STM32L053C8 UART Error in Mbed2 Latter Than Rev159

[Tony-YI]

Description

I am using a STM32L053C8 MCU and got some problems with it.

#include "mbed.h"
 
int main()
{
    DigitalOut  led(PA_14);
//    Serial      serial(PB_6, PB_7);

    while(1)
    {
        led = !led;
        wait(0.1);
    }
}

The code above works fine. However, after I un-commented the Serial, the LED stop blinking. As far as I know, (PB_6, PB_7) is the UART1 serial port. I tried the UART2 and LPUART1 and both of them works fine. It looks like I can not define any UART1 port. I have tried (PA_9, PA_10) which is utilizing the UART1 and it worked. It looks like I could not define serial on (PB_6, PB_7).

According to my previous experience, I switched the mbed-2 version to Rev.159:7130f32 (I am using the online compiler) and un-commented the Serial and it worked fine.

Jerome Coutant from ST said it is because the UART1 is already used by the default STDIO.

My question is that can I disable the default STDIO and use the UART1 for my own purpose? Note that I am using the online compiler.

Thanks in advance.

Issue request type

[X] Question
[ ] Enhancement
[ ] Bug

[Tony-YI]

After I un-commented the Serial line, I probed the PB_4 pin (default LED1 on DISCO-L053C8 board) and its patterns matched the mbed_die(void) function in platform/mbed_board.c.

Referring to #6019, I have added the following code into main.cpp and tried to redirect the stdio to UART2. I have probed the pin PA_2 and it was outputting the string in printf("1\r\n");. However, once I un-commented the Serial, the MCU executed the mbed_die routine.

#include "mbed.h"

void mbed_die(void)
{
    gpio_t led_err;
    gpio_init_out(&led_err, PA_14);

    while (1) {
        for (int i = 0; i < 4; ++i) {
            gpio_write(&led_err, 1);
            wait_ms(150);
            gpio_write(&led_err, 0);
            wait_ms(150);
        }

        for (int i = 0; i < 4; ++i) {
            gpio_write(&led_err, 1);
            wait_ms(400);
            gpio_write(&led_err, 0);
            wait_ms(400);
        }
    }
}

FileHandle *mbed::mbed_override_console(int fd)
{
    static UARTSerial console(PA_2, PA_3, MBED_CONF_PLATFORM_STDIO_BAUD_RATE);
    return &console;
}
 
int main()
{
    DigitalOut  led(PA_14);
//    Serial      serial(PB_6, PB_7);

    while(1)
    {
        printf("1\r\n");
        led = !led;
        wait(0.1);
    }
}

Still looking for a way to disable the STDIO or maybe make it using the UART2.
[Mirrored to Jira]

[Tony-YI]

After some digging, it looks like it is caused by the following code in /targets/TARGET_STM/serial_api.c:

void serial_init(serial_t *obj, PinName tx, PinName rx)
{
    ...

    if ((tx == STDIO_UART_TX) || (rx == STDIO_UART_RX)) {
        stdio_config = 1;
    } else {
        if (uart_tx == pinmap_peripheral(STDIO_UART_TX, PinMap_UART_TX)) {
            error("Error: new serial object is using same UART as STDIO");
        }
    }
    ...
}

I have double checked it on mbed-dev sources, and the above code was added since Release version 159, about 6 months ago.

So I need to redefine the STDIO_UART_TX and STDIO_UART_RX.
[Mirrored to Jira]

[jeromecoutant]

Hi

Wiki page: https://os.mbed.com/teams/ST/wiki/STDIO

So I need to redefine the STDIO_UART_TX and STDIO_UART_RX.

Yes, in a mbed_app.json file like :

"target_overrides": {     
"DISCO_L053C8": {
        "target.stdio_uart_tx": "PB_6",
        "target.stdio_uart_rx": "PB_7"
    } }

[Mirrored to Jira]

[Tony-YI]

Thanks @jeromecoutant , however, since I am using the online compiler, I suppose I do not have the mbed_app.json file.

I tired to switch to mbed-cli, however, I facing the same issue mentioned here.

Currently I would like to stick to the online compiler because its .bin file is smaller than that complied using GCC_ARM.

If there is no way to redifine the STDIO_UART_TX and STDIO_UART_RX on the online compiler, I would redesign the custom board.
[Mirrored to Jira]

[jeromecoutant]

See for ex https://os.mbed.com/teams/mbed-os-examples/code/mbed-os-example-wifi/

You can add a mbed_app.json file with online compiler

[Mirrored to Jira]

[Tony-YI]

@jeromecoutant It works!!! Thanks a lot. You are really helpful!

@jeromecoutant After adding the mbed_app.json file as follows:

{
"target_overrides": {     
    "DISCO_L053C8": {
        "target.stdio_uart_tx": "PB_6",
        "target.stdio_uart_rx": "PB_7"
        }
    }
}

The macro STD_UART_TX and STD_UART_RX do change to PB_6 and PB_7. When I executed the following code, the led is blinking with 1 second interval, which means the STD_UART_TX becomes PB_6. However, when I probed the PA_9, it is outputting serial data, instead of PB_6. Moreover, once I un-comment the Serial line, the MCU is executing mbed_die() routine.

#include "mbed.h"
int main()
{
    DigitalOut  led(PA_14);

//    Serial      serial(PB_6, PB_7);
 
    while(1)
    {
        led = !led;
        printf("a\r\n");
        if(STDIO_UART_TX == PA_9)
        {
            wait(0.1);
        }
        else if(STDIO_UART_TX == PB_6)
        {
            wait(1);
        }
    }
}

[Mirrored to Jira]

[jeromecoutant]

Why do you want to re-configure PB_6 and PB_7.
Thanks to the mbed_app.json, you new serial console is already configured.

[Mirrored to Jira]

[Tony-YI]

Why do you want to re-configure PB_6 and PB_7.
Thanks to the mbed_app.json, you new serial console is already configured.

Dear @jeromecoutant, in my last comment, the line Serial serial(PB_6, PB_7) was commented. Then I probed the pin PA_9 and PB_6 respectively, and PA_9 was outputting something instead of PB_6 (mbed_app.json was added). This is contradictory to what we expect, i.e. PB_6 should output something.

In fact, I have tried (PA_14, PA_15), (PB_10, PB_11) and (PA_2, PA_3) in mbed_app.json. I must add the following code so that the corresponding TX pin could output something:

FileHandle *mbed::mbed_override_console(int fd)
{
    static UARTSerial console(STDIO_UART_TX, STDIO_UART_RX, MBED_CONF_PLATFORM_STDIO_BAUD_RATE);
    return &console;
}

However, after I added the code above and tried (PB_6, PB_7) in mbed_app.json, the MCU went into mbed_die() routine. I am sure it was caused by the code below in /targets/TARGET_STM/serial_api.c:

void serial_init(serial_t *obj, PinName tx, PinName rx)
{
    ...

    if ((tx == STDIO_UART_TX) || (rx == STDIO_UART_RX)) {
        stdio_config = 1;
    } else {
        if (uart_tx == pinmap_peripheral(STDIO_UART_TX, PinMap_UART_TX)) {
            error("Error: new serial object is using same UART as STDIO");
        }
    }
    ...
}

It looks like in serial_api.c, the STDIO_UART_TX and STDIO_UART_RX are still referring to PA_9 and PA_10 respectively.

Another interesting thing is that, I compile the above program (without FileHandle *mbed::mbed_override_console(int fd)) using mbed-cli (1.8.1) and probed the PA_9 and PB_6. None of them was outputting anything.

[Mirrored to Jira]

[adbridge]

Internal Jira reference: https://jira.arm.com/browse/IOTPART-6500

[jeromecoutant]

@Tony-YI Should we close this issue?

[wubaojun1982]

My custom board is STM32F103ZCT6, there is the same problem. After methods mentioned like above, the problem has been solved. Thx very much.