JPH05120002A - Return address stack control circuit - Google Patents

Abstract

PURPOSE:To renounce an unnecessary stack without giving a burden on a micro program. CONSTITUTION:A pointer value which a stack pointer 17 holds is stored in a stack pointer storage part 12 at the time of executing a special sub-routine call instruction. At the time of executing a special return instruction, the pointer value which the stack pointer storage part 12 stores is written into the stack pointer 17, and the value of the return address of a sub-routine, which a stack memory 15 stores, is written into a program counter 16. Thus, some levels in the stacks of the return addresses of the micro program can be renounced with one instruction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a return address stack control circuit for managing a stack of a microprocessor, and more particularly to a return address stack control circuit devised to discard unnecessary stacks.

[0002]

2. Description of the Related Art Conventionally, for stack management of a microprocessor, there is a system in which a dedicated storage means for stack is used and the management is performed by hardware, and a microprocessor is accessible without such a dedicated storage means. There was a method in which an area for stacking was set on the memory and the microprogram managed this.

In the stack management method using hardware, the stack pointer as a register indicating the top of the stack memory cannot be controlled from the microprogram, and only the top of the stack memory is always controlled. Was said.

[0004]

In the microprocessor in which stack management is performed by hardware as described above, only the top of the stack memory is subject to control. For this reason, when attempting to discard several stacks and return to the original routine at once, a process for discarding the stack by the microprogram was required. As a result, there are problems that the processing efficiency of the microprogram is lowered and that if the processing is erroneous, the subsequent operation cannot be guaranteed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a return address stack control circuit that can discard unnecessary stacks without burdening the microprogram.

[0006]

According to a first aspect of the present invention, a stack memory prepared as dedicated storage means and a position storage means for storing a position where a return address of a microprogram is stored in the stack memory. Further, the return address stack control circuit is provided with a stack head quasi-means for simulating the position stored by the position storage means as the head of the stack memory that can be controlled by the microprogram.

That is, according to the first aspect of the present invention, the above-mentioned object is achieved by simulating the position of the stack stored by the position storage means as the top of the stack and processing.

According to the second aspect of the present invention, a stack memory prepared as a dedicated storage means, a position storage means for storing a position where a return address is stored in the stack memory when a special subroutine call instruction is executed,
The return address stack control circuit is provided with return processing means for simulating the position of the stack memory stored by the position storage means as the top of the stack when the return instruction from the special subroutine is executed.

That is, according to the second aspect of the invention, the position of the stack in which the return address is stored at the time of executing the special subroutine call instruction is stored in the position storing means, and this position is stored at the time of executing the return instruction from the special subroutine. By assuming that it is the top of the stack and processing the return,
The above-mentioned object is achieved.

According to the third aspect of the present invention, the stack memory prepared as a dedicated storage means and the position of the stack memory where the return address stored by this position storage means at the time of execution of the special subroutine call instruction are stored. Position storing means for storing, return processing means for simulating the position of the stack stored by the position storing means as the head of the stack memory when the return instruction from the special subroutine is executed, and return processing, and a special stack control instruction Storage control means for storing the position of the stack memory in the position storage means during execution of, and stack memory head moving means for moving the head of the stack memory to this stored position when executing another special stack control instruction. It is provided in the return address stack control circuit.

That is, according to the third aspect of the invention, the position of the stack in which the return address is stored at the time of executing the special subroutine call instruction is stored in the position storage means, and this position is stored at the time of executing the return instruction from the special subroutine. While simulating the top of the stack and performing return processing, the position of the stack is stored in the position storage means when a special stack control instruction is executed, and the top of the stack is moved to this stored position. By doing so, the above-mentioned object is achieved.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows a configuration of a return address stack control circuit according to an embodiment of the present invention. This circuit includes an instruction decoding unit 11 that decodes microinstructions. The type of the instruction decoded by the instruction decoding unit 11 is the stack pointer storage unit 1
2, the stack pointer controller 13, the stack memory 15 and the program counter 16, respectively. The stack pointer control unit 13
By this instruction, the stack pointer 17 is controlled to be incremented or decremented, and the stack pointer value stored in the stack pointer storage unit 12 is controlled to be written. Stack pointer 17
Holds the pointer of the stack memory 15, updates the pointer according to the instruction of the stack pointer control unit 13, and instructs the stack memory 15 of the pointer. The stack memory 15 is a dedicated memory for storing the contents of the program counter 16 last in, first out. The program counter 16 is a counter that holds the execution address of the microprogram.

First, the case where normal stack control is performed will be described.

When a normal subroutine call instruction is executed, the instruction decoding unit 11 that has decoded the instruction instructs the stack memory 15 that the instruction is a subroutine call instruction. Upon receipt of the instruction, the stack memory 15 stores the contents of the program counter 16 which is the return address of the subroutine. Next, the instruction decoding unit 11 instructs the stack pointer control unit 13 and the program counter 16 that it is a subroutine call instruction. The program counter 16 sets the address of the subroutine based on this. Stack pointer control unit 13
Updates the stack pointer 17 and ends the execution of the subroutine call instruction.

When a normal return instruction is executed, the instruction decoding unit 11 which has decoded the instruction instructs the stack pointer control unit 13 that the instruction is a return instruction. The stack pointer control unit 13 updates the stack pointer 17. Next, the instruction decoding unit 11 uses the program counter 16
Is instructed to be a return instruction, and the return address value of the subroutine stored in the stack memory 15 pointed to by the stack pointer 17 is written in the program counter 16. Thus, the execution of the return instruction is completed.

Next, a case where special stack control is performed will be described.

First, when a special subroutine call instruction is executed, the instruction decoding unit 11 instructs the stack pointer storage unit 12 that it is a special subroutine call instruction. The stack pointer storage unit 12 that has received the instruction stores the pointer value held by the stack pointer 17.
In other respects, the same operation as the normal subroutine call instruction is performed, and the execution of the subroutine call instruction is completed.

Next, when a special return instruction is executed, the instruction decoding unit 11 instructs the stack pointer control unit 13 that it is a special return instruction. Upon receiving the instruction, the stack pointer control unit 13 writes the pointer value stored in the stack pointer storage unit 12 into the stack pointer 17. Next, the instruction decoding unit 11 uses the program counter 1
6 is instructed to be the return instruction, the value of the return address of the subroutine stored in the stack memory 15 pointed to by the stack pointer 17 is written in the program counter 16, and the execution of the special return instruction is completed.

When the stack pointer storage instruction is executed, the stack pointer storage unit 12 stores the stack pointer 1
The pointer value held by 7 is stored, and the execution of the instruction ends.

When the stack pointer return instruction command is executed, the stack pointer control unit 13 writes the pointer value stored in the stack pointer storage unit 12 into the stack pointer 17, and the execution of the command ends.

[0022]

As described above, according to the present invention, by storing the position of the stack for storing the return address of the microprogram and processing this stack position as the top of the stack, unnecessary stacks are once Therefore, it is possible to prevent the deterioration of the processing efficiency of the microprogram. Further, since special processing for discarding the stack by the microprogram is not required, there is an effect that it is possible to prevent a malfunction due to a mistake in this processing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a return address stack control circuit according to an embodiment of the present invention.

[Description of Reference Signs] 11 instruction decoding unit 12 stack pointer storage unit 13 stack pointer control unit 15 stack memory 16 program counter 17 stack pointer

Claims (3)

[Claims] 1. A stack memory prepared as a dedicated storage means, a position storage means for storing a position where a return address of a microprogram is stored in the stack memory, and a position stored by the position storage means. A return address stack control circuit, comprising: a stack head control means for controlling a head of the stack memory capable of controlling a microprogram. 2. A stack memory prepared as a dedicated storage means, a position storage means for storing a position where a return address is stored in this stack memory when a special subroutine call instruction is executed, and a return instruction from a special subroutine. A return address stack control circuit comprising: return processing means for simulating the position of the stack memory stored by the position storage means at the time of execution as the top of the stack and performing return processing. 3. A stack memory prepared as a dedicated storage means, and a position storage means for storing the position of the stack memory in which the return address stored by this position storage means is stored when a special subroutine call instruction is executed. , When the return instruction from a special subroutine is executed, the position of the stack stored by this position storage means is assumed to be the top of the stack memory, and the return processing means performs return processing, and when the special stack control instruction is executed, the stack memory A storage control means for storing the position in the position storage means; and a stack memory head moving means for moving the head of the stack memory to the stored position when executing another special stack control instruction. Return address stack control circuit.