Segger Fixed Memory Allocation in Flash and SoftDevice compatibility.

[snoopy20]

Hi All,

New user here but couldn't find a concrete answer to the following question.

In PIC land I've usually allocated fixed memory using the _at_ or __attribute__ label but Segger doesn't support this. From googling I read to add a reference to the xml file, which I've done as shown below:

<!DOCTYPE Board_Memory_Definition_File>
<root name="nRF52810_xxAA">
  <MemorySegment access="ReadOnly" name="FLASH1" size="0x00030000" start="0x00000000" />
  <MemorySegment access="Read/Write" name="RAM1" size="0x00006000" start="0x20000000" />
  <MemorySegment access="Read/Write" name="CODE_RAM1" size="0x00006000" start="0x00800000" />

  <MemorySegment name="$(FLASH_NAME:FLASH)">
    <ProgramSection alignment="4" load="Yes" name=".settingsStore" start="0x00000000" />
  </MemorySegment>
</root>

You can see that the start is 0x0 which is probably a bad idea, likely the entry point of the application if it's like PIC's. A related question to ask at this point is where does a SoftDevice get placed in Flash?

Back to the main question, I then have the following to take up a 4kb page of flash (actual usage is 1kb so plenty for futureproofing).

static const union {
  struct settingsProto settings;
  uint8_t pad[FLASH_PAGE_SIZE_BYTES];
} store __attribute__((section(".settingsStore"))); // reserve flash page

Upon build I receive the error:

unplaced section: .settingsStore [config.o], size=4000, align=4

[snoopy20]

Regarding APP_CODE_BASE and APP_RAM_BASE, the doc says "sd_softdevice_enable" returns the address, which is confusing because I need to compile the main application with those addresses prior to execution. Anyhow, I expected something similar to the xml flash reservation to tell the compiler to reserve the APP_CODE_BASE/APP_RAM_BASE space?

[bjorn-spockeli]

sd_softdevice_enable will return the APP_RAM_BASE. The APP_RAM_BASE is adjusted by modifying the RAM_START value under Code > Linker > Section Placement Macros. 

[snoopy20]

So to get this value I have to compile a little code, add the softdevice and execute then see what it returns, but the code won't have the correct offsets so won't run. Seems to be catch 22.

[bjorn-spockeli]

The sd_softdevice_enable call should return regardless of which RAM_START address that is used by the application. You can set the RAM_START address to the minimum RAM requirement stated in the SoftDevice release notes of the SoftDevice you are using.