RTEMS | stm32f4/i2c: Implement fast mode up to 400kHz in set_bitrate (!1203)

Mon, 13 Apr 2026 01:44:35 -0700 


Mohamed Ayman created a merge request: 
https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1203

Project:Branches: mohamedayman23/rtems:fix-stm32f4-FIXME-issue-i2c to 
rtems/rtos/rtems:main
Author:   Mohamed Ayman



stm32f4/i2c: Implement fast mode up to 400kHz in set_bitrate

Previously, any bitrate above 100kHz returned RTEMS_NOT_IMPLEMENTED. Add fast 
mode support (DUTY=0, Tlow/Thigh=2) with correct CCR formula (PCLK / (3 \* br)) 
and rise time calculation (TRISE = FPCLK \* 300ns + 1), using a uint64_t cast 
to avoid 32-bit overflow.

![Screenshot from 2026-04-13 
10-37-36.png](/uploads/92e8ff124a370c63e99be0f6b4750e61/Screenshot_from_2026-04-13_10-37-36.png){width=469
 height=600}

![Screenshot from 2026-04-13 
10-42-53.png](/uploads/73656c80ace0afdf1e6bcfc5c8892a23/Screenshot_from_2026-04-13_10-42-53.png){width=900
 height=531}

AI Usage: Yes

AI Prompt: tell me the way should i think if i need to implement fast mode with 
avoiding the overflow corner cases.

AI Model: claude sonnet 4.6

How AI used: for explanation and avoid the corner cases.

-- 
View it on GitLab: 
https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1203
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