Two UARTs on MCU: FreeRTOS required (or wise)?

Question

I want to use a small stm32G0 with two UARTs:

• one RX receiving ~300 bytes from RFID reader, around once per second, 115kbaud. I parse the message to simple Modbus data every time I receive it (CRC check involved)
• one with RX receiving a 8 byte request (Modbus) every second and a TX calculating a CRC and sending out a 40 bytes response after 30-200ms (Modbus). 9600baud.

Furthermore there are no tasks.

I understand this can be done using FreeRTOS, but I am new to that, will figure it out though, but I wonder whether it could ever be as stable as when keeping it simple. But I have to admit, I have not figured out how I could keep this simple:

• receive a 300 byte message around every second (not fixed), check CRC16, parsing out about 10 floating point values (in ascii), convert those to IEEE754 floating points, ready to be requested (some of them, or all of them)
• listen on the other RX for incoming Modbus request, retrieve the 1-10 floating point values, create a (=simple) message and calculate CRC16

Question I have is whether it can be even be done without freeRTOS. And if so, whether it is advisable.

Answer 1

You probably don't need RTOS for this project.

There are 3 main parts:

1. Some logic to fill RFID RX buffer, using DMA and/or interrupts
2. Some logic to fill Modbus RX buffer, using DMA and/or interrupts
3. The main loop :

do forever {
    Process RFID RX buffer, parse text
    Possibly update Modbus registers using the parsed values
    Process Modbus RX buffer, arm USART TX DMA with the response
}

If this loop can execute before the Modbus master times out or before the RFID reader sends another package, you're done. If not, you can move your Modbus processing (which probably has tighter timing requirements than RFID) into an ISR. Normally, it's not a good idea to do time consuming work in ISR, but in your case I think it's okay considering that your uC doesn't have much to do.