AVR Freaks

To run a program compiled in ram needs to make some code to settle in flash. This code needs to identify if there is a program in sram and jump into sram code if there is one.

  uint32_t *pSrc, *pDest;

 if(*((uint32_t *) 0x20400004)==0x20400149){     //Check if there is program loaded in sram by matching start address

  __asm__ volatile(

  "MOV R0, PC \n\t"

  "LDR R1, =0X20400000 \n\t"                            // Same70 sram begin address

  "CMP R0, R1 \n\t"                                             // Compare current PC with sram begin address

  "BGT     label1 \n\t"                                           // IF current PC is greater than 0x20400000 means that program running in sram, no action required, jump out to label1

  "LDR r0, =0x20400000 \n\t"                              // Program is running in flash, loading stack pointer address

  "LDR SP, [R0] \n\t"                                            // Loading stack pointer

  "LDR  R0,=0x20400004 \n\t"                            // Loading sram program start address's address

  "LDR R0, [r0,#0] \n\t"                                       // Loading sram program start address

  "BX  R0 \n\t"                                                     // Go to sram Reset_handler code

  "label1: \n\t"

  :

  :

  :  "r0","r1"

  );

  }else{

   /* No sram program is loaded in sram area, initialize the relocate segment */

  pSrc = &_etext;

  pDest = &_srelocate;

  if (pSrc != pDest) {

   for (; pDest < &_erelocate;) {

    *pDest++ = *pSrc++;

   }

  }

 }

The following procedure works with SAM E70 Xplained Evaluation Board and Atmel Studio 7.0.1417. And only apply to atmel cortex M7 with 2M flash memory and 384K sram.

1. Open Atmel Studio Example project “Common IOPORT Service Example1-SAME70-XPLD”

2. Replace Reset_Handler() content with reset_handler.txt Reset_Handler content.

3. Replace linker script “flash.ld” content with run_in_flash.txt content.

4. Go to Tool screen, choose option Erase entire chip and boot from ROM to run the program. (Do not select Override Vector Table Offset Register)

5. Close this project.

6. Switch to the project that you want to run in sram.

7. Replace Reset_Handler content with reset_handler.txt Reset_Handler content.

8. Replace linker script “flash.ld” content with run_in_sram.txt content

9. Go to Tool screen, choose option Incremental programming and boot from ROM to run the program. (Do not select Override Vector Table Offset Register)

10. The program with start from flash and jump into sram program.

Note:

• Step 9 is critical. If you choose Erase entire chip at step 8, the program will end up anywhere, and you might need to erase the chip by jumper on the Xplained board and need to go to menu Tools --- Device Programming to set boot option bit to boot from flash.

• Step 4 and 9 was supposed to select boot from Flash. There might be some unknown issue in Atmel Studio 7.0.1417.  Old version was ok to select boot from Flash or Unchanged.