Simple example of FreeRTOS on Arduino

[Nicolas JAN]

Hi,

I work on a project which need some tasks carried out in the same time on
my Arduino Uno. And after few web researches, I found your project.

I try to make a simple example with a task which writes on the serial port.
But when I load the program, the arduino card sends me texts with strange
characters (example : GCÿƒ#ÿØ#ü¿cÿ€¤äƒ›ç¼ƒã£Dà [Ã'§'ä['¼¸C#$Dà)

Have you an idea where comes from this bug ?

This is my code :

main.c :

include <stdlib.h></stdlib.h>

include <stdbool.h></stdbool.h>

include <string.h></string.h>

#include <avr io.h=""></avr>

/ Scheduler include files. /

include <freertos.h></freertos.h>

include <task.h></task.h>

include <queue.h></queue.h>

include <semphr.h></semphr.h>

/ serial interface include file. /

include <lib_serial.h></lib_serial.h>

/ Create a handle for the serial port. /

xComPortHandle xSerialPort;

static void vHelloWorld(void*);

static void vHelloWorld(void*)

{

for( ;; )

{

xSerialPrintf("Hello World !\n");

vTaskDelay(1000);

}

}

/ Main program loop /

int16_t main(void) attribute((OS_main));

int16_t main(void)

{

xSerialPort = xSerialPortInitMinimal( 115200, portSERIAL_BUFFER,
portSERIAL_BUFFER);

avrSerialPrintf("Start of Main()\n");

xTaskCreate( vHelloWorld, ( signed portCHAR * ) "vHelloWorld", 50,
NULL,tskIDLE_PRIORITY+2, NULL );

vTaskStartScheduler();

}

--
Nicolas JAN

[Phillip Stevens]

Nicolas,

thanks for writing.

Garbage on the serial port is almost always caused by a mismatch of speeds. The Arduino frequency of 16MHz is one of the worst cases, because it doesn't divide closely to any serial bit rate and there's always a small rate error.

I'm guessing that this case is caused because the CPU_CLOCK_HZ is not set to 16000000. This is done in the freeRTOS/include/FreeRTOSConfig.h file. Just adjust the comment appropriately, from my default below.

    #define configCPU_CLOCK_HZ      ( ( uint32_t ) 22118400 )       // Modded Arduino (usually 16000000) with 328p device
//  #define configCPU_CLOCK_HZ      ( ( uint32_t ) 16000000 )       // Arduino with 328p device

For a bit more background, see here.
http://feilipu.posterous.com/freetronics-2010-arduino-overclocking-and-rev

Good luck.