MASTER SLAVE MICROPROCESSOR SYSTEM WITH VIRTUAL MEMORY

Abstract: A microprocessor device having a virtual storage system and comprising: a master microprocessor including a bus control unit for controlling the status of a bus, an instruction decoder for dec­ oding instructions for the master microprocessor and an op­ eration execution unit for executing operation designated by the instructions for the master microprocessor with data and/­ or information stored in the memory location indicated by said instructions; a slave microprocessor being controlled by the master microprocessor to execute the operation designated by in­ structions for the slave microprocessor, and including an in­ struction decoder for decoding the instructions for the slave microprocessor and an operation execution unit for execut­ ing the operation designated thereby with data and/or in­ formation stored in the memory location indicated by said instructions for the slave microprocessor; a main storage for storing information and data for the master microprocessor and the slave microprocessor; an external storage associated to the main storage for storing information and data for the master microprocessor and/or the slave microprocessor; and a bus coupling the master microprocessor, the slave mic­ roprocessor and the main storage to each other so as to transfer data and information to each other; the microprocessor device further comprising: means for detecting whether or not the memory location required by a certain instruction is physically present in the main storage, said detecting means being mounted in the master microprocessor and associated to the bus control unit for enabling access to the main storage or for generating an interrupt to transfer information and/or data from the ex­ ternal storage to the main storage, in accordance with the content of the instruction; and means for feedbacking to the master microprocessor the decoded instruction for the slave microprocessor which in­ cludes address which is not physically present in the main storage, so as to be processed by the detecting means.

Description: Background of the Invention Field of the Invention The present invention relates to microprocessor device having a virtual storage system therein, more specifically to a control system for controlling a slave processor which is connected to the external part of a microprocessor to execute a portion of an instruction set. Description of the related art There exists a limit on the number of devices which can be integrated in a one-chip microprocessor composed of a large scale integrated circuit (LSI). It is, therefore, difficult for a single one-chip microprocessor to execute high level instructions such as floating point arithmetic at high speed. This is why an instruction set is classified into two kinds, each of which is executed in a master processor and a slave processor respectively. A master processor is a processor which can operate as a central processing unit (CPU) independently of the slave processor. A slave processor is a processor which executes instructions in place of a master processor under control thereof. Such a slave processor executes mainly high level instructions such as floating point arithmetic. By connecting a slave processor to a computer system in which a master processor operates as CPU, user can expand the instruction set. Intel 8086 and Intel 8087 are the master processor and slave processor composed of a one-chip LSI respectively. A conventional microprocessor device comprises a master processor, a slave processor and a main storage. The master processor and the slave processor share an address/data common bus and a control bus to access the main storage. Addresses and data by which the master processor or slave processor accesses the main storage are transmitted in time division through the address/data common bus. A handshake signal line is connected between the master processor and the slave processor. The master processor, moreover, supplies an instruction decode condition signal to the slave processor so that instructions can be decoded simultaneously in both processors. Instruction set executed by the above microprocessor system is classified into instructions for master processor and instructions for slave processor. Instructions for master processor are the instructions by which the master processor executes operation and accesses the main storage. The slave processor supervises the address/data common bus and the control bus, and fetches instructions simultaneously with the master processor. The slave processor, furthermore, decodes the instructions for master processor simultaneously with the master processor, in response to the decode condition signal from the master processor. The slave processor, however, does not execute the operation. Instructions for slave processor are the instructions by which the slave processor executes operation. The master processor deals with a group of instructions for slave processor as a single instruction (hereinafter referred to as "ESC instruction"). The slave processor supervises the address/data common bus and the control bus, and fetches instructions simultaneously with the master processor. The slave processor, furthermore, decodes the instructions for slave processor simultaneously with the master processor in response to the decode condition signal and execute the same. Operation of the master processor and the slave processor with the instructions for slave processor depends on presence of memory operand and on whether the memory operand is to be read or written. (1) In case there does not exist memory operand The master processor does not execute the instructions. The slave processor executes the operation designated by the instruction for the internal register operand. (2) In case there exists memory operand The master processor calculates the operand address and drives the bus cycle to read one word of first address (for example 16 bits) out of the main storage. The slave processor supervises the address/data common bus and the control bus, and reads first address of the operand and data by one word and stores them when the master processor drives the read bus cycle. The operation of the slave processor thereafter is classified into three cases depending on the reading and writing conditions. (2-1) In case of reading the memory operand of one word The slave processor executes the operation designated by the instruction for the memory operand of one word read in and the internal register operand if necessary, and stores the operation result in the internal register. (2-2) In case of reading the memory operand of more than two words The slave processor obtains the right to use the address/data bus and the control bus from the master processor in response to the handshake signal. The slave processor drives the read bus cycle by itself to read the remainder of the memory operand. Then the slave processor executes the operation designated by the instruction for the read out memory operand and the internal register operand if necessary, and stores the operation result in the internal register. (2-3) In case of writing to the memory operand The slave processor executes the operation designated by the instruction for the internal register operand. Then the slave processor obtains the right to use the address/data bus and the control bus from the master processor in response to the handshake signal, and writes the operation result to the memory operand. The above-mentioned conventional microprocessor system does not support the virtual storage. As a microprocessor becomes of higher performance, more demand is raised for the virtual storage which provides virtually bulk storage by using the external storage besides the main storage of the limited memory, especially the virtual storage of paging method. In the virtual storage of paging method, the address space which the programmer imagines (virtual address space) is divided into pages of several thousand bytes, and the address space is mapped to the address space of the main storage (real address space) page after page. The page which is mapped to the real address space is a portion of all the pages in the virtual address space, and the remainder is undefined or exists in an external storage. In the virtual storage of paging method, memory is protected by adding an attribute indicating whether reading out of or writing to the storage can be or cannot be executed to every page. In a microprocessor supporting the virtual storage of paging method, the following three checks are thus required in case of accessing the memory operand. (I) Paging over check In paging over check, it is checked whether the memory operand is included in a single page, or included over two successive pages. In case the memory operand is included over two successive pages (paging over), address mapping check and memory protect check described hereinafter are carried out on the second page as well. In carrying out the paging over check, information is required on the first address and the data length of the memory operand. (II) Address mapping check In address mapping check, it is checked whether the page indicated by the virtual address exists in the main storage (real address space) or in the external storage after the address mapping from the virtual address to the real address is executed. In carrying out the address mapping check, information is required on the virtual address of the page including the memory operand. (III) Memory protect check In memory protect check, it is checked whether or not it is allowed to access the page including the memory operand. In carrying out the memory protect check, information is required on the virtual address of the page including the memory operand and on whether reading or writing takes place for the memory operand. To utilize the property of software executed by the master processor and slave processor which do not support the virtual storage effectively, the master processor and slave processor supporting the virtual storage have to be able to execute the same instruction set as conventional one. In forming a master processor in which the above address mapping system and memory protect system are incorporated in a LSI chip in order to support the virtual storage of paging method, the conventional control system has the following disadvantages and cannot control the slave processor in a right way. - Disadvantage 1 - It is necessary for the master processor to recognize whether the memory operand is to be read or written in order to execute the memory protect check using a memory protect system incorporated in the master processor. In case of executing instructions for slave processor by the conventional system, the slave processor can judge whether the memory operand is to be read or written through decoding, but the master processor does not decode such instructions and thus cannot execute the memory protection check. - Disadvantage 2 - To carry out the paging over check for the memory operand, information is required not only on the first virtual address of the operand but also on the data length of the operand. In case of executing instructions for slave processor by the conventional system, the master processor cannot execute the paging over check because the master processor cannot recognize the data length of the memory operand. On the contrary, the slave processor can execute the paging over check but does not have means for executing address mapping check and memory protect check on the second page making use of the address mapping system and the memory protect system inside the master processor in case that the memory operand is included over two successive pages. - Disadvantage 3 - Once it is clarified that the memory operand does not exist in the main storage but in the external storage through the address mapping check executed, the master processor stops execution of the instruction and transmits the page including the memory operand from the external storage to the main storage. Then the master processor has to execute again the instruction stopped on the way. The slave processor has, however, already started execution of instructions for slave processor just after the master processor finishes decoding ESC instructions in the conventional system. It is not, therefore, possible to carry out the correct address mapping check. Above disadvantages are all concerned about the virtual storage, but there exist some other disadvantages as follows: - Disadvantage 4 - In case of using a master processor having an address bus and a data bus independent to each other instead of a common bus transmitting addresses and data in time division, the number of the external pins of the slave processor LSI increases because an address bus and a data bus are provided independently to each other in the slave processor as well. - Disadvantage 5 - As mentioned above, the slave processor supervises the address/data common bus and control bus, and executes instruction fetching and instruction decoding simultaneously with the master processor. It is, however, necessary to supply instruction decode condition signals to the slave processor, in the master processor in which the multistage pipelining is executed. The number of the external pins, therefore, increases furthermore both in the master processor LSI and the slave processor LSI. A control system according to the preamble of claim 1 is disclosed in US-A-4 547 849. This document deals with the same problems as mentioned above and presents a solution in which the ability of the slave to drive the bus is taken away and all operand/result accesses are accomplished via the master processor. In this control a relatively extensive decoding of the ESC instructions is carried out by the master processor, wherein the potential length of the operand/result being determined in this decoding. Accordingly, it is an object of the present invention to provide a microprocessor device in which a master processor can execute memory protection check. Another object of the present invention is to provide a microprocessor device in which a master processor can execute paging over check and a slave processor can execute address mapping check and memory protection check on the second page in case of paging over. Still another object of the present invention is to provide a microprocessor device in which a slave processor can execute address mapping check properly even after the slave processor starts to execute instructions for slave processor. Still another object of the present invention is to provide a microprocessor device in which a master processor LSI and a slave processor LSI have a small number of the external pins. These objects are achieved by a control system having the features of claim 1; the dependent claims are related to further developments of the invention. According to an preferred embodiment of the present invention, the whole memory locations of the main storage and the external storage are mapped into virtual memory of paging method, and the instructions are assigned with virtual address. According to an embodiment of the present invention, the detecting means comprises: an effective address calculation unit coupled to the bus control unit and for calculating the effective address of the memory location required by the instruction and executing the paging over check; a store management unit coupled to the effective address calculation unit and for mapping the memory location required by the instruction into physicl address in the main memory or I/O address. The control system of the present invention may comprise an address decoder coupled between the bus control unit and the second microprocessor and for generating a select signal in response to the status of the signal outputted from the bus control unit. According to an embodiment of the present invention, the address decoder is adapted to receive from the bus control unit a signal indicating the effective address of the main storage or I/O address and to output a select signal in response to the I/O address. On the other hand, the feedbacking means may include: a command port coupled to the bus and operative to read instructions for the second microprocessor out of the bus in response to a control signal given by the first microprocessor, so that the instruction decoder of the second microprocessor being adapted to receive the output of the command port and operative to decode only the instructions for the second microprocessor; and a feedback port being coupled to the instruction decoder of the second microprocessor to receive the decoded instructions for the second microprocessor, and operative to store the information out of the instruction decoder temporarily and feedback the stored information to the first microprocessor in response to a control signal given by the first microprocessor. The feedback means may further include: a decoder being coupled to the address decoder and operative to decode the select signal and output a control signals for controlling the second microprocessor and the feedback means. Such control signals outputted from the decoder may include: a starting signal to an operation execution unit of the second microprocessor; a read control signal to the feedback port, and a write control signal to the command port. According to a preferred embodiment of the present invention, the first microprocessor is composed of a one-tip large scale integrated circuit in which the detecting means is incorporated. The second microprocessor is preferably composed of a one-chip large scale integrated circuit in which the feedback means is incorporated. The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiment of the invention with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is a block diagram of a conventional microprocessor device, and Figure 2 is a block diagram of a control system for a microprocessor device in accordance with the present invention. Description of the Preferred Embodiment Referring to Figure 1, a conventional microprocessor device will be explained. The microprocessor device shown in Fig. 1 comprises a master processor 1, a slave processor 2 and a main storage 3, which are coupled to each other by address/data common bus 4 and a control bus 5. Addresses and data by which the master processor 1 or the slave processor 2 accesses the main storage 3 are transmitted in time division through the address/data common bus 4. A handshake signal line 6 is connected between the master processor 1 and the slave processor 2 so that the slave processor 2 operates in response to the handshake signal. The master processor 1, moreover, supplies an instruction decode condition signal 7 to the slave processor 2 so that instructions can be decoded simultaneously in both processors. The microprocessor system executes an instruction set including instructions for master processor and instructions for slave processor. Instructions for master processor are the instructions by which the master processor 1 executes operation and accesses to the main storage 3. The slave processor 2 supervises the address/data common bus 4 and the control bus 5, and fetches instructions simultaneously with the master processor 1. The slave processor 2, furthermore, decodes the instructions for master processor simultaneously with the master processor 1 in response to the decode condition signal 7 from the master processor. For these instructions, however, the slave processor 2 does not execute operation. Instructions for slave processor are the instructions by which the slave processor 2 executes operation. The master processor 1 deals with a group of instructions for slave processor as "ESC instruction". The slave processor 2 supervises the address/data common bus 4 and the control bus 5, and fetches instruction simultaneously with the master processor 1. The slave processor 2, furthermore, decodes and executes instructions for slave processor in response to the handshake signal 6. Turning to Figure 2, there is shown a microprocessor device in accordance with the present invention. The microprocessor device shown in Fig. 2 comprises a master processor 10 including a hardware for supporting the virtual storage and a slave processor 20 which is controlled by the master processor 10. Both processors 10 and 20 are composed of one-chip LSI and execute high level operations jointly with another. The microprocessor device further includes a main storage 30 which stores programs and data for the master processor 10 and the slave processor 20. An external storage 31 is provided and associated to the main storage 30. The main storage 30 is necessarily accessed by the master processor 10. The microprocessor device further includes an address decoder 50 which executes I/O mapping of the slave processor 20 to the master processor 10 so that data and status information are transferred to the slave processor 20. The master processor 10 includes an instruction decoder 11. The instruction decoder 11 is coupled to an effective address calculation unit 12 which receives the output of the instruction decoder 11 and executes address calculation therefrom. The effective address calculation unit 12 is coupled to a storage management unit 13. The storage management unit 13 receives the virtual address from the effective address calculation unit 12 and executes mapping thereof to the real address and simultaneously executes the memory protection check. The storage management unit 13 thus supports the virtual storage of paging method. The instruction decoder 11 is coupled also to an operation execution unit 14. The operation execution unit 14 executes the operation designated by the instruction for master processor. The storage control unit 13 is coupled to a bus control unit 15. The bus control unit 15 drives an address bus 41 and a control bus 42, and executes sending data to and receiving data from the slave processor 20 or the main storage 30 through a data bus 40. Thus the data bus 40 is shared by the master processor 10 and the slave processor 20 to access the main storage 30, The address bus 41 couples bus control unit 15 with an address decoder 50, and transmits the real address or the I/O address to the address decoder 50. The control bus 42 couples the bus control unit 15, the main storage 30 and the address decoder 50 to each other. The control bus 42 transmits information indicating the data sender and the data receiver on the data bus 40 and information indicating the timing of the bus cycle. The address decoder 50 outputs a select signal 43 to the slave processor 20 in response to the control bus signal. The slave processor 20 includes a decoder 25 which receives the select signal 43 and decodes the same. The decoder 25 outputs at least a write control signal 26 to the command port 21, a read control signal 27 to the feedback port 23 and a starting signal 28 to the operation execution unit 24. The slave processor 20 includes a command port 21. The command port 21 is coupled to the data bus 40 so that instructions for slave processor are written to the command port 21 under the instruction of the master processor 10 as described hereinafter. The command port 21 is associated to an instruction decoder 22. The instruction decoder 22 is an executive instruction decoder for instructions for slave processor. The instruction decoder 22 is coupled to an feedback port 23 to output the decoded instruction. The feedback port 23 temporarily stores the information indicating the data length of the memory operand outputted by the instruction decoder 22 and the information on reading or writing. The feedback port 23 is coupled to the data bus 40 so that the stored information is transmitted to the master processor 10 through the data bus 40. The instruction decoder 22 is also coupled to an operation execution unit 24 to output the decoded instruction thereto. The operation execution unit 24 is coupled to the data bus 40 and executes instructions for slave processor. The processing process for executing instructions for master processor and for slave processor will be described hereinafter with reference to Figure 2. (a) Execution of instructions for master processor The instruction for master processor read out of the main storage 30 is decoded by the instruction decoder 11 in the master processor 10. The operation is executed by the operation execution unit 14. In case a memory operand is included in the instruction, the virtual address is calculated by the effective address calculation unit 12 and the calculated virtual address is mapped to the real address by the storage management unit 13. The real address is outputted and transmitted to the main storage 30 through the bus control unit 15. Thus sending and receiving operand is exchanged between the operation execution unit 14 and the main storage 30 to execute the instruction. The paging over check is executed by the effective address calculation unit 12 simultaneously with execution of the virtual address calculation. On the other hand, address mapping check and memory protection check are executed by the storage management unit 13 simultaneously with execution of mapping to the real address. In this case, the above checks are executed on the second page if the memory operand is included over two successive pages. Thus executing of address mapping check and memory protection check clarifies whether or not it is possible to access the main storage. Read/write to the main storage can be executed if it is possible to access the main storage. If it is not possible to access the main storage, no operation is executed in the operation execution unit 14 and the internal interruption (exception) occurs in the master processor 10. If the page including the memory operand exists in an external storage (not shown in the drawings), the page is transmitted to the main storage by the exception processing program. Then the instruction decoding operation on the instruction concerned about the above exception will be executed again. During this period, the slave processor 20 starts no processing at all because the select signal 43 of the slave processor 20 is not effective. (b) Instruction for slave processor The master processor 10 deals with a group of instructions defined as instructions for slave processor as a single instruction (ESC instruction). If the instruction decoder 11 of the master processor 10 finds the given instruction the ESC instruction by decoding, the operation execution unit 14 controls the bus control unit 15 to write an instruction code of the ESC instruction to the I/O address in which the command port of the slave processor 20 is mapped. The select signal 43 from the address decoder 50 and the command port write control signal 26 from the decoder 25 are turned active, and then the instruction code on the data bus 40 is written to the command port 21 and the instruction decoder 22 decodes the instruction for slave processor. The operation execution unit 24 of the slave processor 20, however, has not started its execution yet at this point of time. The processing of the master processor 10 and the slave processor 20 after the above-mentioned processing depends on the presence of the memory operand. (b-1) In case there exists no memory operand In the master processor 10, the operation execution unit 14 controls the bus control unit 15 to drive I/O bus cycle. As a result, the starting signal 28 of the operation execution unit 24 becomes active. The operation execution unit 24 starts execution in response to the active starting signal 28 with the internal register operand thereof. (b-2) In case there exists memory operand The operation execution unit 14 controls the bus control unit 15 so that the master processor 10 reads out the I/O address to which the feedback port 23 is mapped. Thus the master processor 10 recognizes the data length of the memory operand and whether the memory operand is to be read or written. The virtual address calculation and paging over check are executed by the effective address calculation unit 12. Address mapping check and memory protection check (on the second page as well in case of paging over) are executed by the storage management unit 13. In case the memory operand exists in the main storage and it is possible to access the memory operand, the master processor 10 drives the I/O bus cycle again and the starting signal 28 of the operation execution unit 24 is turned active. In case the page including the memory operand exists in the external storage, the master processor 10 executes an exception to transmit the page to the main storage from the external storage. The operation execution unit 24 of the slave processor 20, however, has not yet started the operation because the starting signal 28 remains inactive. The instruction for slave processor thus can be executed again in a right way. The processing of the master processor 10 and the slave processor 20 after the above processing is classified into two ways. (b-2-1) In case of reading the memory operand The master processor 10 drives the bus cycle in which the memory operand is transmitted from the main storage 30 to the slave processor 20. The operation execution unit 24 of the slave processor 20 starts the operation in response to the starting signal 28. The operation execution unit 24 executes the operation designated by the instruction with the memory operand read out and if necessary the internal register operand thereof, and store the operation result in the internal register. (b-2-2) In case of writing to the memory operand The operation execution unit 24 of the slave processor 20 executes the operation designated by the instruction with the internal register operand in response to the starting signal 28. The master processor 10 drives the bus cycle in which the operation result is transmitted from the slave processor 20 to the main storage 30. As above described, the control system for the microprocessor device according to the present invention comprises, means for feedbacking the output of the instruction decoder of the slave processor to the master processor; and means for controlling the start of instruction decoding of the slave processor and the start of the operation executing respectively by the master processor. On this viewpoint, the microprocessor device has the following three advantages. (1) The virtual storage can be supported with instructions for slave processor in the master processor including the virtual storage of paging method. (2) The scale of the instruction decoder in the master processor and the slave processor becomes smaller. It is not necessary to decode the data length of the memory operand and whether the memory operand is to be read or written because the master processor can deal with a group of instructions for slave processor as a single instruction. On the other hand, it is not necessary to decode instructions for master processor in the slave processor. (3) The slave processor capable of executing different groups of instruction can be associated to the master processor. It is possible to define the data length of the memory operand and the read/write condition in the slave processor, if the instructions are conformed to the instruction format as the group of instructions for slave processor. In the microprocessor device of the present invention, the slave processor operates under control of the master processor only and does not execute data transmitting. The following two advantages are obtained from the above feature of the device. (4) The number of the external pins of the master processor LSI and the slave processor LSI can be decreased. Since the decode condition signal is not required in the master processor, the number of the external pins for the address bus is decreased to a great extent in the slave processor. (5) The scale of the hardware of the slave processor can be made smaller. The slave processor needs not drive the address bus and the control bus, and does not execute the instruction fetching and instruction decoding simultaneously with the master processor.

Claims: A control system for a microprocessor system, said microprocessor system including a first microprocessor (10), a second microprocessor (20) controlled by the first microprocessor to execute the operation of a portion of the instruction set of said microprocessor system, a main storage (30) for storing data for the first microprocessor and the second microprocessor, an external storage (31) associated to the main storage for storing data for the first microprocessor and/or the second microprocessor, and a bus (40) coupling the first microprocessor, the second microprocessor and the main storage to each other so as to transfer data to each other; the first microprocessor including a bus control unit (15) for controlling the status of the bus with respect to the second microprocessor and the main storage, an instruction decoder (11) for decoding instructions for the first microprocessor and detecting whether or not a given instruction is directed to the second microprocessor, and an operation execution unit (14) for executing instructions for the first microprocessor with data stored in the memory location indicated by the instruction, the first microprocessor operating, when the instruction decoder detects that the given instruction is directed to the second microprocessor, to cause the second microprocessor to read the given instruction directed to the second microprocessor, from the bus, and to decode the same given instruction; the second microprocessor including an instruction decoder (22) for decoding only instructions for the second microprocessor and an operation execution unit (24) for executing the same with data stored in the memory location indicated by the instruction; characterized in that the control system comprises : Means (23) coupled to the instruction decoder of the second microprocessor and operating to feedback information concerning the length of the memory operand and whether the access is read or write to the first microprocessor, and means (12, 13, 14, 15) receiving information from the feedback means and from said instruction decoder (11) of said first microprocessor (10) for detecting the memory location required by the given instruction directed to the second microprocessor and whether it is physically present in the main storage or not, before execution of said given instruction by the second microprocessor, said detecting means being mounted in the first microprocessor and associated to the bus control unit for enabling access to the main storage when the memory location required by said given instruction directed to the second microprocessor is physically present in the main storage, said detecting means operating, when the memory location required by said given instruction directed to the second microprocessor is not physically present in the main storage, to generate an interrupt to transfer data from the external storage to the main storage, and to control the second microprocessor so as to cause the second microprocessor to start to execute the given instruction only after said data is transferred from the external storage to the main storage thereby accommodating the possibility of invalid accesses. A control system as claimed in claim 1 wherein the whole memory locations of the main storage (30) and the external storage (31) are mapped into virtual memory of paged type, and the instructions operate with virtual addresses. A control system as claimed in claim 2 wherein the detecting means comprises: An effective address calculation unit (12) coupled to the bus control unit (15) and for calculating the effective address of the memory location required by the instruction and executing a paging over check; a store management unit (13) coupled to the effective address calculation unit (12) and for mapping the memory location required by the instruction into physical address in the main memory or I/O address. A control system as claimed in claim 1 , further comprising an address decoder (50) coupled between the bus control unit (15) and the second microprocessor (20) and for generating a select signal in response to the status of the signal outputted from the bus control unit. A control system as claimed in claim 4 wherein the address decoder (50) is adapted to receive from the bus control unit (15) a signal indicating the effective address of the main storage or I/O address and output a select signal in response to the I/O address. A control system as claimed in claim 1 wherein the feedbacking means includes: A command port (21) coupled to the bus and operative to read instructions for the second microprocessor out of the bus in response to a control signal given by the first microprocessor (10), with the instruction decoder (22) of the second microprocessor (20) being adapted to receive the output of the command port (21) and operative to decode only the instructions for the second microprocessor; and a feedback port (23) coupled to the instruction decoder (22) of the second microprocessor to receive the said information concerning the length of the operand and whether the access is read or write, and operative to store said information out of the instruction decoder temporarily and then feedback the stored information to the first microprocessor (10) in response to a control signal given by the first microprocessor. A control system as claimed in claim 6 wherein the feedback means further includes: A decoder (25) being coupled to the address decoder and operative to decode the select signal and output a control signals for controlling the second microprocessor (28) and the feedback means (21, 23). A control system as claimed in claim 6 wherein the control signals outputted from the decoder include: A starting signal to an operation execution unit (24) of the second microprocessor; a read control signal to the feedback port (23); and a write control signal to the command port (21). A control system as claimed in claim 1 wherein the first microprocessor is composed of a one-chip large scale integrated circuit in which the detecting means is incorporated. A control system as claimed in claim 1 wherein the second microprocessor is composed of a one-chip large scale integrated circuit in which the feedback means is incorporated.

Inventors: NAKAYAMA, TAKASHI C/O NEC CORPORATION
Applicants: NEC CORPORATION
Application year: 1986
Main classification: G06F9
IPC codes: G06F9, G06F15, G06F12