MSP432P401R: UART Comms stalls because UCTXIFG is clear after a character is sent.

Julian,

  Can you send a code snippet that would reliably exercise the problem you are seeing?

Regards,

  Bob Landers.

G'Day Bob,

The code below is a modified version of the uart_loopback_24mhz_brclk example that comes with Simplelink, modified to exhibit the problem I've described. 

Fire up CCS, run the program on your MSP432 Launchpad.  Open a terminal program and connect to the second serial port on the Launchpad and you should see characters spewing out in ASCII order.  Now, in the terminal program, hammer the keyboard.  Hits lots of keys rapidly.  It might take a minute or so, but eventually you will see the output from the launchpad stop.  Now pause execution in the debugger and have a look at register EUSCI_A0 UCTXIFG.  It will be low when it shouldn't be.  Set it back to high and  characters will start being transmitted again.

// For brevity, snip TI disclaimer.

/* DriverLib Includes */
#include <ti/devices/msp432p4xx/driverlib/driverlib.h>

/* Standard Includes */
#include <stdint.h>
#include <stdbool.h>
#include <ti/drivers/utils/RingBuf.h>

/* UART Configuration Parameter. These are the configuration parameters to
 * make the eUSCI A UART module to operate with a 115200 baud rate. These
 * values were calculated using the online calculator that TI provides
 * at:
 * software-dl.ti.com/.../index.html
 */
const eUSCI_UART_Config uartConfig =
{
        EUSCI_A_UART_CLOCKSOURCE_SMCLK,          // SMCLK Clock Source
        13,                                      // BRDIV = 13
        0,                                       // UCxBRF = 0
        37,                                      // UCxBRS = 37
        EUSCI_A_UART_NO_PARITY,                  // No Parity
        EUSCI_A_UART_LSB_FIRST,                  // MSB First
        EUSCI_A_UART_ONE_STOP_BIT,               // One stop bit
        EUSCI_A_UART_MODE,                       // UART mode
        EUSCI_A_UART_OVERSAMPLING_BAUDRATE_GENERATION  // Oversampling
};

RingBuf_Object ringbuf_hndl;
uint8_t txChar_u8 = 0;
uint8_t rxBuff_u8;

int main(void)
{
    /* Halting WDT  */
    MAP_WDT_A_holdTimer();

    /* Selecting P1.2 and P1.3 in UART mode and P1.0 as output (LED) */
    MAP_GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P1,
             GPIO_PIN2 | GPIO_PIN3, GPIO_PRIMARY_MODULE_FUNCTION);
    MAP_GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);
    MAP_GPIO_setOutputLowOnPin(GPIO_PORT_P1, GPIO_PIN0);

    /* Setting DCO to 24MHz (upping Vcore) */
    FlashCtl_setWaitState(FLASH_BANK0, 2);
    FlashCtl_setWaitState(FLASH_BANK1, 2);
    MAP_PCM_setCoreVoltageLevel(PCM_VCORE1);
    CS_setDCOCenteredFrequency(CS_DCO_FREQUENCY_24);

    /* Configuring UART Module */
    MAP_UART_initModule(EUSCI_A0_BASE, &uartConfig);

    /* Enable UART module */
    MAP_UART_enableModule(EUSCI_A0_BASE);

    /* Enabling interrupts */
    MAP_UART_enableInterrupt(EUSCI_A0_BASE, EUSCI_A_UART_RECEIVE_INTERRUPT);
    MAP_UART_enableInterrupt(EUSCI_A0_BASE, EUSCI_A_UART_TRANSMIT_INTERRUPT);
    MAP_Interrupt_enableInterrupt(INT_EUSCIA0);
    MAP_Interrupt_enableSleepOnIsrExit();

    // Prime the Tx pump.  Once this char is sent the UCTXIFG interrupt
    // will keep characters flowing out.
    MAP_UART_transmitData(EUSCI_A0_BASE, 'a');

    while(1)
    {
    }
}


void EUSCIA0_IRQHandler(void)
{
    uint_fast8_t status_u8 = MAP_UART_getEnabledInterruptStatus(EUSCI_A0_BASE);
    uint_fast8_t flags_u8;
    uint8_t rx_char_u8;

    if(status_u8 & EUSCI_A_UART_RECEIVE_INTERRUPT_FLAG)
    {
      MAP_UART_clearInterruptFlag(EUSCI_A0_BASE, EUSCI_A_UART_RECEIVE_INTERRUPT);

      flags_u8 = MAP_UART_queryStatusFlags(EUSCI_A0_BASE, EUSCI_A_UART_FRAMING_ERROR + EUSCI_A_UART_OVERRUN_ERROR + EUSCI_A_UART_PARITY_ERROR + EUSCI_A_UART_BREAK_DETECT + EUSCI_A_UART_RECEIVE_ERROR);
      rx_char_u8 = MAP_UART_receiveData(EUSCI_A0_BASE);

      if (!flags_u8)
      {
        // Put received char in a buffer for processing elsewhere
        rxBuff_u8 =  rx_char_u8;
      }
    }


    if(status_u8 & EUSCI_A_UART_TRANSMIT_INTERRUPT)
    {
      // Don't bother clearing the Tx interrupt flag here!  Its hardware controlled.
      MAP_UART_transmitData(EUSCI_A0_BASE, txChar_u8++);
    }
}