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reading STM32L15x program counter (with HAL defines?)

Question asked by Lynn Linse on Dec 12, 2016
Latest reply on Dec 12, 2016 by Clive One

Question - What is the safest way to 'peek' at the STML152 program counter? Ideally something in the standard HAL files (so no ASM; I am working under AC6 in C). I wish my code to understand if it was loaded/is running in the lower 1 of 2 flash banks (? PC < 0x8004000), or in the upper 2 of 2 banks (PC > 0x8004000).


Background - this is a kind of dual boot issue, but not really. The L152 has 512K flash in 2 x 256K banks and we plan to load 2 similar images in the two 256K banks. We'll always boot from the lower bank image, but wish to load field fw upgrades into the upper bank image, understanding that the reflash might fail & need to be erased completely. The upper bank will be re-written by our own code (FW read from a special secure SPI token), and that loading code will be linked to load/run from the upper bank only.


The goal is to treat the lower bank as a "factory default image", and the upper bank as a "field written & perhaps broken image". So we want a simple piece of code that basically does this IF test:

if(I am running in lower bank - aka: PC < X?)

  then I am factory image

      if(secure token is in place)

          consider reflash of upper FW - means one needs to power-cycle with secure token in place to reflash


         examine upper image for validity (crc, maybe digital hash signature)

         if(upper image is valid)

             then jump to it & run

             else erase the invalid image & continue running the original factory image.

  else I am field image (PC > X?), so just run & don't bother looking for second/upper image or token


So the goal is to load new fw from the secure token, while running in the lower/factory image. I can completely erase the upper bank and attempt to write. We assume if the write is aborted, we'd end up with a partial/invalid image and the above test-for-validity could detect the bad FW status & erase it. We plan to use flash protection to disable the normal STLink reflash for field units (so one would need to erase all flash to re-enable such fw loading).