GPS UART data written multiple times to Buffer

Question

I am receiving/reading data from a GPS module sent via USART3 to the STM32F091. The data gets there just fine which I confirm by sending it to my PC COM3 port and feeding it to 'u-center' (GPS evaulation software).

My problem is that I want to evaluate the data myself in my C program, and for that purpose I feed it into a Ring Buffer, however, every character of the GPS signal is written multiple times to the buffer, instead of one by one.

For example

GGGGGGGPPPPPPPPSSSSSSSS instead of GPS

I am unsure what I'm doing wrong, maybe it's something really obvious I'm overlooking after staring at this code so long.

Here's the relevant code.

stm32f0xx_it.c

#include <main.h>

void USART3_8_IRQHandler(void)
{
    if (USART_FLAG_RXNE != RESET)
    {
        uint16_t byte = 0;
        /* Data reception */

        /* Clear Overrun Error Flag, necessary when RXNE is used */
        USART_GetITStatus(USART3, USART_IT_ORE);

        /* Read from Receive Data Register and put into byte */
        byte = USART_ReceiveData(USART3);

        (*pRXD3).wr = ((*pRXD3).wr + 1) % (*pRXD3).max;
        (*pRXD3).Buffer[(*pRXD3).wr] = byte;

        /* Send Data to PC, and reset Transmission Complete Flag  */
        USART_GetITStatus(USART1, USART_IT_TC);
        USART_SendData(USART1, byte);

        return;
    }
    return;
}

uartGPS.h

....
    struct GPSuart
    {
        BYTE Buffer[255];
        WORD max;
        WORD re;
        WORD wr;
    };
....

main.h

....
extern volatile BYTE B_ser_txd_3[255];
extern volatile BYTE B_ser_rxd_3[255];
extern volatile struct GPSuart TXD_uart_3;
extern volatile struct GPSuart RXD_uart_3;
extern volatile struct GPSuart *pRXD3;
extern volatile struct GPSuart *pTXD3;
....

Let me know if I should provide additional information.

1) `pRXD3->wr` is clearer than `(*pRXD3).wr` 2) It looks like you obtain the value more often than it actually changes — Alexander Dmitriev, Mar 16 '18 at 09:37
@AlexanderDmitriev 1) Yea i'm still getting used to writing it like that, learned it the complicated way. 2) That's what I figured, but unfortunately I'm unsure how to prevent that, I thought the RXNE Flag would, but maybe It's just too fast. — Kater, Mar 16 '18 at 09:54

score 1 · Accepted Answer · answered Mar 16 '18 at 10:09

1

This:

if (USART_FLAG_RXNE != RESET)

does not test a flag, that code is inspecting the flag constant itself, which is not what you meant.

You need more code, to access the UART's status register and check the flag:

if (USART_GetFlagStatus(USARTx, USART_FLAG_RXNE) != RESET)

answered Mar 16 '18 at 10:09

unwind

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Well damn, I actually had it like that a couple days ago and then tried some things and apparently forgot to change it back. It works now, thanks! Now it just looks like the program never leaves the interrupt, so I can't evaluate the data. As soon as the UART_Interrupt is initialised , it jumps right into it and never even touches the next instruction. – Kater Mar 16 '18 at 10:20
Found the mistake, I enabled the Transmit Interrupt by mistake as well, so it constantly tried to Transmit. All is well now. – Kater Mar 16 '18 at 10:30

GPS UART data written multiple times to Buffer

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