How to debug code on external flash?

[shabbir.hussain]

I'm trying to debug code in external flash memory mapped at 0x90000000. However, I get the following error when looking at the disassembly during debug.

 Failed to execute MI command:
          -data-disassemble -s 2415922564 -e 2415922663 -- 3
          Error message from debugger back end:
          Cannot access memory at address 0x90000d86

I first verified an led blinking program on the internal flash then compiled and linked it to external flash by changing the .LD script. I compiled a .bin file that I then turned into a header file using the command xxd -h blinky.bin > blinky.h.

/* Entry Point */
ENTRY(Reset_Handler)
 
/* Highest address of the user mode stack */
_estack = 0x20050000;    /* end of RAM */
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0x200;      /* required amount of heap  */
_Min_Stack_Size = 0x400; /* required amount of stack */
 
/* Specify the memory areas */
MEMORY
{
RAM (xrw)      : ORIGIN = 0x20000000, LENGTH = 320K
FLASH (rx)      : ORIGIN = 0x90000000, LENGTH = 8192K
}
 
/* Define output sections */
SECTIONS
{
  /* The startup code goes first into FLASH */
  .isr_vector :
  {
    . = ALIGN(4);
    KEEP(*(.isr_vector)) /* Startup code */
    . = ALIGN(4);
  } >FLASH
 
  /* The program code and other data goes into FLASH */
  .text :
  {
    . = ALIGN(4);
    *(.text)           /* .text sections (code) */
    *(.text*)          /* .text* sections (code) */
    *(.glue_7)         /* glue arm to thumb code */
    *(.glue_7t)        /* glue thumb to arm code */
    *(.eh_frame)
 
    KEEP (*(.init))
    KEEP (*(.fini))
 
    . = ALIGN(4);
    _etext = .;        /* define a global symbols at end of code */
  } >FLASH
 
  /* Constant data goes into FLASH */
  .rodata :
  {
    . = ALIGN(4);
    *(.rodata)         /* .rodata sections (constants, strings, etc.) */
    *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
    . = ALIGN(4);
  } >FLASH
 
  .ARM.extab   : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >FLASH
  .ARM : {
    __exidx_start = .;
    *(.ARM.exidx*)
    __exidx_end = .;
  } >FLASH
 
  .preinit_array     :
  {
    PROVIDE_HIDDEN (__preinit_array_start = .);
    KEEP (*(.preinit_array*))
    PROVIDE_HIDDEN (__preinit_array_end = .);
  } >FLASH
  .init_array :
  {
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(SORT(.init_array.*)))
    KEEP (*(.init_array*))
    PROVIDE_HIDDEN (__init_array_end = .);
  } >FLASH
  .fini_array :
  {
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP (*(SORT(.fini_array.*)))
    KEEP (*(.fini_array*))
    PROVIDE_HIDDEN (__fini_array_end = .);
  } >FLASH
 
  /* used by the startup to initialize data */
  _sidata = LOADADDR(.data);
 
  /* Initialized data sections goes into RAM, load LMA copy after code */
  .data : 
  {
    . = ALIGN(4);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
 
    . = ALIGN(4);
    _edata = .;        /* define a global symbol at data end */
  } >RAM AT> FLASH
 
  
  /* Uninitialized data section */
  . = ALIGN(4);
  .bss :
  {
    /* This is used by the startup in order to initialize the .bss secion */
    _sbss = .;         /* define a global symbol at bss start */
    __bss_start__ = _sbss;
    *(.bss)
    *(.bss*)
    *(COMMON)
 
    . = ALIGN(4);
    _ebss = .;         /* define a global symbol at bss end */
    __bss_end__ = _ebss;
  } >RAM
 
  /* User_heap_stack section, used to check that there is enough RAM left */
  ._user_heap_stack :
  {
    . = ALIGN(4);
    PROVIDE ( end = . );
    PROVIDE ( _end = . );
    . = . + _Min_Heap_Size;
    . = . + _Min_Stack_Size;
    . = ALIGN(4);
  } >RAM
 
  
 
  /* Remove information from the standard libraries */
  /DISCARD/ :
  {
    libc.a ( * )
    libm.a ( * )
    libgcc.a ( * )
  }
 
  .ARM.attributes 0 : { *(.ARM.attributes) }
}

In a separate project, I program an external qspi flash with the contents of the blinky program. I memory map the external flash and then jump to execute that code.

/* Jump to user application */
		  JumpAddress = *(__IO uint32_t*) (QSPI_FLASH_FIRST_PAGE_ADDRESS + 4); // Program Counter of user App is stored at this location
		  Jump_To_Application = (pFunction) JumpAddress;
		  /* Initialize user application's Stack Pointer */
		  __set_MSP(*(__IO uint32_t*) QSPI_FLASH_FIRST_PAGE_ADDRESS);
		  Jump_To_Application();
		  /* do nothing */
		  while(1);

I checked the variables and indeed the jump address corresponds to the build analyzer memory details of the reset handler. When the code jumps into the flash at address 0x90000e78 (reset handler), I can read the first few assembly instructions. But after a certain number instructions I see the error message above.

Why is the assembly not viewable during debug mode? Have I linked my program correctly to run on an external flash?

[AVI-crak]

First you need to assemble the firmware with the new QUADSPI section

QUADSPI (rx): ORIGIN = 0x90000000, LENGTH = 32M

Place the program code and static data in the QUADSPI section, under the name of the new function (it’s easier).

 .qspimram:

 {

  . = ALIGN (4);

  _sqspimram =.; / * create a global symbol at ccmram start * /

  * (. qspimram)

  * (. qspimram *)

  . = ALIGN (4);

  _eqspimram =.; / * create a global symbol at ccmram end * /

 }> QUADSPI

Extract the QUADSPI section from the created ***.elf file and save it to the ***.bin binary file. (periods and spaces are important !!!)

arm-none-eabi-objcopy -O binary -j .qspimram bin \ Release \ ***.elf bin \ Release \ ***.bin

Program external memory using any available methods - data from ***.bin.

Program the internal memory of MK with data from ***.elf.

to build a new firmware ***.elf without changing ***.bin - you can not !!!

Enjoy the pain of a new error found - repeat the algorithm until the perfect code.

[Tesla DeLorean]

Usually one needs a debugger script to get external memory working before you can look at it.

You'll need flashing code (loader) to deliver the code, and code within your own startup to bring it up.

Break-point after you've configured the pins, memory, and mapped it.

Validate the settings/connectivity thoroughly. I would suggest checksumming the entire span of the memory several times and make sure it really does run properly at 66 or 100 MHz, with the mapping/read commands you've picked.