Abstract:
A DSP comprises pipeline registers, a logical operation circuit, a product-sum circuit, DSP registers and an interface. The DSP registers includes at least a plurality of program control registers and excludes the pipeline registers, the logical operation circuit, the product-sum circuit. The interface is connected to the DSP registers, and causes an external device to be capable of writing and reading out from the DSP registers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a digital signal processor (hereafter referred to as the DSP) including a logical operation circuit, a product-sum circuit, and registers. 
     The present application is based on Japanese Patent Application No. 2000-066536, which is incorporated herein by reference. 
     2. Description of the Related Art 
     The DSP includes a logical operation circuit, a product-sum circuit, and registers, adopts the so-called harbored architecture and a structure capable of program control for repetitive operation processing, and is widely used as it is optimal in continuous product-sum operation processing by an FIR filter (i.e., finite impulse response filter) or the like. 
       FIG. 1  shows a typical example of a related DSP. The DSP is comprised of a product-sum circuit (including pipeline registers, a multiplier, a bit expander, adders, and a limiter) including pipeline registers and adders for effecting pipeline processing of data, a logical operation circuit (including a logic), and registers (registers and product-sum memories MACH and MACL), and data memories (data memories X and Y) and an instruction memory are connected thereto. 
     For example, as shown in  FIG. 2 , a host computer  1  sets data necessary for operations in the aforementioned data memories (data memories X and Y)  4   a  and  4   b  through a PCI bus interface  2  and a local bus interface  3 , causes a DSP  6  to perform operations, and obtains their results through the memories  4   a  and  4   b.    
     A program necessary for DSP operations is set in an instruction memory  5 . The DSP  6  advances the program step of the instruction memory by a program counter in the internal registers. 
     However, in control using the above-described DSP, the host computer  1  basically merely inputs data necessary for operations to the DSP and sends control signals for starting or stopping the operation, while the DSP merely delivers the results of operation by handshaking with respect to those signals, and the DSP itself is merely designed to specifications for performing stand-alone operations. Accordingly, the host computer, when performing the DSP operation, is able to obtain only the results of operation by the DSP operation, and is unable to execute detailed processing routines which are not predetermined routine operations, so that there has been a drawback in that the scope of application is limited. 
     In addition, since it is impossible to directly access the internal registers, it has been necessary to separately provide a test circuit for the registers inside the DSP. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to enhance control functions from outside the DSP. 
     To overcome the above-described problems and achieve the above object, according to a first aspect of the present invention, there is provided a digital signal processor which comprises a logical operation circuit, a product-sum circuit, a plurality of registers, and an interface capable of allowing access to the registers from an external device. 
     In the first aspect of the present invention, the logical operation circuit and the product-sum circuit may be circuits, which are to be used in an ordinary DSP, and for example, which are to be located below the pipeline register, 32bitX2, 18bit, in  FIG. 1 . The registers refer to those other than the same. In the present invention, there is provided an interface capable of allowing direct access to the registers in the DSP from a host computer side. The interface capable of allowing direct access, means that reading-out and writing are possible with respect to the registers from an external device at arbitrary timings. Accordingly, the following things become possible. 
     (a) Since direct access to the registers from an external device, i.e., a host computer side, is possible, the program sequence of the DSP can be controlled from the host computer. 
     (b) Even if a test circuit is not provided in the DSP, it is possible to test the registers from the external host computer or tester. For this reason, the testability of the DSP is high. 
     (c) It is possible to execute not only predetermined arithmetic routines of the DSP but also detailed processing routines. 
     (d) It is possible to interconnect DSPs. 
     Further, according to a second aspect of the present invention, the registers may be program control registers including at least a program counter and an interrupt vector. 
     In the second aspect of the present invention, at least registers that can be directly accessed, are the aforementioned program control registers. Accordingly, it is impossible to access the pipeline registers, general purpose registers, product-sum registers, and the like. Since these registers are used for arithmetic operations, it can be said that the need for accessing them from the host computer is not so large. 
     Taking the above into consideration, according to a third aspect of the present invention, the interface is directly connected to the registers, and causes an external device to be capable of writing and reading out from the registers, so that direct access to the registers from the external device is established through the interface. 
     Further, according to a fourth aspect of the present invention, the interface is connected to one of control registers provided in a local bus interface and a local bus. 
     Further, according to a fifth aspect of the present invention, the program control registers may include both of the program counter and the interrupt vector. 
     Furthermore, according to a sixth aspect of the present invention, the registers can be tested by an external device without provision of a test circuit in the DSP discussed above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a related DSP; 
         FIG. 2  is a diagram of a system using the related DSP; 
         FIG. 3  is a diagram of a system using a DSP of a preferred embodiment according to the present invention; 
         FIG. 4  is a diagram of the DSP of the embodiment according to the present invention; 
         FIG. 5  is a diagram illustrating registers; 
         FIG. 6  is a diagram listing names of host interface terminals; 
         FIG. 7  is a diagram listing names of a system interface; and 
         FIG. 8  is a diagram of interconnection of DSPs and a computation sequence diagram. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 3  shows a system configuration using the DSP in accordance with an embodiment of the present invention. A host computer  1  sets data necessary for operations in the aforementioned data memories (data memories X and Y)  4   a  and  4   b  through a PCI bus interface  2  and a local bus interface  3 , causes a DSP  6  to perform operations, and obtains their results through the memories  4   a  and  4   b . A program necessary for DSP operations is set in an instruction memory  5 . The DSP  6  advances the program step of the instruction memory by a program counter in the internal registers. 
     When the DSP  6  is made to perform, for example, a filtering operation, a coefficient (a coefficient address in a case where a coefficient table is present in the DSP) and data are input to the DSP  6  from the host computer  1  to send an operation-start control signal (operation start signal). At the time of completion of the filtering operation, an operation-end control signal (operation stop signal) is sent to the DSP  6  from the host computer  1 . Further, a reset signal for initializing the DSP  1  and an interrupt request signal are also sent. 
     The PCI bus interface  2  serves as an interface with a PCI bus to which the host computer  1  is connected, while the local bus interface  3  serves as an interface between the PCI bus and the DSP  6 . In the DSP  6  in this embodiment, registers  6   a  inside the DSP (hereafter, the DSP registers  6   a ) and the local bus interface  3  are directly connected through an interface inside the DSP and a line  8   b . It should be noted that a line  8   a  does not show that the registers are directly connected, but shows that control registers  3   a  of the local bus interface  3  are mapped at addresses of data memories  4 . Accordingly, it is possible for the host computer  1  to directly access the DSP registers  6   a.    
     The DSP registers  6   a  in this embodiment are formed by program control registers including a program counter and an interrupt vector. Although other registers may be included, pipeline registers used in DSP operations are not included. 
       FIG. 4  is a schematic diagram of the DSP. 
     In this DSP  6 , an interface  6   b  is connected to the DSP registers  6   a . Referring also to  FIG. 3 , the interface  6   b  is connected through the lines  8   a  and  8   b  to the control registers  3   a  in the local bus interface  3  or to a local bus  7 . As shown in  FIG. 5 , the DSP registers  6   a  include at least program control registers including an instruction fetch register, a program counter, a program stack, an interrupt vector, a loop start address register, a loop end address register, and a loop counter. In this embodiment, although general purpose registers and index registers for the data memories  4   a  and  4   b  are additionally included, these registers need not necessarily be made accessible. 
       FIG. 6  is a terminal diagram of the above-described interface  6   b . Terminals in the drawing are referred to as host interface terminals. A method of accessing the registers using these terminals is as follows. 
     Access (Reading Out) from the Host Computer to the DSP Registers 
     An address of a DSP register to which read access is to be made is set for a host address terminal (i — Host — address), and a host read request is sent to a host read terminal (i — Host — read). At this time, data on the aforementioned DSP register is read and carried on a host input/output terminal (i — Host — data). 
     Access (Writing) from the Host Computer to the DSP Registers 
     An address of a DSP register to which write access is to be made is set for the host address terminal (i — Host — address), and a host write request is sent to a host write terminal (i — Host — write). At this time, data is carried on the host input/output terminal (i — Host — data), and this data is written in the aforementioned DSP register. 
     By providing the above-described configuration, by changing on the host computer side an initial value of a loop start address register or an initial value of the program counter, the contents of operation in the DSP  6  can be changed. In addition, it is possible to set an initial address of certain processing in the program counter, and then to issue a start request to the DSP. This means that only a part of the DSP program becomes usable on the host computer  1  side. By using this function, the DSP  6  can be used not only as a stand-alone, but also as a coprocessor for the host computer. Thus, as the host computer  1  accesses the program control registers in the DSP registers  6   a  and effects reading out and writing, and the program sequence of the DSP  6  can be simply controlled by the host computer  1 , thereby making it possible to render the form of usage of the DSP very wide. 
     In addition, as a test is connected to the DSP registers, it is possible to effect reading out and writing by directly accessing the registers from the tester, so that testing of the internal registers of the DSP can be performed easily. Accordingly, a special test circuit is not required in the DSP. As a result, testability improves easily. 
       FIG. 7  shows a diagram of ordinary DSP terminals (system interface terminals). As shown in the drawing, since the ordinary DSP terminals have only those terminals to which requests such as a start request (i — start), a stop request (i — halt), an interrupt request (i — interrupt), and the like are issued from the host computer side, only the starting and stopping of predetermined arithmetic programs of the DSP can be effected. 
     In accordance with the configuration of the DSP in this embodiment, an interconnection between DSPs is possible, and one DSP can be provided with a host function.  FIG. 8  shows an example in which two DSPs  6 ( 1 ) and  6 ( 2 ) are interconnected to form an FIR filter computing unit. In this example, a result of FIR filter computation by the DSP  6 ( 1 ) using data  1  and a coefficient 1 is further subjected to FIR filter computation by the DSP  6 ( 2 ) using a coefficient 2. In addition, one DSP  6 ( 1 ) is provided with a host function. It should be noted that times 1T, 2T, 3T, . . . , denote sampling times, and each DSP effects a convolution operation (product-sum operation) within each sampling section. 
     An outline of the procedures of the DSP  6 ( 1 ) are as follows. 
     Procedure 1: execution of the computation of a T section by the DSP  6 ( 1 ) 
     Procedure 2: confirmation of the completion of computation by the DSP  6 ( 2 ) 
     Procedure 3: copying of the result of computation by the DSP  6 ( 1 ) to data  2   
     Procedure 4: writing of necessary control information in the registers of the DSP  6 ( 2 ) 
     Procedure 5: issuance of an operation start request to the DSP  6 ( 2 ) 
     Procedure 6: return to procedure 1 
     In the above-described procedures, the operation of procedure 4 provides access to the registers of the DSP  6 ( 2 ). 
     By interconnecting the DSPs  6  in the above-described manner, it is possible to allow product-sum operations of the DSPs to be effected in parallel and to provide one DSP  6  with a host function. 
     In accordance with the present invention, the following advantages are obtained. 
     Since it is possible for the host computer side to directly access the registers, it is possible to control the program sequence of the DSP from the host computer. For example, it is possible to change an initial value of a loop program of the DSP program or change a value of the program counter so as to issue an operation start signal. In addition, this function makes it possible to interconnect the DSPs and to use one DSP as the host. 
     Even if a test circuit is not provided in the DSP, it is possible to test the internal registers of the DSP from an external device. For this reason, the testability of the DSP becomes high.