Resolved! STM32 FDCAN: Frames visible on CANable (candump) but TX still reports ACK error — scope shows ACK notch
TL;DR: Two-node bus: STM32 (FDCAN1) ↔ CANable (SocketCAN) at 500 kbit/s candump can0 shows frames from STM32, but STM32 keeps flagging ACK error and increments TxErrorCnt. Scope on CANH/CANL (diff trace CH1–CH2) shows a dominant ACK bit in the ACK...