FreeRTOS-Kernel/FreeRTOS/Demo/MSP430X_MSP430F5438_IAR/serial.c

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*/


/* BASIC INTERRUPT DRIVEN SERIAL PORT DRIVER.
 *
 * This is not a proper UART driver.  It only supports one port, uses loopback
 * mode, and is used to test interrupts that use the FreeRTOS API as part of
 * a wider test suite.  Nor is it intended to show an efficient implementation
 * of a UART interrupt service routine as queues are used to pass individual
 * characters one at a time!
 */

/* Standard includes. */
#include <stdlib.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "queue.h"
#include "task.h"

/* Demo application includes. */
#include "serial.h"

/* Misc. constants. */
#define serNO_BLOCK				( ( portTickType ) 0 )

/* The queue used to hold received characters. */
static xQueueHandle xRxedChars;

/* The queue used to hold characters waiting transmission. */
static xQueueHandle xCharsForTx;

/*-----------------------------------------------------------*/

xComPortHandle xSerialPortInitMinimal( unsigned portLONG ulWantedBaud, unsigned portBASE_TYPE uxQueueLength )
{
unsigned portLONG ulBaudRateCount;

	/* Initialise the hardware. */

	/* Generate the baud rate constants for the wanted baud rate. */
	ulBaudRateCount = configCPU_CLOCK_HZ / ulWantedBaud;

	portENTER_CRITICAL();
	{
		/* Create the queues used by the com test task. */
		xRxedChars = xQueueCreate( uxQueueLength, ( unsigned portBASE_TYPE ) sizeof( signed portCHAR ) );
		xCharsForTx = xQueueCreate( uxQueueLength, ( unsigned portBASE_TYPE ) sizeof( signed portCHAR ) );

		/* Reset UART. */
		UCA1CTL1 |= UCSWRST;

		/* Use SMCLK. */
		UCA1CTL1 = UCSSEL0 | UCSSEL1;
		
		/* Setup baud rate low byte. */
		UCA1BR0 = ( unsigned portCHAR ) ( ulBaudRateCount & ( unsigned portLONG ) 0xff );

		/* Setup baud rate high byte. */
		ulBaudRateCount >>= 8UL;
		UCA1BR1 = ( unsigned portCHAR ) ( ulBaudRateCount & ( unsigned portLONG ) 0xff );

		/* UCLISTEN sets loopback mode! */
		UCA1STAT = UCLISTEN;

		/* Enable interrupts. */
		UCA1IE |= UCRXIE;
		
		/* Take out of reset. */
		UCA1CTL1 &= ~UCSWRST;
	}
	portEXIT_CRITICAL();
	
	/* Note the comments at the top of this file about this not being a generic
	UART driver. */
	return NULL;
}
/*-----------------------------------------------------------*/

signed portBASE_TYPE xSerialGetChar( xComPortHandle pxPort, signed portCHAR *pcRxedChar, portTickType 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 portCHAR cOutChar, portTickType xBlockTime )
{
signed portBASE_TYPE xReturn;

	/* Send the next character to the queue of characters waiting transmission,
	then enable the UART Tx interrupt, just in case UART transmission has already
	completed and switched itself off. */
	xReturn = xQueueSend( xCharsForTx, &cOutChar, xBlockTime );
	UCA1IE |= UCTXIE;

	return xReturn;
}
/*-----------------------------------------------------------*/

/* The implementation of this interrupt is provided to demonstrate the use
of queues from inside an interrupt service routine.  It is *not* intended to
be an efficient interrupt implementation.  A real application should make use
of the DMA.  Or, as a minimum, transmission and reception could use a simple
RAM ring buffer, and synchronise with a task using a semaphore when a complete
message has been received or transmitted. */
#pragma vector=USCI_A1_VECTOR
static __interrupt void prvUSCI_A1_ISR( void )
{
signed char cChar;
portBASE_TYPE xHigherPriorityTaskWoken = pdFALSE;

	while( ( UCA1IFG & UCRXIFG ) != 0 )
	{
		/* Get the character from the UART and post it on the queue of Rxed
		characters. */
		cChar = UCA1RXBUF;
		xQueueSendFromISR( xRxedChars, &cChar, &xHigherPriorityTaskWoken );
	}
	
	/* If there is a Tx interrupt pending and the tx interrupts are enabled. */
	if( ( UCA1IFG & UCTXIFG ) != 0 )
	{
		/* The previous character has been transmitted.  See if there are any
		further characters waiting transmission. */
		if( xQueueReceiveFromISR( xCharsForTx, &cChar, &xHigherPriorityTaskWoken ) == pdTRUE )
		{
			/* There was another character queued - transmit it now. */
			UCA1TXBUF = cChar;
		}
		else
		{
			/* There were no other characters to transmit - disable the Tx
			interrupt. */
			UCA1IE &= ~UCTXIE;
		}
	}

	__bic_SR_register_on_exit( SCG1 + SCG0 + OSCOFF + CPUOFF );
	
	/* If writing to a queue caused a task to unblock, and the unblocked task
	has a priority equal to or above the task that this interrupt interrupted,
	then lHigherPriorityTaskWoken will have been set to pdTRUE internally within
	xQueuesendFromISR(), and portEND_SWITCHING_ISR() will ensure that this
	interrupt returns directly to the higher priority unblocked task.
	
	THIS MUST BE THE LAST THING DONE IN THE ISR. */	
	portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}