ARMLINK: Fill Unused Flash Content With Predefined Value

Information in this support solution applies to:

• Keil MDK

QUESTION

How do I fill up unused flash content with a specific value?

ANSWER

The following steps are required:

• Add the following linker switch to Project -> Options for target -> Linker -> Misc Controls:
  

  --pad=VALUE
  

  Where VALUE is an integer, which can be given in hexadecimal format. If value is greater than 0xFF, then the padding byte is set to (char)value.
• Create an dummy section in your scatter file with the used flash size:
  

  END_OF_BLOCK (FLASH_BASE + FLASH_SIZE) FIXED EMPTY 0x0 {}
  

  The scatter file can be found in your output directory with the output file name and the extension .sct e.g. Blinky.sct. To enable scatter file usage uncheck Project -> Options for target -> Linker -> Use Memory Layout from Target Dialog and specify the scatter file below in the same dialog.

  An example scatter file, demonstrating the solution, is the following:

  LR_IROM1 0x08000000 0x00010000  {    ; load region size_region
    ER_IROM1 0x08000000 0x00010000  {  ; load address = execution address
     *.o (RESET, +First)
     *(InRoot$$Sections)
     .ANY (+RO)
     .ANY (+XO)
    }
    RW_IRAM1 0x20000000 0x00020000  {  ; RW data
     .ANY (+RW +ZI)
    }
    END_OF_BLOCK (0x08010000) FIXED EMPTY 0x0 {}
  }
  

Please note, if you fill-up the full flash size with a specific value the output file size will be increased. Downloading to flash will take longer, depending on the amount of flash space.

MORE INFORMATION

• Refer to --pad=num in the Compiler Reference Guide.
• Refer to Arm Linker in the µVision User's Guide.
• Refer to Scatter File Syntax in the Compiler Reference Guide.

Last Reviewed: Monday, February 15, 2021