Unreliable UART

Help
1

Hello everyone,

I am having a hard time with communicating between a LoRa e5 mini board and something else (PC, RPi, Arduino) using UART.

Here is an output example :

hello from board
this is a very very very very long string, because i feel like it
well hello too
well helo too
that's a pretty long line too
that's a petty long line too
0123456789876543210
012345679876543210

Two first lines are issued from my board, then it is a line I am sending, and the line echoed back to me. It seems the problem is on the board reading side, but I can’t see what I am missing.

Here is the code that generated said output :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "ztimer.h"
#include "stdio_base.h"

int main(void)
{
    stdio_init();

    size_t max_len = 240;
    char msg[max_len];

    stdio_write("hello from board\n", 17);
    stdio_write("this is a very very very very long string, because i feel like it\n", 66);

    while (1) {
        //checking for input data
        if (stdio_available()) {

            //wait a bit, making sure we get everything
            ztimer_sleep(ZTIMER_MSEC, 10);

            //read and print back
            ssize_t count = stdio_read(&msg, max_len);

            for (int i = 0; i < count; i++) {
                printf("%c", msg[i]);
            }
            printf("\n");
        }
        ztimer_sleep(ZTIMER_MSEC, 1);
    }
    return 0;
}

To connect to the board I tried pyterm, my own python script, the Arduino IDE Serial monitor, they all encounter this problem.

Interestingly, when I try tests/drivers/sx126x which includes a shell to try sx126x features, my input is correctly read, so I guess the problem is on some coding on parameters missing rather on RIOT OS itself

Does anybody have a clue ?

Edit : another (smallish) problem I encounter is it seems my data is not sent (from the board) until I send a \n I tried both printf and stdio_write, both seems to need that \n

2

Something seems off about the example code and output given. Your example code inserts newlines \n, but those are not showing up in the example output.

Also, stdio_read() is blocking. I don’t think you should need the calls to ztimer_sleep() for that reason.

3

Solved. Pasting my code for anyone that could need it :

#include <stdio.h>
#include "ztimer.h"
#include "stdio_base.h"


int main(void)
{
    stdio_init();

    size_t max_size = 256;
    char buffer[max_size];
    size_t current_size = 0;
    uint32_t timestamp = 0;

    while (1) {

        while (stdio_available()) {

            //read byte after byte, store it in buffer[]
            char c;
            ssize_t count = stdio_read(&c, 1);
            buffer[current_size] = c;
            current_size += count;

            timestamp = ztimer_now(ZTIMER_MSEC);
        }

        //no new data since 10ms, let's do something with it
        if (current_size > 0 && ztimer_now(ZTIMER_MSEC) - timestamp > 10) {
            stdio_write(buffer, current_size);

            //reset buffer
            current_size = 0;
        }

    }
    return 0;
}

There might be a better way to do it, but this works for me.

4

There is no need to call stdio_init() yourself, it’s already called in early_init(). You can also just use getchar() or shell_readline().