Countermeasures for shortening STOP bit in UART transmission processing

[Hiro]

Hello Nordic Support!

The stop bit of the last character is short in the Uart output part, and the other MPUy cannot receive the character.
How do I fix it until I send the STOP bit completely?

The waveform and the transmission program are described below.

void aUartInterface_SendData(uint8_t *data, uint16_t len)
{
    uint32_t timeout;
    uint32_t start_tick;
    uint32_t current_tick;
    uint8_t sleep = 0;
   
    if(len == 0)
        return;
   
    timeout = TIMEOUT_TICKS*len;
    start_tick = cnt_get();
   
    // check sleep or not
    if(mUartProcessing == 0)
    {
        uart_wakeup();
        sleep = 1;
    }
   
    NRF_GPIO->OUTSET = ((uint32_t)1 << PIN_UART_SENDING);
   
    NRF_UART0->TASKS_STARTTX = 1;
    for(uint16_t i=0; i<len; i++)
    {
        NRF_UART0->TXD = data[i];
        while(NRF_UART0->EVENTS_TXDRDY==0)
        {
            //
            current_tick = cnt_get();
            if( cnt_diff_compute(current_tick, start_tick) > timeout)
            {
                NRF_UART0->EVENTS_TXDRDY = 0;
                NRF_UART0->TASKS_STOPTX = 1;
                NRF_GPIO->OUTCLR = ((uint32_t)1 << PIN_UART_SENDING);
                return;
            }
        }
        NRF_UART0->EVENTS_TXDRDY = 0;
    }
    NRF_UART0->TASKS_STOPTX = 1;
   
    NRF_GPIO->OUTCLR = ((uint32_t)1 << PIN_UART_SENDING);
   
    if(sleep)
        uart_sleep();
}

let me know.

Best Regards

Hirotoshi NAGAO

CHINO Corporation

[Turbo J]

Try waiting for EVENTS_STOPPED after staring the stop task with TASKS_STOPTX;

[Hiro]

Thanks for your comments.

I use MDK ARM.
I tried to code EVENTS_TXSTOPPED, but it doesn't seem to be a member of NRF-UART0.

Compilation fails.
For sending relationships, only EVENTS_TXRDY is a member.
Is this a substitute?

[Turbo J]

My mistake - this event is only available in UARTE peripherials.

Did you configure the TX pin as "output high", i.e. set the corresponding bit to 1 in the GPIO output register?

[Jørgen Holmefjord]

Hi,

What is PIN_UART_SENDING? Is this the TX pin of the UART peripheral, or is it a separate GPIO?

Can you post the entire application so we can see the UART config and how you call this function?

Best regards,
Jørgen

[Hiro]

Hi,

The nRF52 UART cannot be used to return from an interrupt from Sleep(WFI,etc).
Between the controller MPU and the nRF52, in addition to the UART, a GPIO that can be used as an interrupt is input and one for output is assigned as a Strobe signal for UART transmission. PUN_UART_SENDING means bit 29 of GPIO.

A part of the uart initialization and configuration excerpt is described below.

Best Regard

// 構造体・enum定義.

enum
{
    RCV_STATUS_WAIT_STX = 0,
    RCV_STATUS_WAIT_LENGTH,
    RCV_STATUS_WAIT_DATA,
    RCV_STATUS_WAIT_CHECKSUM,
    RCV_STATUS_WAIT_ETX,
};

/***********************************************************************************
* CONSTANTS
*/

// 固定値.
// const型やdefineによる定数.

#if 0

#define PIN_UART_RXD 8
#define PIN_UART_TXD 6
#define PIN_UART_RTS 0
#define PIN_UART_CTS 0

#define PIN_UART_WAKEUP 30
#define PIN_UART_SENDING 29

#else

#define PIN_UART_RXD 31
#define PIN_UART_TXD 30
#define PIN_UART_RTS 0
#define PIN_UART_CTS 0

#define PIN_UART_WAKEUP 28
#define PIN_UART_SENDING 29

#endif

#define STX 0x02
#define ETX 0x03

static void uart_sleep(void)
{
    NRF_UART0->ENABLE = 0;
   
    NRF_UART0->TASKS_STOPRX = 1;
    NRF_UART0->INTENCLR = (1<<2);   // RX Ready,
   
    NRF_UART0->EVENTS_RXDRDY = 0;
    sd_nvic_ClearPendingIRQ(UART0_IRQn);
   
    NRF_UART0->PSELRXD = 0xFFFFFFFF;
    NRF_UART0->PSELTXD = 0xFFFFFFFF;
   
    // GPIO
    //nrf_gpio_cfg_input(PIN_UART_TXD, NRF_GPIO_PIN_NOPULL);          // 80uA程度, 0出力なし (DK).
    //nrf_gpio_cfg_input(PIN_UART_RXD, NRF_GPIO_PIN_NOPULL);
    //nrf_gpio_cfg_input(PIN_UART_TXD, NRF_GPIO_PIN_PULLDOWN);  // 3uA未満, 0出力あり (DK).
    //nrf_gpio_cfg_input(PIN_UART_RXD, NRF_GPIO_PIN_PULLDOWN);
//    nrf_gpio_cfg_input(PIN_UART_TXD, NRF_GPIO_PIN_PULLUP);  // 3uA未満, 0出力なし (DK).
    nrf_gpio_cfg_input(PIN_UART_RXD, NRF_GPIO_PIN_PULLUP);
   
    mUartProcessing = 0;
}

static void uart_wakeup(void)
{
    // GPIO
    nrf_gpio_cfg_output(PIN_UART_TXD);
    nrf_gpio_cfg_input(PIN_UART_RXD, NRF_GPIO_PIN_NOPULL);
   
    NRF_UART0->PSELRXD = PIN_UART_RXD;
    NRF_UART0->PSELTXD = PIN_UART_TXD;
   
    NRF_UART0->INTENSET = (1<<2);   // RX Ready,
    NRF_UART0->ENABLE = 4;
   
    NRF_UART0->TASKS_STARTRX = 1;
   
    NRF_UART0->EVENTS_RXDRDY = 0;
    sd_nvic_ClearPendingIRQ(UART0_IRQn);
   
    mUartProcessing = 1;
}

void checkGPIO(void)
{
    if(nrf_gpio_pin_read(PIN_UART_WAKEUP)==0)
    {
       
        NRF_LOG_INFO("Wake up is Low");
       
        // goto sleep
        nrf_gpio_cfg_sense_input(PIN_UART_WAKEUP, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_HIGH);
        uart_sleep();
       
        //cnt_stop();   //
    }
    else
    {
        NRF_LOG_INFO("Wake up is High");
       
        // wakeup
        nrf_gpio_cfg_sense_input(PIN_UART_WAKEUP, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);
        uart_wakeup();
       
        cnt_start();
    }
}

/***********************************************************************************
* GLOBAL FUNCTIONS
*/

// グローバル関数.

void aUartInterface_Init()
{
   
    mUartCmdRecv = 0;
    mUartProcessing = 0;
   
    mRecvLen = 0;
    mRecvBufIndx = 0;
   
    // GPIO
    /*
    NRF_GPIO->DIRSET = ((uint32_t)1 << PIN_UART_SENDING);
    NRF_GPIO->DIRCLR = (1 << PIN_UART_WAKEUP);
    */
    nrf_gpio_cfg_output(PIN_UART_SENDING);
    nrf_gpio_cfg_input(PIN_UART_WAKEUP, NRF_GPIO_PIN_NOPULL);
   
    // GPIOTE
    nrf_gpio_cfg_sense_input(PIN_UART_WAKEUP, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_HIGH);
    NRF_GPIOTE->INTENSET = GPIOTE_INTENSET_PORT_Msk;
    sd_nvic_SetPriority(GPIOTE_IRQn, APP_IRQ_PRIORITY_LOW);
    sd_nvic_EnableIRQ(GPIOTE_IRQn);
   
    // UART.
    /*
    NRF_GPIO->DIRSET = (1<<PIN_UART_TXD);
    NRF_GPIO->DIRCLR = (1<<PIN_UART_RXD);
    */
    nrf_gpio_cfg_output(PIN_UART_TXD);
    nrf_gpio_cfg_input(PIN_UART_RXD, NRF_GPIO_PIN_NOPULL);
   
    NRF_UART0->PSELRXD = PIN_UART_RXD;
    NRF_UART0->PSELTXD = PIN_UART_TXD;
   
    //NRF_UART0->BAUDRATE = UART_BAUDRATE_BAUDRATE_Baud57600;
    NRF_UART0->BAUDRATE = UART_BAUDRATE_BAUDRATE_Baud9600;
   
    NRF_UART0->INTENSET = (1<<2);   // RX Ready,
   
    NRF_UART0->ENABLE = 4;
   
    sd_nvic_SetPriority(UART0_IRQn, APP_IRQ_PRIORITY_LOW);
    sd_nvic_EnableIRQ(UART0_IRQn);
   
    // timeout
    cnt_init();
   
    // check GPIO
    checkGPIO();
}