MCUBoot using W25Q SPI Flash not working (use of Zephyr semaphore)

[Olivier-ProGlove]

spi_flash_w25qxxdv still uses Zephyr semaphore kernel while MCUBoot uses CONFIG_MULTITHREADING=n. As discussed in various Github issues #8368, #9808 problems might exist when using Zephyr kernel API with CONFIG_MULTITHREADING=n.

When W25Q SPI Flash initializes itself, it checks if the Flash ID matches the expected one. To do that it sends a command through SPI using spi_transceive().

All/Most SPI drivers use spi_context.h that uses Zephyr semaphore API.

Instructions to duplicate the issue on nRF52840 PCA10056 (but the issue could in theory be duplicated on any board that their SPI driver uses spi_context.h such as the following SPI drivers: DW, Intel, STM32, Nordic) and there is no need of W25Q SPI Flash as the crash occurs before any SPI transmission:

• Add to boot/zephyr/prj.conf

CONFIG_SPI=y
CONFIG_SPI_0=y
CONFIG_SPI_NRFX=y

CONFIG_FLASH=y
CONFIG_SPI_FLASH_W25QXXDV=y
CONFIG_SPI_FLASH_W25QXXDV_SPI_NAME="SPI_0"
CONFIG_SPI_FLASH_W25QXXDV_SPI_SLAVE=0

# Required by Zephyr v1.13 but must be removed for head of Zephyr (DTS is used instead):
CONFIG_SPI_0_NRF_SCK_PIN=13
CONFIG_SPI_0_NRF_MOSI_PIN=15
CONFIG_SPI_0_NRF_MISO_PIN=17
CONFIG_SPI_0_IRQ_PRI=3

It crashes with:

***** USAGE FAULT *****
  Illegal load of EXC_RETURN into PC
***** Hardware exception *****
Current thread ID = 0x00000000
Faulting instruction address = 0xf7ffeb04

I suspect it is due to the semaphore not being initialized but before investigating the issue myself I would like to know the decision for MCUBoot regarding CONFIG_MULTITHREADING=n.

[nashif]

You should be using multi-threading

[amcewen]

In case anyone else ends up here when trying to debug getting W25Q SPI flash working with Zephyr, adding CONFIG_MULTITHREADING=y in the MCUBOOT prj.conf (along with the CONFIG_SPI_NOR=y, CONFIG_SPI=y and CONFIG_PM_OVERRIDE_EXTERNAL_DRIVER_CHECK=y options) seems to do the trick.