How to diagnose a boot failure

1 Introduction

The blue and red LEDs on STM32 MPU boards are used to notify the user in case of boot failure during the boot chain execution and at runtime.

2 Description and debug

The statuses of blue and red LEDs allow to see at which stage the execution failed: the diagram below shows how each boot component uses these LEDs while the table gives more information on the way to interpret the LED statuses when the boot fails. Among the boot components, the FSBL can be TF-A or U-Boot SPL and the SSBL is U-Boot, as explained in the boot chain overview.

Blue LED	Red LED	System state	Action
Off	Blinking	The execution failed during ROM code execution	Check that: your microSD card is properly inserted in the board the boot pins configuration selects the boot device your boot memory was well programmed with STM32CubeProgrammer
On	Blinking	The execution failed during the second stage bootloader (SSBL)	See U-Boot - How to debug to investigate the failure
Off	Off	The execution may have failed: In FSBL execution After the SSBL execution but before the heartbeat (blue LED) started	See How to debug TF-A BL2 to investigate the failure See U-Boot - How to debug and how to trace and debug to investigate the failure
Off or on	Off	The execution may have failed during Linux® kernel execution between two heartbeat pulses (blue LED): a fatal error leading to a kernel panic might have occurred...	See Dmesg and Linux kernel log to investigate the failure
Blinking	Off	Your platform is alive	Enjoy !