[OpenOCD-user] Flash programming on STM32L011 / L021 - with workaround

[Leonardo S. d. S. <leo...@gm...>]

Hello everyone,

I found a Flash programming issue on some parts and a workaround below.

OpenOCD loads this code in RAM to program any STM32Lx (loaded in
stm32lx_write_half_pages() ):

0x20000000  0x2300      MOVS    r3, #00
0x20000002  0xe004      B       0x2000000e
0x20000004  0xf851cb04  LDR     r12, [r1], #4   ; 0x04
0x20000008  0xf840cb04  STR     r12, [r0], #4   ; 0x04
0x2000000c  0x3301      ADDS    r3, #0x01
0x2000000e  0x4293      CMP     r3, r2
0x20000010  0xd3f8      BCC     0x20000004
0x20000012  0xbe00      BKPT    00


This code will always cause a Hard Fault on STM32L0 parts (undefined
instruction - this form of the LDR and STR instructions doesn't exist in
ARMv6-M). Usually, OpenOCD detects the Hard Fault and falls back to another
method.

The issue appears on STM32L011 and L021 that have the "empty check" and the
14-pin package. The factory bootloader (selected by default) takes over
from the Hard Fault handler. I think it reconfigures the SWD lines to
another function and the debug connection is lost.


*Workaround:*

I managed to program an STM32L021 after adding this to the config file:

$_TARGETNAME configure -event reset-end {
echo "Remapping Flash to address 0x00000000"
# RCC_APB2ENR <= 0x1
mww 0x40021034 0x1
# SYSCFG_CFGR1 <= 0x0
mww 0x40010000 0x0
}

It simply remaps the Flash to address 0 instead of bootloader ROM, changing
the Vector Table, so the Hard Fault handler from the bootloader never runs
and the connection is not dropped.


One more correction: config script target/stm32l0.cfg sets _WORKAREASIZE to
8 kB by default, but these new parts have only 2 kB RAM.

Regards,

Leonardo