JP2001147822A - Real time monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a real time monitor for using general registers to be used for a plurality of uses by limiting one part of the general registers to be used by a mult-task in a CPU having general registers such as RISC even when register saving and restoring processing increasing in proportion to the number of the general registers results in one factor of the increase of the overhead of a real time monitor. SOLUTION: In this real time monitor, the number of general registers to be used can be limited by using general resisters whose use is clear for other uses, or temporarily saving the general registers in stacks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a real-time monitor in a microprocessor embedded device which is a multitask system.

[0002]

2. Description of the Related Art A general real-time monitor saves and restores all general-purpose registers of a CPU in register save / restore processing that occurs each time a task is switched. In the CPU, the number of general-purpose registers is large, which contributes to the overhead of the real-time monitor.

The operation of the conventional real-time monitor configured as described above will be described. One of the functions of the real-time monitor is task control. Execution control of a plurality of tasks is performed while switching tasks. When a task is switched while a task is running, it is necessary to maintain the state of the task in preparation for the task to be restarted. Among the information to be held, there is a save of a register. Also, the next task to be executed is executed after restoring the previously saved register before the task is restarted.

In this process of saving and restoring registers, a general real-time monitor performs saving and restoring for all registers. However, if the number of registers is large, such as a RISC CPU, the real-time monitor is not used in the system.
Increases the time, or overhead, to use, and consequently reduces system performance.

[0005] For example, the SH-
In 1 (7032/7034), 15 general-purpose registers from R0 to R14 are prepared. Moreover, the registers R0 to R7 have clear uses. Therefore,
The number of general-purpose registers to be used can be limited by using these eight registers together for another purpose or by temporarily saving them on the stack.

Incidentally, the general-purpose register 15 is used as usual.
If all the books are saved and restored, 1 per register
Assuming that it takes μ second, it takes 15 μ second. Therefore, if the number of registers used in the task is limited to eight, it takes only 8 μs. For example, assuming that task switching occurs in all tasks with the number of tasks being 60, register return 6
0 times and register save 60 times are required. If there are 15 general-purpose registers to be saved and restored, 15 μs * (60+
60) = 1800 μsec = 1.8 msec. If there are eight registers to save, 8 μs * (60 + 6
0) = 960 μs. That is, if the number of registers to be saved is reduced by half, the processing time is also reduced by half. As the number of tasks increases, the effect of reducing the time for register save / restore processing is obtained.

The SH-1 uses a general-purpose register when performing interrupt prohibition processing. Therefore, if the interrupt prohibition process is performed before the register is saved in the task switching, there is a problem that the contents of the general-purpose registers used in the interrupt prohibition process are destroyed. Therefore, in order to prevent the contents of the register from being destroyed, it is necessary to save the contents before the interrupt prohibition processing. By limiting the number of general-purpose registers to be saved and restored, another effect is to disable interrupts.
If the interrupt prohibition permission process is performed by using a register that is not saved / restored at the time of the permission process, it is not necessary to save before interrupt prohibition.

When performing the interrupt prohibition process, it is necessary to hold the contents of the status register before the prohibition. Declare it as a local variable. However, since the general-purpose register is used in the interrupt prohibition processing as described above, it is necessary to save beforehand before the interrupt prohibition processing. For this reason, since the stack is saved on the stack in the middle of saving, extra control of the stack pointer is required. If a general-purpose register not used for this is applied, the same effect as in claim 2 can be obtained.

[0009]

In a general real-time monitor, all general-purpose registers of the CPU are saved and restored in a register saving and restoring process that occurs each time a task is switched. However, especially in a CPU such as RISC, the number of general-purpose registers is large,
There has been a problem that the length of the processing time for register restoration / save is a factor in the overhead of the real-time monitor.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. The present invention limits the number of general-purpose registers owned by a CPU used in a task, reduces overhead of a real-time monitor, and improves system performance. It is an object of the present invention to provide a real-time monitor.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a multitasking system in which, when a CPU having a plurality of general purpose registers is used, a general purpose register used in a task is used for a plurality of purposes. Some general-purpose registers have been restricted and used.

According to the present invention, a CPU used in a task
The configuration is such that the number of owned general-purpose registers is limited, the overhead of the real-time monitor is reduced, and a real-time monitor capable of improving the performance of the system can be realized.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention described in claim 1 of the present invention is a general-purpose system which uses a general-purpose register used for a task for a plurality of purposes when a CPU having a plurality of general-purpose registers is used in a multitask system. Registers are restricted and used, and general-purpose registers that are not used by tasks are used by the real-time monitor itself by reusing general-purpose registers for which a specific use has been determined or saving them to the stack. Can be used for other purposes.

According to a second aspect of the present invention, in the first aspect, a general-purpose register not used in the task is used for interrupt disabling processing. In the return processing, it is possible to prevent the contents of the general-purpose registers from being destroyed due to the interrupt inhibition processing.

According to a third aspect of the present invention, in the first aspect of the present invention, a general-purpose register not used in a task is used for temporarily saving a status register before interrupt disable processing. The control of the stack pointer can be omitted in the return / evacuation processing of.

Hereinafter, embodiments of the present invention will be described. FIG. 1 is a diagram showing a clear application example of a general-purpose register included in a CPU according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a register save / restore process between a general-purpose register and a stack of the CPU, and FIG. 3 is a flowchart of the register save / restore process. FIG. 4 is a diagram illustrating the use of general-purpose registers in the interrupt prohibition process, and FIG. 5 is a diagram illustrating saving of an interrupt mask (status register) in the interrupt prohibition process.

First, an example of preconditions for explaining the contents of the present invention is assumed. For the sake of convenience, the number of general-purpose registers owned by the CPU is assumed to be 16 from R0 to R15 in order to distinguish registers. Also, R0 to R7 are used as registers for tasks, and R8 to R1 are used as registers.
5 is a register used in the real-time monitor. R0 to R
7, R15. An example of usage definition of each register is shown below. R0 is a register for holding the return value of the function, R1 to R3 are registers for holding the temporary value, and R4 to R7.
Is a register for holding a function argument, and R15 is a stack pointer. R0 is a register for holding the return value of the function, but since it is sufficient to finally hold the return value,
Before that, it can be used for other purposes. The registers holding the arguments of R4 to R7 can be used for another purpose by immediately processing them or saving them to a temporary stack or the like. The registers holding the temporary values of R1 to R3 can be similarly used for other purposes. Therefore, R0
To R7 can be used for multiple purposes.

In FIG. 1, R0 to R7 (1 to 8)
And R15 (16) have clear uses, and R15 (16)
0 (1) stores the return value from the function,
R1 to R3 (2 to 4) are used to temporarily hold values when performing calculations and the like, and R4 to R7 (5
To 8) store the arguments when the function is called, and R15 (16) stores the stack pointer.

Generally, R8 to R14 (9 to 1)
General-purpose registers up to 5) are also used for some purposes. The number of registers to be used can be limited by substituting a general purpose register for which a clear purpose is determined for the purpose. For example, FIG.
Indicates the usage status of the general-purpose register at the time of function call. If there is an argument, R4 to R7 shaded with dots
In (5 to 8), the argument at the time the function is called is stored, so if it is used for another purpose as it is, the value will be destroyed and normal operation cannot be guaranteed. Therefore, if the value of the register is processed or saved in another unused general-purpose register or stack in advance, it can be used for another purpose.

FIG. 3B shows the usage status of the general-purpose register during function processing. R1 to R3 shaded with diagonal lines
(2 to 4) are used to temporarily hold values during calculation and the like. As in the case of (A), if the value of the register is processed or saved in another unused general-purpose register or stack in advance, it can be used for another purpose.

FIG. 2C shows the use state of the general-purpose register immediately before the function returns. R0 (1) shaded by a vertical line
Stores the return value from the function. Since the return value may be stored immediately before the end of the function, it can be used for another purpose until then. This allows
It is possible to speed up the process of saving and restoring registers necessary for task switching, and to simplify the process by using general-purpose registers whose use is restricted for other purposes of the real-time monitor. .

Generally, in a system that performs multitask processing, there are a plurality of tasks, and each processing is performed.
Each process is being advanced, and tasks are switched for that purpose. Each time the task is switched, the register is saved and restored. The left side of FIG. 2 shows a case of general register saving / restoring, which is a conventional method, in which 15 general registers R0 to R14 (17 to 31) are saved in a stack (32). The right side shows an example of register save / restore in the present invention, in which eight general registers R0 to R7 (33 to 40) are saved in a stack (41). The number of general-purpose registers to be saved and restored is about half on the right side according to the present invention, and the saving and restoring processing time can be obviously reduced by almost half.

Next, regarding the register save / restore processing,
explain. As described above, a multitask system has a plurality of tasks, and while switching tasks,
Processing to be performed for each task is in progress. When switching tasks, it is necessary to maintain the state immediately before switching so that the task can be restarted. This is done by saving the register. In addition, it is necessary to return the held state to the CPU in preparation for the task to be started next. That is done by restoring the register.

Next, the flow of the register save / restore process will be described. Since register save and register return are almost the same processing, the register save processing will be described. Normal processing is to perform interrupt prohibition processing before performing register saving processing. However, general-purpose registers may be used in interrupt prohibition processing.
In this case, unless the general-purpose registers used in the interrupt prohibiting process are saved, the general-purpose registers used are destroyed.

Here, the register save processing will be described with reference to FIG. First, the task relinquishes CPU usage,
Control passes to the monitor (42). The general-purpose registers used in the interrupt prohibition processing are saved (43). Next, the status register immediately before interrupt prohibition is saved (44). Then, an interrupt prohibition process is performed (45). Then, the remaining general-purpose registers are saved (46).

Then, the status register saved in (44) is restored (47), and finally, interrupt permission processing is performed (4).
8), the register save processing ends. Then, a task to be started next is searched, and when the task is searched, register return processing is performed in preparation for starting the task (49). Finally, the right to use the CPU is passed from the monitor to the next task, and the next task is started (50).

FIG. 4 shows an example in which another use in the above description "by using another use of the real-time monitor" is used for interrupt prohibition processing. First, the interrupt prohibition processing will be described. The interrupt prohibition process is a process necessary to prevent the destruction of the register value due to the interrupt by prohibiting the interrupt before the save / restore process of the register at the time of task switching. In this example, it is assumed that general-purpose registers R0 to R3 are used for the interrupt prohibition processing. But,
If this interrupt prohibition processing is performed before saving the register, the general-purpose registers R0 to R3 are used, and the value of the register is destroyed before saving. Therefore, the general-purpose registers used in the interrupt processing are substituted for R0 to R3, and the use is restricted to R8 to R11 (55 to 58).
, The value of the register can be prevented from being destroyed. This is another effect of limiting the general-purpose registers to be used.

FIG. 5 shows an example in which another use in the above description "by using the real-time monitor for another use" is used to hold an interrupt mask in interrupt prohibition processing. First, the holding of the interrupt mask in the interrupt prohibition process will be described. The interrupt disabling process is performed by masking the interrupt priority bit of the status register. Therefore, it is necessary to hold the state before being masked by some method and to return in the interrupt permission processing. Therefore, the status register immediately before the interrupt prohibition process is saved to R9 (64) which restricts the use, so that the value of the register can be prevented from being destroyed. This is another effect of limiting the general-purpose registers to be used.

[0029]

As described above, according to the present invention, the overhead of the real-time monitor can be reduced and the system performance can be improved by reducing the register save / restore processing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a clear example of use of general-purpose registers of a CPU according to an embodiment of the present invention;

FIG. 2 is an explanatory diagram of register save / restore processing between a general-purpose register and a stack of a CPU according to an embodiment of the present invention;

FIG. 3 shows a register save / restore operation in one embodiment of the present invention.
Flowchart of return processing

FIG. 4 is an explanatory diagram of a usage state of general-purpose registers in interrupt prohibition processing according to the embodiment of the present invention;

FIG. 5 is an explanatory diagram showing how an interrupt mask (status register) is stored in an interrupt prohibiting process according to the embodiment of the present invention;

[Explanation of symbols]

 1, 17, 33, 66 General-purpose register (R0) 2, 18, 34, 67 General-purpose register (R1) 3, 19, 35, 68 General-purpose register (R2) 4, 20, 36, 69 General-purpose register (R3) 5, 21, 37, 51, 60 General purpose register (R4) 6, 22, 38, 52, 61 General purpose register (R5) 7, 23, 39, 53, 62 General purpose register (R6) 8, 24, 40, 54, 63 General purpose Register (R7) 9, 25, 55 General-purpose register (R8) 10, 26, 56, 64 General-purpose register (R9) 11, 27, 57 General-purpose register (R10) 12, 28, 58 General-purpose register (R11) 13, 29 General-purpose Register (R12) 14,30 General-purpose register (R13) 15,31 General-purpose register (R14) 16 General-purpose register (R15)

Claims (3)

[Claims] In a multi-task system, when a CPU having a plurality of general-purpose registers is used, the general-purpose registers used in the task are used for a plurality of purposes, and the general-purpose registers are partially used. monitor. 2. The real-time monitor according to claim 1, wherein a general-purpose register not used in the task is used for interrupt disabling processing. 3. The real-time monitor according to claim 1, wherein a general-purpose register not used in the task is used for temporarily saving the status register before the interrupt disable processing.