How to use the BootLoader and APP program of STM32F4

1. Concept Literacy

1.IAP

IAP is the abbreviation of In Application Programming. IAP means that the user's own program burns part of the User Flash area during operation. The purpose is to easily update the firmware program in the product through the reserved communication port after the product is released .

Usually when users need to implement the IAP function, that is, to update the user program itself during operation, they need to write two project codes when designing the firmware program. The first project program does not perform normal functional operations, but only receives programs or data through some communication channels (such as USB, USART ) to execute updates to the second part of the code; the second project code is the real functional code.

2.Bootloader

In the above IAP concept, bootloader is the first project program. The main functions of bootloader are: receiving data from serial port, USB and other media; storing and moving data; program jump and other functions.

3. App

A name for the second project code in the IAP concept

Notes on writing bootloader and App for Stm32

1. How to allocate the address space of bootloader and app

2. How to get the upgrade software data and write it into flash

3. How to jump from bootloader to app

4. How to set the interrupt vector of App

5. How to generate bin file in App

6. Program execution process

1. How to allocate the address space of bootloader and app

Figure 1 STM32 Flash partitioning

(1) Assigning addresses

I am using STM32F407, its Flash size is 512K, so I divide it as follows:

0x08000000 --- 0x08010000 is allocated to the bootloader, the size is 64k

0x08010000----0x0801F000 is allocated to the first APP, and the size is 124k

0x0801FC00----0x0801FFFF is allocated to user_flag and other flags

(2) Set the ROM size in Keil

A. Setting the ROM size in BootLoader

B. Set the ROM size in the App

2. How to get the upgrade software data and write it into flash

In my program, I receive data through the serial port, and then call iap_write_appbin(u32 appxaddr,u8 *appbuf,u32 appsize) to store the received APP program in the FLASH of STM32F4, where appxaddr is the starting address of the application, appbuf is the application code, and appsize is the application size (bytes). The code is as follows:

#define FLASH_APP1_ADDR 0x08010000 //The first application start address

if(applenth) //Serial port receives data length

{

printf("Start updating firmware...\r\n");

LCD_ShowString(30,210,200,16,16,"Copying APP2FLASH...");

  if(((*(vu32*)(0X20001000+4))&0xFF000000)==0x08000000)//Judge whether it is 0X08XXXXXX.

{  

iap_write_appbin(FLASH_APP1_ADDR,USART_RX_BUF,applenth); //Update FLASH code   

LCD_ShowString(30,210,200,16,16,"Copy APP Successed!!");

printf("Firmware update completed!\r\n");

}else 

{

LCD_ShowString(30,210,200,16,16,"Illegal FLASH APP!  ");   

printf("Non-FLASH application!\r\n");

}

  }else 

{

printf("No firmware can be updated!\r\n");

LCD_ShowString(30,210,200,16,16,"No APP!");

}

clearflag=7; //The flag updates the display and clears the display after 7*300ms

void iap_write_appbin(u32 appxaddr,u8 *appbuf,u32 appsize)

{

u32 t;

u16 i=0;

u32 temp;

u32 fwaddr=appxaddr; //Currently written address

u8 *dfu=appbuf;

for(t=0;t

{   

temp=(u32)dfu[3]<<24;   

temp|=(u32)dfu[2]<<16;    

temp|=(u32)dfu[1]<<8;

temp|=(u32)dfu[0];  

dfu+=4; //Offset 4 bytes

iapbuf[i++]=temp;    

if(i==512)

{

i=0; 

STMFLASH_Write(fwaddr,iapbuf,512);

fwaddr+=2048; //Offset 2048 512*4=2048

}

} 

if(i)STMFLASH_Write(fwaddr,iapbuf,i);//Write the last few bytes of content.  

}

3. How to jump from bootloader to app

// Jump to the application segment

//appxaddr: user code starting address.

void iap_load_app(u32 appxaddr)

{

if(((*(vu32*)appxaddr)&0x2FFE0000)==0x20000000) //Check if the top address of the stack is legal.

{ 

jump2app=(iapfun)*(vu32*)(appxaddr+4); //The second word in the user code area is the program start address (reset address)

MSR_MSP(*(vu32*)appxaddr); //Initialize APP stack pointer (the first word in the user code area is used to store the top address of the stack)

jump2app(); //Jump to APP.

}

}

4. How to set the interrupt vector of App

SCB->VTOR = FLASH_BASE | 0x10000;/*The interrupt vector table is located at FLASH_BASE (0X08000000) + 0x10000*/

  Because the starting address of APP is (0X08000000)+0x10000

5. How to generate bin file in App

We click the Options for TargetUser tab in MDK, check Run #1 in the After Build/Rebuild column, and write: D:\tools\mdk5.14\ARM\ARMCC\bin\fromelf.exe --bin -o ..\OBJ\RTC.bin..\OBJ\RTC.axf, as shown in the figure:

6. Program execution process

Summarize:

The main contents of Bootloader are

1. Set the space for bootloader and app

2. Receive the compiled app bin file and write it to flash

3. Implement jump

The main changes in the App are

1. ROM starting address and allocated space size

2. Redirect interrupt vector

3. Generate bin file