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SoC: stm32c0 support#3174

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petejohanson merged 3 commits intozmkfirmware:mainfrom
petejohanson:soc/stm32c0-support
Jan 7, 2026
Merged

SoC: stm32c0 support#3174
petejohanson merged 3 commits intozmkfirmware:mainfrom
petejohanson:soc/stm32c0-support

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@petejohanson petejohanson commented Dec 28, 2025

Small changes needed to support stm32c0

  • Add a new nBOOT_SEL bit initialization check, to ensure the BOOT pin works properly after flashing ZMK the first time.
  • Pull in fork of hal_stm32 that has one small USB fix cherry picked in. Will not be needed once we move to a newer Zephyr version.
  • Temporary: Moving to my Zephyr fork that has some necessary USB/clock setup fixes. PR in Cherry pick of stm32c0 changes needed for full support with USB on v4.1 zephyr#50 will allow us to remove that temporary commit once it's merged.

You can see a test module that works with this here: https://github.com/petejohanson/stm32c0pad-module

PR check-list

  • Branch has a clean commit history
  • Additional tests are included, if changing behaviors/core code that is testable.
  • Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
  • Pre-commit used to check formatting of files, commit messages, etc.
  • Includes any necessary documentation changes.

@petejohanson petejohanson self-assigned this Dec 28, 2025
@petejohanson petejohanson requested review from a team as code owners December 28, 2025 06:16
@petejohanson petejohanson changed the title Soc/stm32c0 support SoC: stm32c0 support Dec 28, 2025
nmunnich
nmunnich reviewed Dec 30, 2025
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Code looks alright at a glance, not delving too deeply.

docs/docs/config/system.md Outdated
| `CONFIG_ZMK_DBL_TAP_BOOTLOADER` | bool | Enable the double-tap to enter bootloader functionality | y if STM32 or RP2040/RP2350 |
| `CONFIG_ZMK_DBL_TAP_BOOTLOADER_TIMEOUT_MS` | int | Duration (in ms) to wait for a second reset to enter the bootloader | 500 |

### STM32 nBOOT_SEL Option Byte Setup
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This feels like it should be a subsection of the bootloader section. Although considering the new magic value bits aren't documented under configuration, I wonder if we should have a bootloader section separate from system under config?

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@petejohanson petejohanson Dec 30, 2025

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Yeah, I'm happy to refactor and make a dedicated "Bootloader Integration" config page, if that's what you were suggesting.

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@petejohanson petejohanson Dec 30, 2025

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Fixed your other comments, will do this extraction/refactor once you respond if that was in fact your suggestion. Thanks!

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Yeah, that is indeed what I am suggesting.

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@petejohanson petejohanson Dec 30, 2025

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New page preview is up: https://deploy-preview-3174--zmk.netlify.app/docs/config/bootloader

@petejohanson petejohanson force-pushed the soc/stm32c0-support branch 4 times, most recently from 8c4d2c6 to e0b01e1 Compare December 30, 2025 23:08
nmunnich
nmunnich approved these changes Jan 3, 2026
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Couple typos, LGTM otherwise.

@petejohanson
deps: Use hal_stm32 with stm32c0 USB device fixes.
c4d3cf2 
Pull in ZMK fork of hal_stm32 with USB device driver fixes for stm32c0.
@petejohanson
feat: Add nBOOT_SEL bit setup for STM32 G0/C0 targets
742c493 
Newer STM32 C0 and G0 series SoCs do not by default allow use of the
BOOT0 pin/button to enter the bootloader once something has been flash
to the device, which is a change from previous series, and usually not
what's wanted for keyboards running ZMK. To address this, add some
optional, but default initialization code to check the nBOOT_SEL bit and
override it if necessary to ensure BOOT pin/button functionality.
@petejohanson @nmunnich
docs: Extract bootloader config into a dedicated page.
439f637 
Pull the bootloader intergration options out of the system configuration
page into their own dedicated one.

Co-authored-by: Nicolas Munnich <98408764+nmunnich@users.noreply.github.com>
@petejohanson petejohanson merged commit f85ec7e into zmkfirmware:main Jan 7, 2026
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