By PURPLELEC | 25 October 2023 | 0 Comments
What are arm embedded memories?
It is usually the highest-speed memory in embedded development. It is composed of edge-triggered flip-flops and gate circuits, and is extremely expensive. Its main function is to temporarily store numbers or instructions.
A flip-flop can store 1-bit binary code, so a register that stores n-bit binary codes needs to be composed of n flip-flops.
2. Cache Cache
Cache can be understood as a memory that connects the upper and lower parts. It transfers data to the CPU and obtains data from the main memory.
In order to alleviate the speed difference between the CPU and main memory, the introduction of Cache, an intermediate medium that is slower than the CPU but faster than the main memory, will effectively solve the contradiction caused by the speed difference. Furthermore, storage is localized. When the CPU is running, the accessed data will tend to be in a smaller local space address.
Therefore, the cache Cache is used to store the currently most active programs and data and interact directly with the CPU.
RAM is the abbreviation of random access memory. Its stored content can be taken out or stored at will, and the access speed has nothing to do with the location of the storage unit. The storage speed is fast. It is usually used as temporary data storage for the operating system or other running programs. medium.
This kind of embedded memory will lose its storage content when the power is cut off, so it is used to store programs and data that are used for a short period of time. Common RAMs used in embedded development include: SRAM, DRAM, and DDRAM (double rate random access memory).
4. Main memory
There are two common types of main memory: ROM and Flash, which are generally used to store large amounts of data. People nowadays are accustomed to calling Flash ROM. In fact, ROM refers to read-only memory and there is a certain difference between Flash (flash memory). But Flash is developed from ROM and RAM. Flash is not only electronically erasable and programmable, but also can read data quickly, so it is often classified as ROM by e-commerce companies.
5. External memory
Common external memories are divided into disk storage, optical disk storage, CF card, and SD card. Generally used to save large amounts of data, its characteristics are as follows:
① Disk storage: It is divided into hard disk and floppy disk. It has large capacity and long service life but is expensive. It is mainly used in personal PCs and rarely appears in the embedded field.
② Optical disc memory: a disc that reads/writes information optically. It is generally used as a carrier of multimedia digital information and rarely appears in the embedded field.
③ CF card: The earliest memory card launched. It is smaller than magnetic disk storage and optical disk storage, has good antimagnetic properties and stable storage performance.
④ SD card: It can be regarded as an upgraded version of CF card. It is smaller than CF card and has higher security. It supports SD mode and SPI mode, and can be used for embedded development with only simple peripheral circuits. It is the most common external memory in the embedded field.
6. Storage management and page replacement algorithm
Through the above, I believe everyone should have a certain understanding of the embedded storage system. Then under this system, a problem will arise - when the memory required for the process to run is greater than the system memory, the entire process cannot be transferred into the system memory together. , so it cannot run. In order to solve the above contradiction, Weigu uses page storage or segment storage to divide the process space.
At this time, the total process space will become multiple small segments of process space, and then eliminated through the page replacement algorithm, so that the separated small segments of process space can be transferred into the memory in order to run.
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