JPS6141422B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microprogram control device in a data processing device.

Reading, interpreting, and executing instructions in a data processing device can all be accomplished by combining dozens of basic operations, such as transferring information between registers, starting main memory, shifting digits, and using adders. is performed by sequentially executing several to several dozen commands.

In general, commands that specify the basic operations mentioned above are called microinstructions, and programs that are one level lower than normal programs that are made up of a set of microinstructions are called microprograms.

The microprogram control method used in data processing devices uses microprograms instead of the conventional combination of flip-flops and gates, which simplifies control and also simplifies the controlled logic. It has the advantage of easy design and the ability to easily expand and change functions by rewriting the storage device that stores the microprogram.

By taking full advantage of this advantage, it is possible to code program routines at the microprogram level. Programs coded using microprograms can give detailed operation instructions to the hardware, so compared to program routines assembled using only instructions, functions such as parallel operation can be added, and as a result, the performance of the hardware can be fully improved. This enables faster processing than when coding with software instructions. However, the number of steps in a microprogram realized by such a method will not increase dramatically compared to the number of steps in a microprogram that simply replaces the conventional control method using flip-flops and gates to add the above-mentioned functions. Inevitable. Implementing a control memory to store all the steps of this microprogram will increase the cost and expand the implementation space. For this reason, microprograms are divided into frequently used routines and less frequently used routines, a resident area and an overlay area are provided in the control memory, and frequently used microprogram routines stored in the normally resident area can be stored in the same manner as before. A microprogram overlay control method (hereinafter referred to as "overlay") is adopted in which when a microprogram routine that is executed and infrequently used is required, the necessary microprogram steps are loaded from external storage into the overlay area of the control memory.

This overlay control method includes two methods described below. Firstly, all overlay control is carried out under microprogram control, with no involvement of software programs at all.Secondly, overlay instructions, including overlay address specification, are performed using software instructions, and the hardware is executed according to these instructions. In this method, software control and microprogram control are performed, and the overlay operation is thereby executed. Due to its nature, such overlay instructions are performed only by the system program, not by the user program. Even if such a system program is adopted, it is difficult to eliminate program errors, and overlay addressing errors may occur if infrequently used microinstructions are superimposed on a system program consisting of frequently used microinstructions in the resident area. If you do, there is a high possibility that the system will become unpredictable and unrecoverable. To avoid this situation, it is necessary to protect the resident area of the control memory from being rewritten.

As a conventional protection method for resident areas, it is common to adopt the protection method used for main memory. For example, a method that uses a base address register that holds the start address of the overlay area, an address register, and an address adder circuit to specify the address of the overlay area using a relative address, or an overlay method that uses an address conversion buffer that converts a logical address to a physical address. There is a method for managing areas.

However, these schemes have the disadvantage of requiring extensive hardware, resulting in increased cost, and increased overhead for managing the overlay area and control memory address generation time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microprogram control device that can protect a resident area of a control memory during an overlay operation with less hardware.

The device of the present invention includes: a rewritable microinstruction storage means for storing a plurality of microinstructions; a microinstruction address storage means for storing address information indicating a storage location of the microinstruction storage means; micro-instruction storage means for storing a write instruction micro-instruction for instructing writing of the micro-instruction storage means; write address storage means for storing a write address to the micro-instruction storage means; and an address of the micro-instruction address storage means and the write address storage means. and means for controlling a write operation of the microinstruction storage means according to the comparison result of the comparison means when a write instruction microinstruction is given from the microinstruction storage means. It is characterized by:

Next, the present invention will be explained in detail using the drawings. One embodiment of the present invention shown in FIG. 1 includes a control memory 1 storing a microprogram;
microinstruction registers 2 and 3, microinstruction address register 4, which hold microinstructions having operation instruction parts and branch address parts read from microinstruction registers 2 and 3, microinstruction address register 4; deciphers the output of the switching circuit 5 which selects the control memory 1 as the address to be accessed, the +1 adder 6 which generates the output value +1 of the switching circuit 5, and the microinstruction register 2 which holds the operation instruction section of the microinstruction; Decoder 7 that generates a control signal, Decoder 7
The arithmetic circuit 8 is controlled by the output control signal of the arithmetic circuit 8, and the control circuit 1 holds the value sent from the arithmetic circuit 8.
1, microinstruction address register 4
Write address register 9, microinstruction address register 4 and write address register 9 to be transferred to
a comparison circuit 10 that compares the magnitude of the values held by the decoder 7, a control circuit 11 that refers to the control signal instruction from the decoder 7 and the output of the comparison circuit 10, and manages the write operation of the control memory 1; It consists of an external memory 12 that stores programs and a data register 13 that holds data retrieved from the external memory 12. In addition, in the figure, the arithmetic circuit 8, external memory 12, and control circuit 1
1, and other control lines are omitted.

Next, the operation of this embodiment will be explained in detail.

The address held in microinstruction address register 4 accesses control memory 1 via switching circuit 5, and the microinstruction read from control memory 1 is set in microinstruction registers 2 and 3. The outputs of microinstruction registers 2 and 3 are decoded by decoder 7 and instruct the operation of arithmetic circuit 8 in the form of control signals. On the other hand, the output of the switching circuit 5 is incremented by "1" by the +1 addition circuit 6, and is set in the microinstruction address register 4 as the address to be executed next. By repeating this operation, microprograms assigned to consecutive addresses are sequentially executed. When the microinstruction instructs a branch of the microprogram, the value of the microinstruction register 3 is selected by the switching circuit 5, the control memory 1 is accessed, and the branch is made to the address indicated by the microinstruction register 3. Control memory 1 is added by adding 1 to the address or branching.
The processing is continued in the arithmetic circuit 8 by appropriately extracting microinstructions from the microinstructions and executing the operations instructed by the microinstructions.

In the course of continuing processing, if an event occurs that requires a microprogram routine that is not stored in control memory 1, the microprogram branches to the microprogram overlay management routine (this routine resides in control memory). . This management routine determines the required microprogram routine and sends a data request from the microinstruction register 2 to the external memory 12 via the decoder 7. Data retrieved from external memory 12 is set in data register 13. Also, in this management routine, the arithmetic circuit 8
, generates a control memory address for storing the microprogram retrieved from the external memory 12, sets it in the write address register 9, and supplies a write instruction signal for the control memory 1 to the control circuit 11 via the decoder 7. do. The write address value of the control memory 1 set in the write address register 9 is compared by the comparison circuit 10 with the read address of the control memory 1 that stored the microinstruction that generated the write instruction signal. Comparison circuit 10
If the output of indicates that the write address is larger than the read address, the control circuit 11 transfers the contents of the write address to the microinstruction address register 4, and then transfers the microprogram set in the data register to the control memory 1. , writes to the address specified by the microinstruction address register 4. On the other hand, if the output of the comparison circuit 10 indicates that the write address is smaller than the read address, the control circuit 11 blocks the transfer to the microinstruction address register 4 and does not perform the write operation to the control memory 1.

As described above, the control memory write control mechanism of the microprogram control device of this embodiment prevents a write operation to an address smaller than the address at which the microinstruction that generates the write instruction signal of the control memory 1 is stored. Therefore, a write operation to the resident area can be prevented by placing a microinstruction that generates a control memory write instruction at an appropriate position in the resident area (for example, at the maximum address of the resident area).

FIG. 2 is a circuit diagram of a part of the control circuit 11, and according to the comparison result generated on the comparator output signal line 20, a write pulse sent on the write timing signal line 24 is applied to the control memory by an AND gate 21. By controlling the propagation to the write signal line 22 and setting it in the flip-flop 23, the output signal line 25 of the flip-flop 23 can be referenced by the microprogram. By adopting the configuration of the present invention, the microprogram can easily recognize the occurrence of an overlay addressing failure.

The present invention has the advantage that the protection function of the resident area of the control memory can be realized with a small amount of hardware and without increasing the overhead for realizing the protection function.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing the control circuit 11 shown in FIG. 1 and 2, 1...control memory, 2 and 3...microinstruction register, 4...
...Microinstruction address register, 5...Switching circuit, 6...+1 adder, 7...Decoder, 8...
Arithmetic circuit, 9...Write address register, 10
... Comparator, 11 ... Control circuit, 12 ... External memory, 13 ... Data register, 20 ... Comparator output signal line, 21 ... AND gate, 22 ... Control memory write signal line, 23 ... Flip flop.

Claims (1)

[Scope of Claims] 1. Rewritable microinstruction storage means for storing a plurality of microinstructions; microinstruction address storage means for storing address information indicating a storage location within the microinstruction storage means; and the microinstruction storage means. microinstruction storage means for storing a write instruction microinstruction for instructing writing to the microinstruction storage means; write address storage means for storing a write address to the microinstruction storage means; and an address stored in the microinstruction address storage means. and an address stored in the write address storage means; and a comparison means for comparing the address stored in the write address storage means; A microprogram control device comprising: means for controlling a write operation of the means.