UART on expansion board 1LC

[JoA-RHU]

Hi,

I'm trying to implement a serial communication on the TOOL1LC firmware (v3.5.3) using pins PA09 and PA12 (io0.in/out). So far, I managed to transmit what I want from the board, but I can't receive proper data and I don't understand why.

Regarding the ports configuration and serial initialization this is what I've done:

void SerialPortInit(AsyncSerial*) noexcept
{
    SetPinFunction(PortAPin(9), GpioPinFunction::D); // Rx on PA09, sercom 2, pad 1
    SetPinFunction(PortAPin(12), GpioPinFunction::C); // Tx on PA12, sercom 2, pad 0
}
 
void SerialPortDeinit(AsyncSerial*) noexcept
{
    pinMode(PortAPin(9), PinMode::PIN_MODE_NOT_CONFIGURED);
    pinMode(PortAPin(12), PinMode::PIN_MODE_NOT_CONFIGURED);
}
 
AsyncSerial uart0(2, 1, 128, 128, SerialPortInit, SerialPortDeinit);
 
extern "C" void SERCOM2_Handler()
{
    uart0.Interrupt();
}
 

Then, uart0 is used in a handler to send and read data periodically (it is spinning in the heating task, so every 250ms).

Sending data works perfectly with method uart0.write(..), but when data is uart0.available() I get only 0s (null) when I uart0.read().

I know uart is officially not supported on expansion boards, but this is the only option I have to communicate with the device I want to use. And I don't have the knowledge to build a completely new expansion board using a SammyC21, in terms of electronics.

Any help or hint would be greatly appreciated.
Thanks

[dc42]

@JoA-RHU I don't know whether this is the cause of your issue, however you also need to set the priority of the UART interrupt to NvicPriorityUart. This is normally done in Platform::InitialiseInterupts.

[JoA-RHU]

@dc42 Indeed, this is done in Platform::InitialiseInterupts like that:

...
#elif SAMC21
		NVIC_SetPriority(StepTcIRQn, NvicPriorityStep);
		NVIC_SetPriority(CAN0_IRQn, NvicPriorityCan);
# if NUM_SERIAL_PORTS >= 1
		NVIC_SetPriority(Serial0_IRQn, NvicPriorityUart);
# endif
...
 

And I've defined Serial0_IRQn as SERCOM2_IRQn.

[dc42]

@JoA-RHU What baud rate are you using? There is a 10K/2n2 deglitch filter formed by R4 and C28 on IO0_IN. The time constant is 22us so baud rates above 9600 or perhaps 19200 are unlikely to work.

[JoA-RHU]

@dc42 I see... I was trying to use the default baud rate of the device I communicate with, which is 57600. I tested with 9600 and it seems much better!
Thank you very much! I would never have thought of such a thing...