fix(usb): resolve USB CDC TX failure — DCache coherency + buffer + IMU API (bd-1lo) #6

sl-firmware · 2026-02-28T12:38:01-05:00

sl-firmware commented

2026-02-28 12:38:01 -05:00

Summary

BUG 1 (PRIMARY): SCB_DisableDCache() was inside icm42688_init(), called ~3.5s after USB starts. STM32F7 SystemInit() enables DCache; CPU writes to TX buffers stay in cache and USB hardware reads stale SRAM → sends zeros/garbage. Fix: SCB_DisableDCache() moved to main() before HAL_Init(), before USB starts.
BUG 2: CDC_Transmit() passed caller stack buffer pointer to USB hardware. USB TXFE IRQ fires async; buffer could be overwritten before FIFO is loaded. Fix: always memcpy into static UserTxBuffer before transmitting.
BUG 3: main.c called icm42688_read() directly and passed icm42688_data_t* to balance_update() which expects IMUData* (float pitch/pitch_rate). Type mismatch produced garbage balance values. Fix: use mpu6000_init()/mpu6000_read() which wraps icm42688 + complementary filter. Bonus: fix icm42688_init() returning 0 when who==0 (false IMU success).

Test plan

Flash to MAMBA F722S
Verify USB CDC port enumerates (/dev/cu.usbmodemSALTY*)
Open port with terminal — confirm JSON telemetry streams at 50Hz
Send S command — streaming toggles off/on
Confirm p (pitch) and r (pitch_rate) values are plausible
Send R command — DFU reboot works

🤖 Generated with Claude Code

## Summary - **BUG 1 (PRIMARY)**: `SCB_DisableDCache()` was inside `icm42688_init()`, called ~3.5s after USB starts. STM32F7 `SystemInit()` enables DCache; CPU writes to TX buffers stay in cache and USB hardware reads stale SRAM → sends zeros/garbage. **Fix**: `SCB_DisableDCache()` moved to `main()` before `HAL_Init()`, before USB starts. - **BUG 2**: `CDC_Transmit()` passed caller stack buffer pointer to USB hardware. USB TXFE IRQ fires async; buffer could be overwritten before FIFO is loaded. **Fix**: always `memcpy` into static `UserTxBuffer` before transmitting. - **BUG 3**: `main.c` called `icm42688_read()` directly and passed `icm42688_data_t*` to `balance_update()` which expects `IMUData*` (float pitch/pitch_rate). Type mismatch produced garbage balance values. **Fix**: use `mpu6000_init()`/`mpu6000_read()` which wraps icm42688 + complementary filter. Bonus: fix `icm42688_init()` returning 0 when `who==0` (false IMU success). ## Test plan - [ ] Flash to MAMBA F722S - [ ] Verify USB CDC port enumerates (`/dev/cu.usbmodemSALTY*`) - [ ] Open port with terminal — confirm JSON telemetry streams at 50Hz - [ ] Send `S` command — streaming toggles off/on - [ ] Confirm `p` (pitch) and `r` (pitch_rate) values are plausible - [ ] Send `R` command — DFU reboot works 🤖 Generated with [Claude Code](https://claude.com/claude-code)

sl-firmware added 1 commit 2026-02-28 12:38:02 -05:00

fix(usb): resolve USB CDC TX failure caused by three independent bugs 0bfd617c44

Bug 1 (PRIMARY — DCache/USB coherency):
SCB_DisableDCache() was buried inside icm42688_init(), called ~3.5s
after USB starts. STM32F7 DCache/USB coherency issue: when DCache is
on (enabled by SystemInit()), CPU writes to TX buffers stay in cache
and the USB hardware reads stale SRAM data. Moved SCB_DisableDCache()
to main() before HAL_Init(), ensuring coherency for all USB transfers.

Bug 2 (USB TX corruption):
CDC_Transmit() passed the caller's stack-allocated buf pointer directly
to the USB stack. The USB TXFE interrupt fires asynchronously; by then
the stack buffer may have been modified by the next loop iteration.
CDC_Transmit() now copies into the static UserTxBuffer before handing
off to the USB hardware, ensuring the buffer is stable for the transfer.

Bug 3 (IMU type mismatch → wrong data to balance):
main.c called icm42688_init()/icm42688_read() directly, passing
icm42688_data_t* (raw int16 ax/ay/az/gx/gy/gz) to balance_update()
which expects IMUData* (float pitch/pitch_rate from complementary
filter). Type mismatch produced garbage balance values. Fixed by using
mpu6000_init()/mpu6000_read() which wraps icm42688 + sensor fusion.
Telemetry updated to report fused pitch/rate instead of raw ADC counts.

Also fix icm42688_init() returning 0 on who==0 (no SPI response),
which falsely indicated IMU success.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

seb merged commit bfb94fc169 into main

2026-02-28 12:52:43 -05:00

seb referenced this issue from a commit

2026-02-28 12:52:44 -05:00

Merge pull request 'fix(usb): resolve USB CDC TX failure — DCache coherency + buffer + IMU API (bd-1lo)' (#6) from sl-firmware/bd-1lo-usb-cdc-fix into main

seb referenced this pull request

2026-02-28 13:04:37 -05:00

USB CDC TX works alone, breaks when icm42688_init() is added — needs bisect #9

sl-jetson referenced this pull request

2026-03-14 11:44:48 -04:00

feat: UWB anchor mount bracket (Issue #564) #569

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