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stm32: Fix printing value of pyb.CAN auto_restart on FDCAN hardware. - #18951

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projectgus:bugfix/pyb_can_print_auto_restart
Mar 19, 2026
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stm32: Fix printing value of pyb.CAN auto_restart on FDCAN hardware.#18951
dpgeorge merged 1 commit into
micropython:masterfrom
projectgus:bugfix/pyb_can_print_auto_restart

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@projectgus

@projectgus projectgus commented Mar 19, 2026 •
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Summary

As pointed out in #18572 (comment). The DAR register field is for disabling auto-retransmit, FDCAN hardware doesn't support automatic restart to clear Bus Off.

This work was funded through GitHub Sponsors.

Testing

Manually built a NUCLEO_G474RE board and ran the pyb_can.py unit test.

Generative AI

I did not use generative AI tools when creating this PR.

@projectgus

projectgus commented Mar 19, 2026

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Very glad this doesn't change the print output, so don't have to revisit the pyb_can.py test! (DAR is always un-set, so it prints False before and after this fix.)

@projectgus projectgus mentioned this pull request Mar 19, 2026
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projectgus
projectgus commented Mar 19, 2026
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Comment thread ports/stm32/pyb_can.c
@@ -144,7 +144,7 @@ static void pyb_can_print(const mp_print_t *print, mp_obj_t self_in, mp_print_ki
self->can_id,
mode,
#if MICROPY_HW_ENABLE_FDCAN
(self->can.Instance->CCCR & FDCAN_CCCR_DAR) ? MP_QSTR_True : MP_QSTR_False
MP_QSTR_False // auto_restart not supported on FDCAN hardware
#else
(self->can.Instance->MCR & CAN_MCR_ABOM) ? MP_QSTR_True : MP_QSTR_False

@projectgus projectgus Mar 19, 2026

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Uncrustify insists on this indent here, for whatever reason. 🤷

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github-actions Bot commented Mar 19, 2026 •
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Code size report:

Reference:  stm32: Add machine.CAN implementation. [6cac2d2]
Comparison: stm32: Fix printing value of pyb.CAN auto_restart on FDCAN hardware. [merge of c802a13]
  mpy-cross:    +0 +0.000% 
   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
      esp32:    +0 +0.000% ESP32_GENERIC
     mimxrt:    +0 +0.000% TEENSY40
        rp2:    +0 +0.000% RPI_PICO_W
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:    +0 +0.000% VIRT_RV32

dpgeorge
dpgeorge approved these changes Mar 19, 2026
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Thank you!

@dpgeorge

dpgeorge commented Mar 19, 2026

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Very glad this doesn't change the print output, so don't have to revisit the pyb_can.py test! (DAR is always un-set, so it prints False before and after this fix.)

Yes, I saw this as well in my testing.

@dpgeorge dpgeorge added this to the release-1.28.0 milestone Mar 19, 2026
@projectgus @dpgeorge
stm32: Fix printing value of pyb.CAN auto_restart on FDCAN hardware.
c802a13 
The DAR register field is for auto-retransmit, FDCAN doesn't support
automatic restart to clear Bus Off.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <[email protected]>
@dpgeorge
dpgeorge force-pushed the bugfix/pyb_can_print_auto_restart branch from 716e3f0 to c802a13 Compare March 19, 2026 14:18
@dpgeorge
dpgeorge merged commit c802a13 into micropython:master Mar 19, 2026
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@projectgus
projectgus deleted the bugfix/pyb_can_print_auto_restart branch March 20, 2026 01:11
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