Question
STM32MP257F-EV1 stopped booting after MDF1/SAI2 rework: rails OK, NRST OK, no Boot ROM UART or USB response
Product / board: STM32MP257F-EV1, MB1936 revision, configuration [A35-TD or M33-TD]
Summary
The board worked for one session after two hardware changes, then stopped booting. LD6, LD5 and LD11 light. LD3 and LD4 do not. The Boot ROM gives no response over UART or USB.
What was changed
- A PDM microphone was wired to PA6/PA7 by a wire tap at R169/R175 (MDF1). This was our own design decision, not based on any ST recommendation.
- A MAX98357A speaker amplifier was added on SAI2A (PJ11, PJ3, PJ12 at AF4), with matching device-tree changes.
What I have checked
| Check | Result |
|---|---|
| NRST (B1) | 3.3 V idle, 0 V pressed, 3.3 V after release |
| VDDIO | 3.3 V |
| 1V8 | 1.8 V |
| VDDCPU | 0.8 V |
| VDDCORE | 0.8 V |
| VDDGPU | 0 V (not treated as a fault) |
| VDD_DDR | 0.037 V (not treated as a fault) |
| VDDA1V8_AON | 1.8 V |
| VDD3V3USB | 3.3 V |
| HSE | Not checked; no accessible probe point |
Boot ROM tests (SW1 all OPEN)
STM32_Programmer_CLI -ldetects the ST-LINK V3.-c port=/dev/ttyACM0 br=115200and-c port=/dev/ttyACM1 br=115200both open and then fail: “Timeout error occured while waiting for acknowledgement. Error: Activating device: KO.”- With USB DRD connected, no DFU device enumerates on the host.
Not yet done
Peripherals disconnected (mic wires, MAX98357A, speaker); boot of an unmodified ST sample microSD image.
Questions
- The main rails and NRST look normal, but the Boot ROM gives no UART acknowledgement and no USB enumeration. What could cause this on the EV1?
- Could the PA6/PA7 tap (shared with ETH3 TXD0/TXD1) or the SAI2 wiring interfere with Boot ROM serial download?
- Is there a recommended recovery procedure, or a test point for the HSE clock?
Thanks & Regards,
Radha