How does the single-chip MCU make part of the code run in RAM? look here

MCU is different from the resource-rich Linux platform. MCU (such as Cortex M0+ based on Cortex V6M, etc.) Code usually runs in embedded Flash. In some specific applications, some functions need to be run in RAM. Yesterday, in order to solve this problem, a solution was implemented. The specific methods are as follows:

1. To implement the routine to run in RAM, this routine is implemented in pure assembly, such as:

__asm void program_word2addr(uint32_t addr, uint32_t data)


push {r3, r4, r5, lr} ;save some regsiters

/*your code for this routine*/

pop {r3, r4, r5, pc}


2. When compiling, use the compile option whose code has nothing to do with the running position, such as (Keil --apcs /ropi/rwpi), to generate *.axf;

3. Use fromelf -c to generate *.axf disassembly, find the corresponding program_word2addr implementation part, and copy the binary code corresponding to the routine to the code to be applied, in the form of a read-only array:


const staic uint16_t s_flashProg2AddressCode[16] = {...., ....}

4. Define a global array, such as static uint16_t g_code[16], size is exactly equal to the length of s_flashProg2AddressCode;

5. Define a function pointer, such as static void (*callFlashPrg2Address)(uint32_t addr, uint32_t data)

6. Define a function to run Code with RAM, such as:

void run_prgcode_onram(uint32_t addr, uint32_t data)


memcpy(g_code,s_flashProg2AddressCode,32 );

callFlashPrg2Address = (void (*)(uint32_t addr, uint32_t data))((uin32_t)g_code + 1);

callFlashPrg2Address (address, data);


run_prgcode_onram, you can run program_word2addr in RAM.

callFlashPrg2Address = (void (*)(uint32_t addr, uint32_t data))((uin32_t)g_code + 1); The purpose of +1, because the operating platform is Cortex V6M, the thumb instruction set used is completed according to the requirements of the ARM Spec.

callFlashPrg2Address (address, data); is the key to realize RAM running program_word2addr.

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