SO8N STM32G031C6 USART not working.

[fancyrat]

I'm trying to setup an USART for a very small MCU of the STM32G0 family, the MCU it's theoretically being programmed, but the USART is not responding, I configured the MCU just like I did in other projects (of bigger MCUs), I'm not able to find what I'm doing wrong in this case.

This is what I can see from the USART (theoretically in this image I'm sending "0xFF" all the time, but it does the same whatever I put in the buffer).

Codewise I'm enabling the USART DMA with LL_USART_EnableDMAReq_TX(USART1), then configuring with LL_DMA_ConfigAddresses.

Some checks with LL_DMA_IsEnabledChannel, and finally sending stuff with both LL_DMA_SetDataLength & LL_DMA_EnableChannel once the buffer has something on it.

Also tried to clear TC1 flag & disable channel every communication, checking it with LL_DMA_IsActiveFlag_TC1.

The USART is configured as Half-duplex (as it need to be) & baudrate, word length, etc...are correct:

[KnarfB]

And if you don't use DMA but simply write to TXD?

Is is a pin issue or a DMA prog issue?

hth

KnarfB

[fancyrat]

Hi,

I've always worked with DMA so I'm not confident in the code I've just wrote, but it seems that the same is happening.

I write this very quickly anyway, so I'll keep investigating in this direction. This is the code I've just written that doesn't use DMA.

void comms_init(void)
{
    // USART clock
    RCC->APBENR2 |= RCC_APBENR2_USART1EN;
 
    // USART baud rate
    USART1->BRR = (uint16_t)(SystemCoreClock / 115200);
 
    // USART data  (8 data bits, no parity, 1 stop bit)
    USART1->CR1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE;
 
    // USART peripheral
    USART1->CR1 |= USART_CR1_UE;
}
 
void USART_SendData(uint8_t data)
{
    // Wait for empty transmit data register 
    while (!(USART1->ISR & USART_ISR_TXFE))
        ;
 
    // Write data to the TDR
    USART1->TDR = data;
 
    // Wait for the transmission
    while (!(USART1->ISR & USART_ISR_TC))
        ;
}
 
void comms_task(void)
{
 
    while (1)
    {
        USART_SendData('H');
        USART_SendData('e');
        USART_SendData('l');
        USART_SendData('l');
        USART_SendData('o');
        USART_SendData('\r');
        USART_SendData('\n');
    }
}

[fancyrat]

EDIT: If I remove the watchdog the "spikes" that go to 0 disapear.

[KnarfB]

Your later code works* if you replace the flag with:

while (!(USART1->ISR & USART_ISR_TXE_TXFNF))

*) have added more init code for the pins, namely the auto-generated MX_USART1_UART_Init() for my STM32G031 Disco..Note that USART1_TX pin is same as BOOT0 and SWCLK, which might be confusing...

hth

KnarfB

[Viktor POHORELY]

Did you tried just simple GPIO toggling, to see if the issue comes from pin or IP ?

There are several pins in paralel on those small packages, thus in case you have other one configured as output it may not work correctly.

[fancyrat]

Thank you all,

I built the project from scratch and I manage to sent data both with the DMA & HAL, now the problem I'm having is that the data I'm receiving it's not exactly correct, I'm receiving incorrect characters, I'll try to check if with an oscilloscope, but at a simple glance, everything looks good.

Also I would try again with my old code, as @KnarfB​ confirms that it worked with a very small change.

Edit: Well I just tried with USART_SendData code and I'm still receiving weird stuff.

[fancyrat]

Just as a reference, this is what I've got now, it should be saying "HOLA" using the UART with an DMA, I'm receiving other stuff mostly random symbols, I can't seem to find the relation to it:

[fancyrat]

Now I've tried to write "*\n* just to have some other signal to compare like the one in this link: https://hackaday.com/2016/06/22/what-could-go-wrong-asynchronous-serial-edition/

It seems that in my case the message keeps repeating multiple times. But the bits are correct:

[Viktor POHORELY]

Do you have baud rate set correctly?