Slow boot_validate / crc32_compute

[Bwalker]

I'm using the NRF52832 BLE DFU bootloader to run my code (slightly modified from the secure DFU example). At the start of my application, I toggle a pin and measure this with an oscilloscope. With a valid application and normal bootloader, there is a delay of around 450ms between power applied and the pin being toggled. If I return true before the CRC compute in boot_validate in app_is_valid (nrf_bootloader.c and nrf_dfu_validation.c), the startup time goes to around 10ms. Is it expected that it would take this long to check the CRC of the application? Are there any suggestions on ways to improve this, or skip it under certain conditions?

[Jørgen Holmefjord]

Hi,

The CRC check will depend on the length of the application firmware. If your application is large, the time sounds plausible. Using a more efficient crypto library may reduce the time a bit, but I'm not sure how much you can gain for such a simple calculation.

I did some comparison of Hash-checking with nRF Oberon and ARM Cryptocell CC310 backend in the bootloader in nRF52840, and it seems that the HW solution is about 5 times faster than SW libraries. Unfortunately, nRF52832 does not contain the cryptocell HW.

It is possible to disable the CRC check for situations where the chip is reset by a wake from System OFF, or when GPREGRET2 register is set, using the config NRF_BL_APP_CRC_CHECK_SKIPPED_ON_GPREGRET2 and NRF_BL_APP_CRC_CHECK_SKIPPED_ON_SYSTEMOFF_RESET

Best regards,
Jørgen