Good day guys, I need some help in troubleshooting an issue I’m having with accessing the bootloader on a Nucleo L476RG “slave” board?

I’m using a Nucleo L496ZG as the master board, with `DigitalOut` pins (`extBoot0` and `extReset`) connected to the slave’s `BOOT0` and `NRST` pins. There’s also a `Serial` instance (`usart`) on the master linked to the slave’s UART2. It appears that `BOOT1` is fixed low, so the bootloader runs instead of executing what’s in SRAM.

In `resetToBootloader`, I set `BOOT0` high, pull `NRST` low for 0.1 seconds, then bring it back high. This resets the slave and stops the program from running.

In `initBootloader`, I set up serial communication (8-bit data, even parity, 1 stop bit per AN2606) and send `0x7F` to the slave, but there’s no response. The logic analyzer shows the slave receives the data, but its TX line remains inactive.

What additional steps might be necessary to successfully start the bootloader? Below is the relevant portion of my code:

“`cpp
DigitalOut extBoot0(D7);
DigitalOut extBoot1(D6);
DigitalOut extReset(D5);

Serial usart(/* tx, rx */ D1, D0);

uint8_t rxBuffer[1];
event_callback_t serialEventCb;

void serialCb(int events) {
printf(“something happened!\n”);
}

void initBootloader() {
wait(5); // just in case?
// Once initialized the USART1 configuration is: 8-bits, even parity, and 1 Stop bit
serialEventCb.attach(serialCb);
usart.format(8, SerialBase::Even, 1);
uint8_t buffer[1024];

// write 0x7F
buffer[0] = 0x7F;
usart.write(buffer, 1, 0, 0);
printf(“sending cmd\n”);
// should ack 0x79
usart.read(rxBuffer, 1, serialEventCb, SERIAL_EVENT_RX_ALL, 0x79);
}
“`

If it’s helpful, I can provide a picture of my board setup as well.