TM4C123GH6PM: Flushing UART Transmit Buffer

No, that function checks to see that the FIFO full flag is not set before writing the character. When FIFO mode is disabled, the FIFO full flag represents the state of the holding register. The source for that function is in the file "C:\ti\TivaWare_C_Series-2.1.4.178\driverlib\uart.c". I have included a copy of the function below.

This is one of the rare cases where what you want to do is not supported by the TivaWare library. You could write your own function that does the HWREG write without checking the FIFO full flag.

//*****************************************************************************
//
//! Sends a character to the specified port.
//!
//! \param ui32Base is the base address of the UART port.
//! \param ucData is the character to be transmitted.
//!
//! This function writes the character \e ucData to the transmit FIFO for the
//! specified port.  This function does not block, so if there is no space
//! available, then a \b false is returned and the application must retry the
//! function later.
//!
//! \return Returns \b true if the character was successfully placed in the
//! transmit FIFO or \b false if there was no space available in the transmit
//! FIFO.
//
//*****************************************************************************
bool
UARTCharPutNonBlocking(uint32_t ui32Base, unsigned char ucData)
{
    //
    // Check the arguments.
    //
    ASSERT(_UARTBaseValid(ui32Base));

    //
    // See if there is space in the transmit FIFO.
    //
    if(!(HWREG(ui32Base + UART_O_FR) & UART_FR_TXFF))
    {
        //
        // Write this character to the transmit FIFO.
        //
        HWREG(ui32Base + UART_O_DR) = ucData;

        //
        // Success.
        //
        return(true);
    }
    else
    {
        //
        // There is no space in the transmit FIFO, so return a failure.
        //
        return(false);
    }
}