signed portBASE_TYPE uart0PutChar (signed portCHAR cOutChar, portTickType xBlockTime)
{
  signed portBASE_TYPE xReturn = 0;

  portENTER_CRITICAL ();
  {
    //
    //  Is there space to write directly to the UART?
    //
    if (*plTHREEmpty0 == (portLONG) pdTRUE)
    {
      *plTHREEmpty0 = pdFALSE;
      UART0_THR = cOutChar;
      xReturn = pdPASS;
    }
    else
    {
      //
      //  We cannot write directly to the UART, so queue the character.  Block for a maximum of
      //  xBlockTime if there is no space in the queue.
      //
      xReturn = xQueueSend (xTX0Queue, &cOutChar, xBlockTime);

      //
      //  Depending on queue sizing and task prioritisation:  While we were blocked waiting to post
      //  interrupts were not disabled.  It is possible that the serial ISR has emptied the Tx queue,
      //  in which case we need to start the Tx off again.
      //
      if ((*plTHREEmpty0 == (portLONG) pdTRUE) && (xReturn == pdPASS))
      {
        xQueueReceive (xTX0Queue, &cOutChar, serNO_BLOCK);
        *plTHREEmpty0 = pdFALSE;
        UART0_THR = cOutChar;
      }
    }
  }

  portEXIT_CRITICAL ();

  return xReturn;
}

void vPortEnterCritical( void )
{
    /* Disable interrupts as per portDISABLE_INTERRUPTS();                             */
    asm volatile (
        "STMDB    SP!, {R0}            \n\t"    /* Push R0.                                */
        "MRS    R0, CPSR            \n\t"    /* Get CPSR.                            */
        "ORR    R0, R0, #0xC0        \n\t"    /* Disable IRQ, FIQ.                    */
        "MSR    CPSR, R0            \n\t"    /* Write back modified value.            */
        "LDMIA    SP!, {R0}" );                /* Pop R0.                                */

    /* Now interrupts are disabled ulCriticalNesting can be accessed
    directly.  Increment ulCriticalNesting to keep a count of how many times
    portENTER_CRITICAL() has been called. */
    ulCriticalNesting++;
}

if( xTicksToWait > ( portTickType ) 0 )
{
    vTaskSuspendAll();

    if( prvIsQueueFull( pxQueue ) )
    {
        if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
        {
            if( !xTaskResumeAll() )
            {
                taskYIELD();
            }
        }
        else
        {
            ( void ) xTaskResumeAll();
        }
    }
    else
    {
        ( void ) xTaskResumeAll();
    }
}