CN1828557A - Realization Method of Process Mapping in Embedded Operating System - Google Patents

Abstract

As the importance of process management in embedded OS, this invention realizes conversion from user address to physical address by virtual address mapping, and divides the virtual address into the kernel state and user state for right address conversion and saving space. This invention has important meaning to embed OS.

Description

Realization Method of Process Mapping in Embedded Operating System

technical field

The invention relates to a real-time task processing technology, in particular to a method for realizing process mapping in an embedded operating system.

Background technique

Memory management is an important part of the operating system, which is responsible for managing the memory of the computer system. Memory can be divided into two categories: main memory (referred to as main memory) and auxiliary memory (referred to as auxiliary memory).

The storage space of the main memory is generally divided into two parts: one part is the system area, which stores the operating system and some standard subroutines, routine programs, etc.; the other part is the user area, which stores user programs and data. Storage management is mainly to manage the user area in the main memory.

After the computer system adopts multi-programming technology, it often needs to store programs of multiple processes in the main memory at the same time, and the locations of these programs in the main memory cannot be known in advance, so users cannot use absolute addresses when writing programs. The address indicated by the address part in the instructions of a modern computer is usually an address, and logical addresses can be numbered starting from 0. Users write programs in terms of logical addresses. When loading a program into a computer, first, the operating system must allocate a suitable main memory space for it. Since the logical address is often inconsistent with the absolute address of the allocated main memory space, and the processor executes instructions according to the absolute address, it is necessary to convert the logical address into an absolute address to obtain the real storage place of the information. The work of converting a logical address into an absolute address is called address translation.

When multiple processes share the main memory, the programs and data in the main memory must be protected and allocated reasonably and effectively so as to fully utilize the efficiency of the main memory.

In order to make it easier for the user to program, so that the user is not limited by the actual capacity of the main memory when writing the program, a certain technology can be used to "expand" the main memory capacity, and a main memory space larger than the actual capacity can be used.

Contents of the invention

The purpose of the present invention is to provide a method for realizing process mapping in an embedded operating system.

The technical scheme that the present invention solves its technical problem adopts is as follows:

Provide two virtual memories for each process, one is the virtual memory in the core state, using the group of active page registers in this state to realize the mapping of its virtual and physical addresses; the other is the virtual memory in the user state, using the The set of active page registers in the state is used to realize the mapping of its virtual and physical addresses. The maximum virtual memory in these two states is 64K bytes.

1) Virtual space address

With the support of the storage management component, the 16-bit byte address is no longer directly interpreted as a physical address, but is regarded as a virtual space address;

Divide the 64K-byte virtual space address space into 8 pages, each page is divided into 128 blocks, and each block is 64 bytes, so each page can reach up to 8K bytes. In order to make full use of the memory space, the system is based on virtual pages. The page length is used to allocate memory space;

2) Active page register

The actual location of the virtual memory page in the memory needs to be reflected by a mapping table. This mapping table is composed of two sets of active page registers, one for the core state and one for the user state. Each group has 8 32-bit long registers, each of which is divided into two: one is the page address register, and the other is the page description register;

The page address register is used to record the starting block number of each page corresponding to the virtual space address space in the memory;

The page specification register records the access authority, extension direction, and length of each page corresponding to the address space of the virtual space. The 1st and 2nd bits of the register indicate the access rights to the corresponding page, the 3rd bit indicates the expansion direction of the page, and the 8th to 14th bits of the register are the actual length of the virtual page, expressed by how many blocks it contains;

3) virtual - physical address conversion

After obtaining the address of the virtual memory space, the conversion from the virtual space address to the physical address is realized according to the following process:

The first step is to determine the current operating state of the processor according to the 14th and 15th bits of the processor status word, thereby selecting the corresponding active page register group;

The second step is to obtain the corresponding page address register home page description register in the group from the page number in the virtual space address;

The third step is to form the physical block number in the memory from the "starting block number of this page in the memory" in the page address register and the "block number in the page" in the virtual space address, and check the block number by the page description register legality;

In the fourth step, the physical address corresponding to the virtual space address is formed from the physical block number and the "displacement amount" in the virtual space address.

4) The virtual space address space of the process in the core state

In the core state, the process runs the operating system program. To use the core stack area, the user structure of the process is used. The composition of the virtual space address space in this state includes:

In user mode, the process involves sharing the text segment, data area, and user stack area when running

5) The actual distribution of the process image in memory

① Install pages 0 to 5 of the core state virtual space address space at the low address starting from address 0 of the memory, and reside in the memory;

② Install the 7th page input and output page of the core state virtual space address space in the 8K space at the highest address of the memory, and reside in the memory;

③According to the current storage allocation situation, put the shared text segment in a continuous area in units of memory blocks;

④According to the current storage allocation, put the 1024-byte content in the core state virtual space address space, the data area in the user state virtual space address space, and the user stack area in a continuous area in units of memory blocks to form the data segment of the process image;

⑤ Send the starting block number of the shared text segment of the process whose process image is all in the memory to the corresponding shared text segment of the memory for storage.

The beneficial effects of the present invention are: the present invention adopts the method of virtual address mapping to realize the conversion from user address to physical address, divides the virtual address into kernel state and user state, and divides the protection level, which not only ensures the correct address of each process Converting and extracting the shared data of each process saves storage space, providing the greatest convenience, safety and efficiency for both the memory management of the operating system and the writing and running of user programs.

Description of drawings

Figure 1 virtual space address;

Fig. 2 processor status word;

Figure 3 page address register;

Figure 4 also illustrates the registers;

Figure 5 virtual physical address translation;

Figure 6 The actual distribution of the process image in memory.

Detailed ways

When implementing real-time task scheduling, it is written in C language, and the specific method is as follows:

Provide two virtual memories for each process, one is the virtual memory in the core state, using the group of active page registers in this state to realize the mapping of its virtual and physical addresses; the other is the virtual memory in the user state, using the The set of active page registers in the state is used to realize the mapping of its virtual and physical addresses. The maximum virtual memory in these two states is 64K bytes.

1) Virtual space address

With the support of the storage management component, the 16-bit byte address is no longer directly interpreted as a physical address, but is regarded as a virtual space address, as shown in Figure 1:

Divide the 64K-byte virtual space address space into 8 pages, each page is divided into 128 blocks, and each block is 64 bytes, so each page can reach up to 8K bytes. In order to make full use of the memory space, the system is based on virtual pages. The page length is used to allocate memory space.

2) Active page register

The actual location of the virtual memory page in the memory needs to be reflected by a mapping table. This mapping table is composed of two sets of active page registers, one for the core state and one for the user state. Each group has 8 32-bit long registers, each of which is divided into two: one is the page address register, as shown in Figure 3, and the other is the page description register, as shown in Figure 4:

The page address register is used to record the starting block number of each page corresponding to the virtual space address space in the memory. Divide the memory into blocks in units of 64 bytes, a total of 4096=2 ¹² blocks, numbered 0~(2 ¹² -1), and memory allocation is in units of blocks. Each page address register only uses its lower 12 bits to record the starting block number of each page corresponding to the virtual space address space in the memory.

The page specification register records the access authority, extension direction, and length of each page corresponding to the address space of the virtual space. The 1st and 2nd bits of the register indicate the access rights to the corresponding page, the 3rd bit indicates the expansion direction of the page, and the 8th to 14th bits of the register are the actual length of the virtual page, expressed by how many blocks it contains.

3) virtual - physical address conversion

After obtaining the address of the virtual memory space, the conversion from the virtual space address to the physical address is realized according to the following process, as shown in Figure 5:

The first step, according to the 14th, 15th bits of the processor state word (as shown in Figure 2), determine the running state that processor is in now, select corresponding active page register group thus;

The second step is to obtain the corresponding page address register home page description register in the group from the page number in the virtual space address;

The third step is to form the physical block number in the memory from the "starting block number of this page in the memory" in the page address register and the "block number in the page" in the virtual space address, and check the block number by the page description register legality;

In the fourth step, the physical address corresponding to the virtual space address is formed from the physical block number and the "displacement amount" in the virtual space address.

4) The virtual space address space of the process in the core state

In the core state, the process runs the operating system program, and the core stack area needs to be used to use the user structure of the process. Among them, pages 0-5 store the operating system code, which includes the process structure of the resident memory; Page 7 stores content related to system input and output, called input and output pages; page 6 contains part of the code area of the running process, namely the user structure and core stack, which actually only use 1024 bytes. For all processes, the contents of pages 0-5 and page 7 are the same.

In user mode, the shared text segment, data area, and user stack area are involved when the process is running:

The arrangement principle of virtual space address space in this state is as follows:

① Arrange from low to high to share the text segment first, and then to the data area; place the stack area from high to low;

② Use pages as the allocation unit, and if there is less than one page, it will be aligned page by page. As shown in Figure 14(a), if the length of the shared text segment is 2.5 pages, it will occupy 0-2 pages in the virtual space address space; if the data area is 2.25 pages, then the shared text segment in the virtual space address space will occupy 3 to 5 pages; the stack area is 0.5 pages, which occupies the seventh page of the virtual space address space and extends to the lower address direction. At this time, page 6 of the virtual space is blank and unoccupied.

5) The actual distribution of the process image in memory

Although each process has a core-state virtual space address space, the contents of pages 0-5 and page 7 are exactly the same. In addition, even the user-mode virtual space of each process cannot be copied into the memory intact according to its allocation, otherwise it will cause a huge waste of memory space. Therefore, the real distribution of each process image in memory is shown in Figure 6:

① Install pages 0 to 5 of the core state virtual space address space at the low address starting from address 0 of the memory, and reside in the memory;

② Install the 7th page input and output page of the core state virtual space address space in the 8K space at the highest address of the memory, and reside in the memory;

③According to the current storage allocation situation, put the shared text segment in a continuous area in units of memory blocks;

④According to the current storage allocation, put the 1024-byte content in the core state virtual space address space, the data area in the user state virtual space address space, and the user stack area in a continuous area in units of memory blocks to form the data segment of the process image;

⑤ Send the starting block number of the shared text segment of the process whose process image is all in the memory to the corresponding shared text segment of the memory for storage.

Claims (1)

1. a process mapping implementation method in an embedded operating system, characterized in that: Provide two virtual memories for each process, one is the virtual memory in the core state, using the group of active page registers in this state to realize the mapping of its virtual and physical addresses; the other is the virtual memory in the user state, using the The group of active page registers in the state is used to realize the mapping of its virtual and physical addresses. The virtual memory in these two states is at most 64K bytes; 1) virtual space address With the support of the storage management component, the 16-bit byte address is no longer directly interpreted as a physical address, but is regarded as a virtual space address; Divide the 64K-byte virtual space address space into 8 pages, each page is divided into 128 blocks, and each block is 64 bytes, so each page can reach up to 8K bytes. In order to make full use of the memory space, the system is based on virtual pages. The page length is used to allocate memory space; 2) Active page register The actual location of the virtual memory page in the memory needs to be reflected by a mapping table. This mapping table is composed of two sets of active page registers, one for the core state and one for the user state, each group has 8 32-bit long registers, each divided into two: one is the page address register, and the other is the page description register; The page address register is used to record the starting block number of each page corresponding to the virtual space address space in the memory; The page description register records the access rights, extension direction, and length of the page corresponding to the virtual space address space. The first and second bits of the register indicate the access rights to the corresponding page, and the third bit indicates the extension of the page. Direction, the 8th to 14th bits of the register are the actual length of the virtual page, expressed by how many blocks it contains; 3) virtual - physical address conversion After obtaining the address of the virtual memory space, the conversion from the virtual space address to the physical address is realized according to the following process: The first step is to determine the current operating state of the processor according to the 14th and 15th bits of the processor status word, thereby selecting the corresponding active page register group; The second step is to obtain the corresponding page address register page description register in the group from the page number in the virtual space address; The third step is to form the physical block number in the memory from the "starting block number of this page in the memory" in the page address register and the "block number in the page" in the virtual space address, and check the block number by the page description register legality; The fourth step is to form the physical address corresponding to the virtual space address from the physical block number and the "displacement amount" in the virtual space address; 4) The virtual space address space of the process in the core state; In the core state, the process runs the operating system program. To use the core stack area, the user structure of the process is used. The composition of the virtual space address space in this state includes: In user mode, the process involves sharing the text segment, data area, and user stack area when running; 5) The actual distribution of the process image in memory ① Install pages 0 to 5 of the address space of the virtual space in the core state at the low address starting from address 0 of the memory, and reside in the memory; ② Install the 7th page input and output page of the core state virtual space address space in the 8K space at the highest address of the memory, and reside in the memory; ③According to the current storage allocation situation, put the shared text segment in a continuous area in units of memory blocks; ④According to the current storage allocation, put the 1024-byte content in the core state virtual space address space, the data area in the user state virtual space address space, and the user stack area in a continuous area in units of memory blocks to form the data segment of the process image; ⑤ Send the starting block number of the shared text segment of the process whose process image is all in the memory into the corresponding shared text segment of the memory for storage.

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