Hello all,
We are testing LPUART wake-up from Stop 2 mode using the STM32CubeU0 LL example:
STM32Cube_FW_U0_V1.2.0/Projects/NUCLEOU083RC/Examples_LL/LPUART/LPUART_WakeUpFromStop2_Init
We made a minimal modification to the example:
- Replaced LPUART1 with LPUART2
- Used the corresponding GPIO pins for LPUART2 (PB10,PB11)
- Configuration otherwise unchanged (same clock source, wake-up on RX, interrupt-based RX)
Observed behavior on NUCLEO-U083RC
- After programming the board using STM32CubeProgrammer in hardware reset mode, the example works correctly:
- MCU enters Stop 2
- RX activity on LPUART2 wakes the system as expected
- However, after disconnecting and reconnecting the power supply LPUART2 no longer wakes the MCU from Stop 2
- RX data arrives on the pin, but no wake-up occurs
- If we again connect and disconnect the programmer (in hardware reset mode) the system starts working normally again, wake-up from Stop 2 via LPUART2 is restored
Additional observations
- Using LPUART1 instead of LPUART2, with the same configuration approach, works reliably
- The issue appears specific to LPUART2 wake-up after a cold power cycle
- The same behavior was also observed on a custom board using STM32U073CBT6
Has this behavior been observed before?
Is there any known requirement or additional reset/initialization step specific to LPUART2 for wake-up from Stop 2 after a power-on reset? I have attached the (modified) example code for your reference.
Thanks in advance for your support.
