in response thereto, and output the third stage active complete signal to the third data storage element. 
         [0017]    In still another embodiment, there is provided a clock-less asynchronous circuit including asynchronous logic circuitry configured to process input data and output processed data, and further configured to perform either a first processing function associated with a first processing delay or a second processing function associated with a second processing delay. The circuit further includes a data storage element coupled to the asynchronous logic circuitry and configured to receive and store the processed output data in response to an active complete signal, and a self-clocked generator configured to: receive a trigger signal, and generate and output the active complete signal after receiving the trigger signal, the active complete signal generated and output after a predetermined time period from receipt of the trigger signal, wherein the predetermined time period is substantially equal to or greater than the first processing delay when the asynchronous logic circuitry will perform the first processing function or the predetermined time period is substantially equal to or greater than the second processing delay when the asynchronous logic circuitry will perform the second processing function. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
           [0019]      FIG. 1  illustrates a prior art asynchronous micro-pipeline architecture; 
           [0020]      FIG. 2  is a block diagram illustrating the concept of meta-stability in a synchronous system; 
           [0021]      FIG. 3  illustrates an asynchronous processing system in accordance with the present disclosure; 
           [0022]      FIG. 4  is a block diagram illustrating a single asynchronous processing stage within an asynchronous processor in accordance with the present disclosure; 
           [0023]      FIG. 5  is a block diagram of one implantation of the self-clocked generator shown in  FIG. 4 ; 
           [0024]      FIGS. 6 and 7  illustrate other implementations of the self-clocked generator shown in  FIG. 4 ; 
           [0025]      FIG. 8  is a block diagram illustrating a processing pipeline having multiple processing stages in accordance with the present disclosure; and 
           [0026]      FIGS. 9A ,  9 B and  9 C illustrate an example communication system, and example devices, in which the asynchronous processor and processing system may be utilized. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Asynchronous technology seeks to eliminate the need of synchronous technology for a global clock-tree which not only consumes an important portion of the chip power and die area, but also reduces the speed(s) of the faster parts of the circuit to match the slower parts (i.e., the final clock-tree rate derives from the slowest part of a circuit). To remove the clock-tree (or minimize the clock-tree), asynchronous technology requires special logic to realize a handshaking protocol between two consecutive clock-less processing circuits. Once a clock-less processing circuit finishes its operation and enters into a stable state, a signal (e.g., a “Request” or “Complete” signal) is triggered and issued to its ensuing circuit. If the ensuing circuit is ready to receive the data, the ensuing circuit sends a signal (e.g., an “ACK” signal) to the preceding circuit. Although the processing latencies of the two circuits are different and varying with time, the handshaking protocol ensures the correctness of a circuit or a cascade of circuits. 
         [0028]    Hennessy and Patterson coined the term “hazard” for situations in which instructions in a pipeline would produce wrong answers. A structural hazard occurs when two instructions might attempt to use the same resources at the same time. A data hazard occurs when an instruction, scheduled blindly, would attempt to use data before the data is available in the register file. 
         [0029]    With reference to  FIG. 3 , there is shown a block diagram of an asynchronous processing system  300  in accordance with the present disclosure. The system  300  includes an asynchronous scalar processor  310 , an asynchronous vector processor  330 , a cache controller  320  and L1/L2 cache memory  340 . As will be appreciated, the term “asynchronous processor” may refer to the processor  310 , the processor  330 , or the processors  310 ,  330  in combination. Though only one of these processors  310 ,  330  is shown, the processing system  300  may include more than one of each processor. In addition, it will be understood that each processor may include therein multiple CPUs, control units, execution units and/or ALUs, etc. For example, the asynchronous scalar processor  310  may include multiple CPUs with each CPU having a desired number of pipeline stages. In one example, the processor  310  may include sixteen CPUs with each CPU having five processing stages (e.g., classic RISC stages—Fetch, Instruction Decode, Execute, Memory and Write Back). Similarly, the asynchronous vector processor  330  may include multiple CPUs with each CPU having a desired number of pipeline stages. 
         [0030]    The L1/L2 cache memory  340  may be subdivided into L1 and L2 cache, and may also be subdivided into instruction cache and data cache. Likewise, the cache controller  320  may be functionally subdivided. 
         [0031]    Aspects of the present disclosure provide architectures and techniques for a clock-less asynchronous processor architecture that utilizes a configurable self-clocked generator to trigger the generation of the clock signal and to avoid meta-stability problems. 
         [0032]      FIG. 4  illustrates a portion of a processing pipeline within the asynchronous processor  310  (or  330 ). The processing pipeline will include a plurality of successive processing stages. For illustrative purposes,  FIG. 4  illustrates a single processing stage  400  within the pipeline. Each stage  400  includes a logic block  410  (or asynchronous logic circuitry), an associated self-clocked generator  420 , and a data storage element or latch (or flip-flop or register)  404 . In addition, a data latch (identified as  402 ) of a previous stage (identified as  412 ) is also shown. As will be appreciated for each stage, data processed by the respective logic block is output and latched into its respective data latch upon receipt of an active “complete” signal from the self-clocked generator associated with that stage. The logic block  410  may be any block or combination of processing logic configured to operate asynchronously as a unit or block. Some examples of such a block  410  may be an arithmetic logic unit (ALU), adder/multiplier unit, memory access logic, etc. In one example, which will be utilized hereafter to further explain the teachings and concepts of the present disclosure, the logic block  410  is a logic block configured to perform at least two different functions, such as an adder/multiplier unit. In this example, the logic block  410  has two processing time delays: the processing time required to complete the adding function and the processing time required to complete the multiplication function. In other words, the period of time between trigger and latching. 
         [0033]    Data processed from the previous stage is latched into the data latch  402  (the previous stage has completed its processing cycle) in response to an active Complete signal  408 . The Complete signal  408  (or previous stage completion signal) is also input to the next stage self-clocked generator  420  indicating that the previous stage  412  has completed processing and the data in the data latch  402  is ready for further processing by stage  400 . The Complete signal  408  triggers the self-clocked generator  420  and activates self-clocked generation to generate its own current active Complete signal  422 . However, the self-clocked generator  420  delays outputting the current Complete signal  422  for a predetermined period of time to allow the logic block  410  to fully process the data and output processed data  406 . 
         [0034]    The processing latency or delay of the logic block  410  depends on several factors (e.g., logic processing circuit functionality, temperature, etc.). One solution to this variable latency is to configure the delay to a delay value that is at least equal to, or greater than, than the worst case latency of the logic processing circuit  410 . This worst case latency is usually determined based on latency of the longest path in the worst condition. In the example of the adder/multiplier unit, the required processing delay for the adder may be 400 picoseconds, while the required processing delay for the multiplier may be 1100 picoseconds. In such case, the worst case processing delay would be 1100 picoseconds. This may be calculated based on theoretical delays (e.g., by ASIC level simulation: static timing analysis (STA) plus a margin), or may be measured during a calibration stage, of the actual logic block circuits  410 . Stage processing delay values for each stage  400  (and for each path/function in each stage  400 ) are stored in a stage clock delay table (not shown). During the initialization, reset or booting stage (referred to hereinafter as “initialization”), these stage delay values are used to configure clock-delay logic within the self-clocked generators  420 . In one embodiment, the stage delay values in the table are loaded into one or more storage register(s) (not shown) for fast access and further processing when needed. In the example of the adder/multiplier, the values 400 and 1100 (or other indicators representative of those values) are loaded into the register. 
         [0035]    During initialization, the self-clocked generator  420  is configured to generate and output its active Complete signal  422  at a predetermined period of time after receiving the previous Complete signal  408  from the previous stage  412 . To ensure proper operation (processed data will be valid upon latching) the required processing delay will equal or exceed the time necessary for the block to complete its processing. Using the same example, then when the logic block is tasked with performing an adding function, the required processing delay should equal or exceed 400 picoseconds. Similarly, when the logic block is tasked with performing an adding function, the required processing delay should equal or exceed 1100 picoseconds. The self-clocked generator  1420  generates its Complete signal  1422  at the desired time which latches the processed output data  406  of logic block  410  into the data latch  404 . At the same time, the current active Complete signal  422  is output or passed to the next stage. 
         [0036]    Now turning to  FIG. 5 , there is illustrated a more detailed diagram of the configurable or programmable self-clocked generator  420  of  FIG. 4 . The self-clocked generator  420  includes a first delay gate (or module or circuit)  502 A, a second delay gate (or module or circuit)  502 B, a first delay input multiplexor (mux)  504 A and a second delay input multiplexer  504 B. The multiplexors are configured to control an amount of delay between receipt of the previous Complete signal  408  and output (activation or assertion) of the current Complete signal  422 . Thus, the self-clocked generator  420  is configured to control/program a predetermined amount of delay (or time period). In one embodiment, the programmed period is operation dependent. 
         [0037]    A configuration parameter  510  controls operation of the multiplexors  504 A,  504 B to select a signal path for the previous Complete signal  408 . This enables selection or configuration (programming) of when the clocking signal should be issued (i.e., how much delay)—a configurable amount of delay. For example, the first delay gate  502 A may be configured to generate a signal  503  having added 500 picoseconds of delay, while the second delay gate  502 B may be configured to generate a signal  505  having added 600 picoseconds of delay, for a possible total delay of 1100 picoseconds. 
         [0038]    The configuration parameter  510  may be an N-bit select signal generated from the one or more storage registers (not shown) when the processor  310 ,  330  is initialized. Therefore, the select signal may select the first signal  503 , the second signal  505 , a combination of the first signal  503  and the second signal  505 , or virtually no delay. In this example, the current Complete signal  422  may be generated and output with 0, 500, 600 or 1100 picoseconds of delay. For example, a first configuration parameter output  512  will cause the first multiplexor  504 A to select and output either the delayed signal (500 picoseconds)  503  or the undelayed signal  408 . Similarly, a second configuration parameter output  514  will cause the second multiplexor  504 B to select and output either (1) the delayed signal  505  (which is either delayed by 500 or 1100 picoseconds), (2) the delayed signal (600 picoseconds) output from the multiplexor  504 A, or (3) the undelayed signal  408 . In general terms, the self-clocked generator  420  provides a programmable delay measured defined as the amount of time between receipt of the previous Clocking signal  408  and activation of the current Complete signal  422 . Assertion of the Complete signal  422  latches the data and further signals the data is valid and ready for next stage processing. 
         [0039]    In another embodiment, the configuration parameter  510  may generated by a controller  550 . The controller  550  determines which processing function (e.g., adding or multiplying) the logic block  410  will perform and programs the self-clocked generator  420  to generate the clocking signal  422  with the “correct” delay for that processing function. In other words, the controller  550  programs the self-clocked generator to issue its clocking signal after a predetermined processing time has passed. This predetermined processing time is defined and associated with the function to be performed. Various methods and means may be utilized to determine a priori which function will be performed by the logic block  410 . In one example, an instruction pre-decode indicates the particular processing function will be an add function or a multiply function. This information may be stored in a register or register file. Thus, the self-clocked generator  420  is programmed to generate the clocking signal  422  a predetermined amount of time after receipt of a previous clock signal (or other signal) signaling to the logic block  422  that the input data is ready for processing. This predetermined amount of time is programmed in response to a determination of what function the logic block  422  will perform. 
         [0040]    While first and second delay gates, first and second multiplexors, and first and second configuration parameters have been described in the examples above for ease of explanation, it should be appreciated that additional delay gates (and differing delay times) and multiplexors may be utilized. 
         [0041]    Now turning to  FIG. 6 , there is illustrated another implementation of the programmable delay self-clocked generator  420  having an M-to-1 multiplexer  600  with M clock input signals  620 . Similar to the configuration parameter  510 , an N-bit configuration parameter  610  (and/or a controller) controls multiplexer  600  to select one of the M clock inputs  620  for output of the current Complete signal  422 . As will be appreciated, the clock input signals  620  are generated from the previous stage Complete signal (e.g., signal  408  in  FIG. 5 ) and each are delayed by a different amount. The clock input signals are generated using any suitable configuration of clock delay gates/circuits (not shown). For example, if M=8, the eight clock input signals may be delayed in increments of 100 picoseconds beginning with 400 picoseconds. In such example, current Complete signal  422  can be selected to have a delay ranging from 400-1100 picoseconds, in increments of 100 picoseconds. It will be understood that any suitable number of clock input signals  620  and delay amounts can be configured and utilized. 
         [0042]    Now turning to  FIG. 7 , there is illustrated another implementation of the programmable delay self-clocked generator  420 . In this configuration, the self-clocked generator  420  includes a number of logic gates (as shown) and two clock input signals  702 ,  704  configured to select and output one of the clock input signals. A single Select line  720  controls which clock input signal  702 ,  704  is selected and output as the clock output signal  422  (Complete signal). 
         [0043]    Now turning to  FIG. 8 , there is illustrated a block diagram of a portion of a processing pipeline  800  having a plurality of processing stages within the asynchronous processor  310 ,  330 . As will be appreciated, the pipeline  800  may have any number of desired stages  400 . As an example only, the pipeline  800  may include 5 stages (with only 3 shown in  FIG. 8 ) with each stage  400  providing different functionality (e.g., Instruction Fetch, Instruction Decode, Execution, Memory, Write Back). Further, the processor may include any number of separate pipelines  800  (e.g., CPUs or execution units). 
         [0044]    As shown, the pipeline  800  includes a plurality of successive processing stages  400 A,  400 B,  400 C. Each respective processing stage  400 A,  400 B and  400 C includes a logic block (asynchronous logic circuitry)  410 A,  410 B and  410 C, and associated self-clocked generators  420 A,  420 B and  420 C and data latches  404 A,  404 B,  404 C. Reference is made to  FIG. 4  illustrating more details and operation of a stage  400 . 
         [0045]    As will be appreciated, each logic block  410 A,  410 B and  410 C includes asynchronous logic circuitry configured to perform one or more processing functions on the input data. When data processing is complete (i.e., sufficient time has passed to complete processing), the processed data is latched into the data storage element or flip-flop  404 A,  404 B,  404 C in response to the Complete signal  422 A,  422 B and  422 C (which also indicates to a subsequent stage that processing is complete). Each intermediate successive stage  400  processes input data output from a previous stage. 
         [0046]    The amount of processing time necessary for each logic block  410  to complete processing depends on the particular circuits included therein and the function(s) it performs. Each logic block  410 A,  410 B and  410 C has one or more predetermined processing time delays which indicate the amount of time it takes to complete a processing cycle. As previously described, stage processing delay values for each stage  400  are stored in a stage clock delay table (not shown) and may be loaded into a data register or file during initialization. 
         [0047]    For example only, the processing delays may be 500, 400 or 1100, and 600 or 800 picoseconds for stages  400 A,  400   b ,  400 C, respectively. This means that stage  400 A is either capable of performing only one function (or has only one path) or can perform multiple functions, but each function requires about the same processing delay. Stages  400 B,  400 C are capable of performing at least two functions (or have at least two paths) with each function requiring a different processing delay. 
         [0048]    Aspects of the present disclosure also provide architectures and techniques for a clock-less asynchronous processor that utilizes a first mode to initialize and set up the asynchronous processor during boot up and that uses a second mode during “normal” operation of the asynchronous processor. 
         [0049]    With continued reference to  FIG. 8 , the processor  310 ,  330  includes mode selection (and delay configuration) logic  850 . The mode selection circuit  850  configures the processor  310 ,  330  to operate in one of two modes. In one embodiment, these two modes include a Slow mode and a Fast mode. Additional modes could be configured if desired. It will be understood that the mode selection logic may be implemented using logic hardware, software or a combination thereof. The logic  850  configures, enables and/or switches the processor  310 ,  330  to operate in a given mode and switch between modes. 
         [0050]    In the Slow mode, each self-clocked generator  420 A,  420 B,  420 C is configured to generate its respective active Complete signal  422 A,  422 B,  422 C with a maximum amount of delay (which may be the same or different for each stage). In the Fast mode, each self-clocked generator  420 A,  420 B,  420 C is configured to generate its respective Complete signal  422 A,  422 B,  422 C with a predetermined (or “correct”) amount of delay (again, this may be the same or different for each stage, depending on functionality of the logic as well as different processing, voltage and temperature (PVT) corners). In general terms, the amount of delay in the Slow mode is greater than the amount of delay in the Fast mode and, therefore, the Fast mode performs processing at a faster speed. 
         [0051]    Using the example above in which the processing delays are 500, 400 or 1100, and 600 or 800 picoseconds, for stages  400 A,  400   b ,  400 C, respectively, the Slow mode will initialize or program the self-clocked generators  420 A,  420 B,  420 C for processing delays of 500, 1100 and 800 picoseconds. This ensures that each stage will be programmed with a sufficient processing delay amount to handle initialization procedures. The Fast mode enables each stage to operate in accordance with the procedures and methods described above—the processing delay for a stage will be programmed or set based on which particular function that respective logic block  410  will be performing at that time. 
         [0052]    It will be understood there may be some hardware initialization/setup sequence(s) for which it may be desirable to operate in a slower mode to properly configure the logic. During slow mode, the delay can be set relatively large to ensure logic functionality and no meta-stability. Other examples may include applications for which the circuit speed should be slowed down, such as a special register configuration or process. As will be appreciated, different asynchronous logic circuits could be switched to faster speeds globally or locally (one by one). 
         [0053]    Various factors may determine when the processor  310 ,  330  should operate in either one of the modes. These may include power consumption/dissipation requirements, operating conditions, types of processing, PVT corners, application real time requirements, etc. Different factors may apply to different applications, and any suitable determination of when to switch from one mode to another mode is within the knowledge of those skilled in the art. In other embodiments, the concepts described herein are broader, and may include switching between a first and second mode, switching between slow and fast modes, and having multiple modes (three or more). Multiple modes within normal operation may be provided, and may be implemented to vary core speeds and to adapt to different PVT or application real time requirement(s). 
         [0054]    In one embodiment, the processor  310 ,  330  is configured to operate in the Slow mode during initialization and setup (e.g., boot, reset, initialization, etc.). After initialization is completed, the processor  310 ,  330  is configured to operate in the Fast mode—which is considered “normal” operation of the processor. The mode selection and configurable delay logic  850  includes a slow mode module  812  configured to generate a maximum delay for each of the self-clocked generators  420 A- 420 C and a fast mode module  814  configured to generate a “correct” delay for each of the self-clocked generators  420 A- 420 C. The maximum delay for a given self-clocked generator may be different than the maximum delay for another one of the self-clocked generators. Similarly, the “correct” delay(s) for a given self-clocked generator may be different than the “correct” delay(s) for another one of the self-clocked generators. 
         [0055]    In one embodiment, the maximum delay for a given self-clocked generator  420  may be equal to a guaranteed delay without meta-stability+margin. For example, the configurable delay logic  850  may be configured to generate a slow mode configure signal corresponding to a slow mode delay value that is associated with a slowest speed at which the given self-clocked generator  420  can successfully process and operate. If it can perform multiple functions (or have multiple paths), the maximum processing delay for the logic block is the longest delay of the longest path of a given logic block  410  in the worst working condition. This may be measured at the wafer calibration stage for the given logic block  410  (or calculated theoretically). The configurable delay logic  850  is also configured to generate a fast mode configure signal that enables the logic block to operate in a “normal” mode—the processing delay for a stage will be programmed or set based on which particular function that respective logic block  410  will be performing at that time. Each of the self-clocked generators  420 A- 420 C is configured to generate an active Complete signal  422 A- 422 C in response to receipt of a corresponding delay configure signal  820 A- 820 C from the delay logic  850 . 
         [0056]    During initialization of the processor  310 ,  330 , the self-clocked generator  420 A may receive the delay configure signal  820 A and enter the slow mode during initialization and set up the processor. Alternatively, the self-clocked generator  420 A may enter the slow mode by default during initialization. After completion of initialization, the self-clocked generator  420 A may enter the fast mode for normal operation (in response to the delay configure signal  820 A). The other self-clocked generators  420 B,  420 C may similarly operation in response to the delay configure signal  820 B and delay configure signal  820 C. Alternatively, these self-clocked generators may enter the slow mode by default during initialization, and after initialization and set up, they may enter the fast mode during normal operation (in response to the delay configure signals  820 B,  820 C). 
         [0057]    During operation, the mode selection and configurable delay logic  850  is configured to generate a maximum delay such that asynchronous logic circuitry  410  executes in the first or slow mode during initialization. In a particular implementation, the slow mode may include a maximum delay for each of the self-clocked generators  420 A- 420 C. A first flag may be written to a register or other memory location in the processor  310 ,  330  to maintain the slow mode until initialization is complete. Thereafter, the configurable delay logic  850  configures the self-clocked generators to generate “correct” delay(s) such that the asynchronous logic circuitry  410  executes in the second or fast mode during normal operation. Thus, in the embodiment described mainly in  FIG. 8 , the programmed processing delay (or period of time between trigger and latching) is mode dependent. 
         [0058]      FIG. 9A  illustrates an example communication system  300 A that may be used for implementing the devices and methods disclosed herein. In general, the system  900 A enables multiple wireless users to transmit and receive data and other content. The system  900 A may implement one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), or single-carrier FDMA (SC-FDMA). 
         [0059]    In this example, the communication system  900 A includes user equipment (UE)  910   a - 910   c , radio access networks (RANs)  920   a - 920   b , a core network  930 , a public switched telephone network (PSTN)  940 , the Internet  950 , and other networks  960 . While certain numbers of these components or elements are shown in  FIG. 9A , any number of these components or elements may be included in the system  900 A. 
         [0060]    The UEs  910   a - 910   c  are configured to operate and/or communicate in the system  900 A. For example, the UEs  910   a - 910   c  are configured to transmit and/or receive wireless signals or wired signals. Each UE  910   a - 910   c  represents any suitable end user device and may include such devices (or may be referred to) as a user equipment/device (UE), wireless transmit/receive unit (WTRU), mobile station, fixed or mobile subscriber unit, pager, cellular telephone, personal digital assistant (PDA), smartphone, laptop, computer, touchpad, wireless sensor, or consumer electronics device. 
         [0061]    The RANs  920   a - 920   b  include base stations  970   a - 970   b , respectively. Each base station  970   a - 970   b  is configured to wirelessly interface with one or more of the UEs  910   a - 910   c  to enable access to the core network  930 , the PSTN  940 , the Internet  950 , and/or the other networks  960 . For example, the base stations  970   a - 970   b  may include (or be) one or more of several well-known devices, such as a base transceiver station (BTS), a Node-B (NodeB), an evolved NodeB (eNodeB), a Home NodeB, a Home eNodeB, a site controller, an access point (AP), or a wireless router, or a server, router, switch, or other processing entity with a wired or wireless network. 
         [0062]    In the embodiment shown in  FIG. 9A , the base station  970   a  forms part of the RAN  920   a , which may include other base stations, elements, and/or devices. Also, the base station  970   b  forms part of the RAN  920   b , which may include other base stations, elements, and/or devices. Each base station  970   a - 970   b  operates to transmit and/or receive wireless signals within a particular geographic region or area, sometimes referred to as a “cell.” In some embodiments, multiple-input multiple-output (MIMO) technology may be employed having multiple transceivers for each cell. 
         [0063]    The base stations  970   a - 970   b  communicate with one or more of the UEs  910   a - 910   c  over one or more air interfaces  990  using wireless communication links. The air interfaces  990  may utilize any suitable radio access technology. 
         [0064]    It is contemplated that the system  900 A may use multiple channel access functionality, including such schemes as described above. In particular embodiments, the base stations and UEs implement LTE, LTE-A, and/or LTE-B. Of course, other multiple access schemes and wireless protocols may be utilized. 
         [0065]    The RANs  920   a - 920   b  are in communication with the core network  930  to provide the UEs  910   a - 910   c  with voice, data, application, Voice over Internet Protocol (VoIP), or other services. Understandably, the RANs  920   a - 920   b  and/or the core network  930  may be in direct or indirect communication with one or more other RANs (not shown). The core network  930  may also serve as a gateway access for other networks (such as PSTN  940 , Internet  950 , and other networks  960 ). In addition, some or all of the UEs  910   a - 910   c  may include functionality for communicating with different wireless networks over different wireless links using different wireless technologies and/or protocols. 
         [0066]    Although  FIG. 9A  illustrates one example of a communication system, various changes may be made to  FIG. 9A . For example, the communication system  900 A could include any number of UEs, base stations, networks, or other components in any suitable configuration, and can further include the EPC illustrated in any of the figures herein. 
         [0067]      FIGS. 9B and 9C  illustrate example devices that may implement the methods and teachings according to this disclosure. In particular,  FIG. 9B  illustrates an example UE  910 , and  FIG. 9C  illustrates an example base station  970 . These components could be used in the system  900 A or in any other suitable system. 
         [0068]    As shown in  FIG. 9B , the UE  910  includes at least one processing unit  905 . The processing unit  905  implements various processing operations of the UE  910 . For example, the processing unit  905  could perform signal coding, data processing, power control, input/output processing, or any other functionality enabling the UE  910  to operate in the system  900 A. The processing unit  905  also supports the methods and teachings described in more detail above. Each processing unit  905  includes any suitable processing or computing device configured to perform one or more operations. Each processing unit  905  could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit. The processing unit  905  may be an asynchronous processor  310 ,  330  or the processing system  300  as described herein. 
         [0069]    The UE  910  also includes at least one transceiver  902 . The transceiver  902  is configured to modulate data or other content for transmission by at least one antenna  904 . The transceiver  902  is also configured to demodulate data or other content received by the at least one antenna  904 . Each transceiver  902  includes any suitable structure for generating signals for wireless transmission and/or processing signals received wirelessly. Each antenna  904  includes any suitable structure for transmitting and/or receiving wireless signals. One or multiple transceivers  902  could be used in the UE  910 , and one or multiple antennas  904  could be used in the UE  910 . Although shown as a single functional unit, a transceiver  902  could also be implemented using at least one transmitter and at least one separate receiver. 
         [0070]    The UE  910  further includes one or more input/output devices  906 . The input/output devices  906  facilitate interaction with a user. Each input/output device  906  includes any suitable structure for providing information to or receiving information from a user, such as a speaker, microphone, keypad, keyboard, display, or touch screen. 
         [0071]    In addition, the UE  910  includes at least one memory  908 . The memory  908  stores instructions and data used, generated, or collected by the UE  910 . For example, the memory  908  could store software or firmware instructions executed by the processing unit(s)  905  and data used to reduce or eliminate interference in incoming signals. Each memory  908  includes any suitable volatile and/or non-volatile storage and retrieval device(s). Any suitable type of memory may be used, such as random access memory (RAM), read only memory (ROM), hard disk, optical disc, subscriber identity module (SIM) card, memory stick, secure digital (SD) memory card, and the like. 
         [0072]    As shown in  FIG. 9C , the base station  970  includes at least one processing unit  955 , at least one transmitter  952 , at least one receiver  954 , one or more antennas  956 , one or more network interfaces  966 , and at least one memory  958 . The processing unit  955  implements various processing operations of the base station  970 , such as signal coding, data processing, power control, input/output processing, or any other functionality. The processing unit  955  can also support the methods and teachings described in more detail above. Each processing unit  955  includes any suitable processing or computing device configured to perform one or more operations. Each processing unit  955  could, for example, include a microprocessor, microcontroller, digital signal processor, field programmable gate array, or application specific integrated circuit. The processing unit  955  may be an asynchronous processor  310 ,  330  or the processing system  300  as described herein. 
         [0073]    Each transmitter  952  includes any suitable structure for generating signals for wireless transmission to one or more UEs or other devices. Each receiver  954  includes any suitable structure for processing signals received wirelessly from one or more UEs or other devices. Although shown as separate components, at least one transmitter  952  and at least one receiver  954  could be combined into a transceiver. Each antenna  956  includes any suitable structure for transmitting and/or receiving wireless signals. While a common antenna  956  is shown here as being coupled to both the transmitter  952  and the receiver  954 , one or more antennas  956  could be coupled to the transmitter(s)  952 , and one or more separate antennas  956  could be coupled to the receiver(s)  954 . Each memory  958  includes any suitable volatile and/or non-volatile storage and retrieval device(s). 
         [0074]    Additional details regarding UEs  910  and base stations  970  are known to those of skill in the art. As such, these details are omitted here for clarity. 
         [0075]    In some embodiments, some or all of the functions or processes of the one or more of the devices are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. 
         [0076]    It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. 
         [0077]    While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.