Write bootloader from 0

So-called bootloader Boot loader , Be similar to windows Inside BIOS, It is used for loading some environments and necessary initialization before the program runs .
And the single chip microcomputer bootloader Mainly for OTA Upgraded , The function is to initialize the necessary running environment , Determine whether to upgrade , If you want to upgrade , Then copy the downloaded upgrade program to the operation of the MCU flash in , Then jump to APP Program running address , If you don't upgrade, jump directly to APP Program running address .

bootloader Implementation function diagram

Is to achieve a jump .

Realization bootloaer And running the program requires two documents ：
1.bootloader Program engineering

1. Set up bootloader Program start position of , Such as 1 Shown , Generally not changed .
2. Set up bootloader The size of the program , As shown in Figure 2 , Generally, it is more practical to use bootloaer The program needs a little more space .
2.APP Program settings

Same as bootloader The same meaning , however APP The running address needs to be set by you cheaply bootloader The address size of , stay 2 You also need to reduce your settings bootlader Program size of

You can also change the starting position of the program here , But it is not recommended to change here , Just use the default here .

notes ：SP The stack pointer does not need to be changed , Because bootloader and APP Only one program is running at the same time , So only one program is using the stack .

APP Program
1. No exception vector table is required

You don't need the exception vector table to jump to APP The program start address can be executed .

2. Need exception vector table

When the program jumps , If you directly use the address as a pointer , Pay attention to ,Thumb Instruction sets and ARM The difference between instruction sets .

typedef void(*IapAppFun)(void); 	// Define a function pointer , Used to jump to APP Program 
#define 	FLASH_APP_ADDR  0x08010000		// Definition APP Program start address 
void main
{
	IapAppFun JumpApp;
	//	bootloader Some column initialization to be done 
	if (((*(__IO uint32_t *)FLASH_APP_ADDR) & 0xFF000000) == 0x08000000) 
	{
		__disable_irq();// Turn off interrupt 
		JumpApp = (IapAppFun)*(__IO uint32_t *)(FLASH_APP_ADDR +4);
		SCB->VTOR = FLASH_BASE|0x10000; // Inside the chip FLASH The starting address plus the offset address will be equal to APP The starting address of the program 
		JumpApp();
	}
	printf("APP is invalid!\r\n");// If the execution reaches here, it means that the jump fails 
}

if (((*(__IO uint32_t )FLASH_APP_ADDR) & 0xFF000000) == 0x08000000)
The purpose of this sentence is to judge FLASH_APP_ADDR The value stored in this address is used to jump to flash OK operation SRAM Or other places , If M3 As an example , So if it is SRAM The operation should be changed to
if ((((__IO uint32_t *)FLASH_APP_ADDR) & 0x2FF80000) == 0x20000000) From SRAM Began to run

This depends on where the upgrade program you write wants to start .

JumpApp = (IapAppFun)*(__IO uint32_t *)(FLASH_APP_ADDR +4);
The purpose of this sentence is because ,FLASH_APP_ADDR The address of the exception vector table is stored on , Add 4 The following address means that the program start address is stored inside , So we need to use dereference plus its value to get it and give it to the function pointer , Used to jump execution APP Program .

SCB->VTOR = FLASH_BASE|0x10000;
The purpose of this sentence is to change APP Program exception vector table , because APP The program is relative to 0x08000000 Has shifted 0x10000, So the first address after the offset stores the exception vector table .

The above is purely personal opinion , I hope you can correct the mistakes .