text: /*
   * FreeRTOS Kernel V10.1.0
   * Copyright (C) 2018 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy of
   * this software and associated documentation files (the "Software"), to deal in
   * the Software without restriction, including without limitation the rights to
   * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
   * the Software, and to permit persons to whom the Software is furnished to do so,
   * subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in all
   * copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
   * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
   * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   *
   * http://www.FreeRTOS.org
   * http://aws.amazon.com/freertos
   *
   * 1 tab == 4 spaces!
   */
  
  /* BASIC INTERRUPT DRIVEN SERIAL PORT DRIVER.   
   * 
   * This file only supports UART 0
   */
  
  /* Standard includes. */
  #include <stdlib.h>
  
  /* Scheduler includes. */
  #include "FreeRTOS.h"
  #include "queue.h"
  #include "task.h"
  
  /* Demo application includes. */
  #include "serial.h"
  
  /* The queue used to hold received characters. */
  static QueueHandle_t			xRxedChars;
  
  /* The queue used to hold characters waiting transmission. */
  static QueueHandle_t			xCharsForTx;
  
  static volatile short	sTHREEmpty;
  
  static volatile short	queueFail = pdFALSE;
  
  /*-----------------------------------------------------------*/
  xComPortHandle xSerialPortInitMinimal( unsigned long ulWantedBaud, unsigned portBASE_TYPE uxQueueLength )
  {
  	/* Initialise the hardware. */
  	portENTER_CRITICAL();
  	{
  		/* Create the queues used by the com test task. */
  		xRxedChars = xQueueCreate( uxQueueLength, ( unsigned portBASE_TYPE ) sizeof(signed char) );
  		xCharsForTx = xQueueCreate( uxQueueLength, ( unsigned portBASE_TYPE ) sizeof(signed char) );
  
  		if( xRxedChars == 0 )
  		{
  			queueFail = pdTRUE;
  		}
  
  		if( xCharsForTx == 0 )
  		{
  			queueFail = pdTRUE;
  		}
  
  		/* Initialize UART asynchronous mode */
  		BGR0 = configCLKP1_CLOCK_HZ / ulWantedBaud;
  
  		SCR0 = 0x17;	/* 8N1 */
  		SMR0 = 0x0d;	/* enable SOT3, Reset, normal mode */
  		SSR0 = 0x02;	/* LSB first, enable receive interrupts */
  
  		PIER08_IE2 = 1; /* enable input */
  		DDR08_D2 = 0;	/* switch P08_2 to input */
  		DDR08_D3 = 1;	/* switch P08_3 to output */
  	}
  	portEXIT_CRITICAL();
  
  	/* Unlike other ports, this serial code does not allow for more than one
  	com port.  We therefore don't return a pointer to a port structure and can
  	instead just return NULL. */
  	return NULL;
  }
  /*-----------------------------------------------------------*/
  
  signed portBASE_TYPE xSerialGetChar( xComPortHandle pxPort, signed char *pcRxedChar, TickType_t xBlockTime )
  {
  	/* Get the next character from the buffer.  Return false if no characters
  	are available, or arrive before xBlockTime expires. */
  	if( xQueueReceive(xRxedChars, pcRxedChar, xBlockTime) )
  	{
  		return pdTRUE;
  	}
  	else
  	{
  		return pdFALSE;
  	}
  }
  /*-----------------------------------------------------------*/
  
  signed portBASE_TYPE xSerialPutChar( xComPortHandle pxPort, signed char cOutChar, TickType_t xBlockTime )
  {
  signed portBASE_TYPE	xReturn;
  
  	/* Transmit a character. */
  	portENTER_CRITICAL();
  	{
  		if( sTHREEmpty == pdTRUE )
  		{
  			/* If sTHREEmpty is true then the UART Tx ISR has indicated that 
  			there are no characters queued to be transmitted - so we can
  			write the character directly to the shift Tx register. */
  			sTHREEmpty = pdFALSE;
  			TDR0 = cOutChar;
  			xReturn = pdPASS;
  		}
  		else
  		{
  			/* sTHREEmpty is false, so there are still characters waiting to be
  			transmitted.  We have to queue this character so it gets 
  			transmitted	in turn. */
  
  			/* Return false if after the block time there is no room on the Tx 
  			queue.  It is ok to block inside a critical section as each task
  			maintains it's own critical section status. */
  			if( xQueueSend(xCharsForTx, &cOutChar, xBlockTime) == pdTRUE )
  			{
  				xReturn = pdPASS;
  			}
  			else
  			{
  				xReturn = pdFAIL;
  			}
  		}
  
  		if( pdPASS == xReturn )
  		{
  			/* Turn on the Tx interrupt so the ISR will remove the character from the
  			queue and send it.   This does not need to be in a critical section as
  			if the interrupt has already removed the character the next interrupt
  			will simply turn off the Tx interrupt again. */
  			SSR0_TIE = 1;
  		}
  	}
  	portEXIT_CRITICAL();
  
  	return pdPASS;
  }
  /*-----------------------------------------------------------*/
  
  /*
   * UART RX interrupt service routine.
   */
  __interrupt void UART0_RxISR( void )
  {
  volatile signed char	cChar;
  portBASE_TYPE xHigherPriorityTaskWoken = pdFALSE;
  
  	/* Get the character from the UART and post it on the queue of Rxed 
  	characters. */
  	cChar = RDR0;
  
  	xQueueSendFromISR( xRxedChars, ( const void *const ) &cChar, &xHigherPriorityTaskWoken );
  
  	if( xHigherPriorityTaskWoken )
  	{
  		/*If the post causes a task to wake force a context switch 
  		as the woken task may have a higher priority than the task we have 
  		interrupted. */
  		portYIELD_FROM_ISR();
  	}
  }
  /*-----------------------------------------------------------*/
  
  /*
   * UART Tx interrupt service routine.
   */
  __interrupt void UART0_TxISR( void )
  {
  signed char			cChar;
  signed portBASE_TYPE	xTaskWoken = pdFALSE;
  
  	/* The previous character has been transmitted.  See if there are any
  	further characters waiting transmission. */
  	if( xQueueReceiveFromISR(xCharsForTx, &cChar, &xTaskWoken) == pdTRUE )
  	{
  		/* There was another character queued - transmit it now. */
  		TDR0 = cChar;
  	}
  	else
  	{
  		/* There were no other characters to transmit. */
  		sTHREEmpty = pdTRUE;
  
  		/* Disable transmit interrupts */
  		SSR0_TIE = 0;
  	}
  }
  