This document describes a "Hello World" example using FreeRTOS on an embedded operating system. It creates two tasks, a Tx task that sends the string "Hello World" to a queue every second, and an Rx task that receives the string from the queue and prints it. A timer is also created that expires after 10 seconds, checks if the Rx task has received enough messages, and prints whether the example passed or failed before deleting the two tasks.

1. Embedded Operating System:
FreeRTOS: Hello World!
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2. Hello World Example in Xilinx Vivado SDK
(FreeRTOS)
/* FreeRTOS includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include "timers.h"
/* Xilinx includes. */
#include "xil_printf.h"
#include "xparameters.h"
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3. #define TIMER_ID 1
#define DELAY_10_SECONDS 10000UL
#define DELAY_1_SECOND 1000UL
#define TIMER_CHECK_THRESHOLD 9
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4. /* The Tx and Rx tasks as described at the top of this file. */
static void prvTxTask( void *pvParameters );
static void prvRxTask( void *pvParameters );
static void vTimerCallback( TimerHandle_t pxTimer );
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5. /* The queue used by the Tx and Rx tasks, as described at the top of this file. */
static TaskHandle_t xTxTask;
static TaskHandle_t xRxTask;
static QueueHandle_t xQueue = NULL;
static TimerHandle_t xTimer = NULL;
char HWstring[15] = "Hello World";
long RxtaskCntr = 0;
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6. int main( void )
{
/* pdMS_TO_TICKS: Converts a time in milliseconds to a time in ticks. */
const TickType_t x10seconds = pdMS_TO_TICKS(DELAY_10_SECONDS );
xil_printf( "Hello from Freertos example mainrn" );
xTaskCreate( prvTxTask, ( const char * ) "Tx",
configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY, &xTxTask );
xTaskCreate( prvRxTask, ( const char * ) "GB",
configMINIMAL_STACK_SIZE, NULL, tskIDLE_PRIORITY + 1, &xRxTask );
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7. xTaskCreate( prvTxTask, ( const char * ) "Tx",
configMINIMAL_STACK_SIZE, NULL,
tskIDLE_PRIORITY, &xTxTask );
/* prvTxTask : function that implements the task */
/* “TX” : Name for the task */
/* configMINIMAL_STACK_SIZE : stack allocated tot he task */
/* NULL : parameter not used */
/* tskIDLE_PRIORITY : task runs at idle priority */
/* &xTxTask : TX Taskhandler */
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8. xTaskCreate( prvRxTask, ( const char * ) "GB",
configMINIMAL_STACK_SIZE, NULL,
tskIDLE_PRIORITY + 1, &xRxTask );
/* prvRxTask : function that implements the task */
/* “GB” : Name for the task */
/* configMINIMAL_STACK_SIZE : stack allocated tot he task */
/* NULL : parameter not used */
/* tskIDLE_PRIORITY : task runs at idle priority +1 */
/* &xRxTask : RX Taskhandler */
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9. xTaskCreate( prvRxTask, ( const char * ) "GB", configMINIMAL_STACK_SIZE,
NULL, tskIDLE_PRIORITY + 1, &xRxTask );
xQueue = xQueueCreate(1, sizeof( HWstring ) );
/* Check if queue was created */
configASSERT(xQueue);
xTimer = xTimerCreate( (const char *) "Timer", x10seconds, pdFALSE, (void *)
TIMER_ID, vTimerCallback);
configASSERT(xTimer);
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10. xQueue = xQueueCreate(1, sizeof( HWstring ) );
/* 1 : One place in queue */
/* sizeof (HWstring) : place in queue can hold HWstring */
/* char HWstring[15] : “Hello World”; */
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11. xTimer = xTimerCreate( (const char *) "Timer",
x10seconds, pdFALSE, (void *) TIMER_ID,
vTimerCallback);
/* “Timer” : Name of Timer */
/* x10seconds : expires after 10 seconds */
/* pdFALSE : Don’t autoreload */
/* TIMER_ID : Timer identifier */
/* vTimerCallback : Timer callback function */
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12. prvRxTask
static void prvRxTask( void *pvParameters )
{
char Recdstring[15] = "";
for( ;; )
{
xQueueReceive( xQueue, Recdstring, portMAX_DELAY );
xil_printf( "Rx task received string from Tx task: %srn", Recdstring );
RxtaskCntr++;
}
}
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13. xQueueReceive( xQueue, Recdstring,
portMAX_DELAY );
/* xQueue : Queue being read */
/* Recdstring : Data read intro this address */
/* portMAX_DELAY : wait without timeout for data */
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14. prvTxTask
static void prvTxTask( void *pvParameters )
{
const TickType_t x1second = pdMS_TO_TICKS( DELAY_1_SECOND );
for( ;; )
{
/* Delay for 1 second. */
vTaskDelay( x1second );
xQueueSend( xQueue, HWstring, 0UL );
}
}
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15. xQueueSend( xQueue, HWstring, 0UL );
/* xQueue : Queue written to */
/* Hwstring : Address data being sent */
/* 0UL : block time */
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16. vTimerCallback
static void vTimerCallback( TimerHandle_t pxTimer )
{
long lTimerId;
configASSERT( pxTimer );
lTimerId = ( long ) pvTimerGetTimerID( pxTimer );
if (lTimerId != TIMER_ID) {
xil_printf("FreeRTOS Hello World Example FAILED");
}
if (RxtaskCntr >= TIMER_CHECK_THRESHOLD) {
xil_printf("FreeRTOS Hello World Example PASSED");
}
else {
xil_printf("FreeRTOS Hello World Example FAILED");
}
vTaskDelete( xRxTask );
vTaskDelete( xTxTask );
}
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