GPREGRET register causing data corruption when set during custom use-case

RE: GPREGRET register causing data corruption when set during custom use-case

rbmarcus — Fri, 17 May 2024 19:09:19 GMT

Thank you for confirming that the GPREGRET register should not affect flash on reboot with my custom bootloader. I tested again today and analyzed the binary blob at each step of the process, and it is indeed unrelated to GPREGRET. I hadn't been giving enough time for the fstorage init and store calls to process, so I would get occasional corruption. I tested the 4 trials mentioned in my first post a handful more times, and the error rate between them is completely random. After gating fstorage calls behind a flag set by the callback handler, I am now able to safely transfer the blob without error.

I'm concerned about this current transfer method, so I will be exploring alternative options for OTA DFU. Thank you again for the information you provided.

RE: GPREGRET register causing data corruption when set during custom use-case

Vidar Berg — Tue, 14 May 2024 11:27:57 GMT

Hello,

The GPREGRET registers are meant to be retained through soft resets, as shown in the table here: Reset behavior. We also use these registers in our SDK examples to enable the application to signal the bootloader to enter DFU mode following a soft reset.

[quote user=""]What does setting GPREGRET trigger after a reboot, aside from holding the values that were set?[/quote]

These are just general-purpose retention registers and will not have any effect unless the application or bootloader is actually using them. The SoftDevice/MBR does not use them.

[quote user=""]How can I prevent the flash region where my binary blob is stored from being modified, unless done so directly in custom code via the bootloader main[/quote]

I'm not sure what could be corrupting the data. What kind of corruption are you seeing? Is there any pattern, or does it seem arbitrary? You can use nrfjprog to inspect the memory.

$ nrfjprog --memrd 0x70000 --n 0x70000 > dfu_slot.txt

[quote user=""]Are there any other registers I can use to pass a flag to the bootloader without triggering any SDK functionality?[/quote]

I'm not sure what SDK functionality it could be since you are using a custom bootloader. If there is, you should be able to find references to it by searching through your bootloader and application project for 'gpregret'.

Best regards,

Vidar

RE: GPREGRET register causing data corruption when set during custom use-case

hmolesworth — Tue, 14 May 2024 02:50:29 GMT

So .. I tested this, albeit on an nRF52833 'cos I couldn't be bothered to switch to an nRF52840. Data sheet indicates identical performance, soft reset retains registers .. after 100 soft resets (no errata, power on, no debugger attached):

Results: mResetCount = 100, SRAM_OkCount = 100, GPREGRET_OkCount = 100, GPREGRET2_OkCount = 100

// Place following data in section .noinit so it doesn't get wiped on a reset
#pragma default_variable_attributes = @ ".noinit"
  // Valid data indication for this data
  static volatile uint32_t mIamInitialized    __attribute__((section(".noinit")));
  static volatile uint32_t mDummyGPREGRET     __attribute__((section(".noinit")));
  static volatile uint32_t GPREGRET_OkCount   __attribute__((section(".noinit")));
  static volatile uint32_t GPREGRET2_OkCount  __attribute__((section(".noinit")));
  static volatile uint32_t SRAM_OkCount       __attribute__((section(".noinit")));
  static volatile uint32_t mResetCount        __attribute__((section(".noinit")));
#pragma default_variable_attributes =
// End - Place following data in section .noinit so it doesn't get wiped on a reset

#define MAGIC_8BIT_CODE1  96
#define MAGIC_8BIT_CODE2  23
#define MAGIC_8BIT_CODE3 102
  void TestGPREGRET(void)
  {
     char InfoPacket[120] = "";
     mResetCount++;
     if (mDummyGPREGRET == MAGIC_8BIT_CODE1)
     {
        SRAM_OkCount++;
     }
     if (NRF_POWER->GPREGRET == MAGIC_8BIT_CODE2)
     {
        GPREGRET_OkCount++;
     }
     if (NRF_POWER->GPREGRET2 == MAGIC_8BIT_CODE3)
     {
        GPREGRET2_OkCount++;
     }
     // See if data is valid - Use unique device ID as the valid signature
     if (mIamInitialized != NRF_FICR->DEVICEID[0])
     {
        // Indicated data is now valid - Use unique device ID as the valid signature
        mIamInitialized = NRF_FICR->DEVICEID[0];
        mResetCount       = 0;
        SRAM_OkCount      = 0;
        GPREGRET_OkCount  = 0;
        GPREGRET2_OkCount = 0;
        mDummyGPREGRET       = MAGIC_8BIT_CODE1;
        NRF_POWER->GPREGRET  = MAGIC_8BIT_CODE2;
        NRF_POWER->GPREGRET2 = MAGIC_8BIT_CODE3;
     }
     if (mResetCount < 100)
     {
        // Trigger another reset
        NVIC_SystemReset();
     }
     // break after all the reset tests, log results
     // Results: mResetCount = 100, SRAM_OkCount = 100, GPREGRET_OkCount = 100, GPREGRET2_OkCount = 100
     snprintf(InfoPacket, sizeof(InfoPacket)-1, "Results: mResetCount = %u, SRAM_OkCount = %u, GPREGRET_OkCount = %u, GPREGRET2_OkCount = %u\r\n", mResetCount, SRAM_OkCount, GPREGRET_OkCount, GPREGRET2_OkCount);
     uartSend(InfoPacket, strlen(InfoPacket));
     while(1) ;
  }