mbed generate chirp singal - mbed

Question

I am using LPCXpresso1549 to generate chirp signal with frequency between 35000 Hz and 45000 Hz. First off, I generate DAC chirp samples on matlab, and store them in const uint16_t chirpData[]. The samples frequency is 96000 Hz, therefore 96001 samples. Then, I set the timer to send samples out one by one every (1/96000) second. However, my signal I got having frequency between 3200 Hz to 44000 Hz. Is that because the timer is slow?
enter code here
const uint16_t chirpData[NUM_SAMPLES] = { 2048, ...., 1728, 2048} //96001 sampels
#include "mbed.h"
#include "chirp.h"
Serial pc(USBTX, USBRX);
Timer t;
AnalogOut aout(P0_12);
int main()
{
int i = 0;
while(true) {
// Write the sample to the analog
t.start(); //start timer
if(t.read() >= 0.00001){ // 1/samplef = 0.00001
aout.write_u16(chirpData[i]);
i++;
t.reset(); // reset timer to zero
if(i > 96000) {
i = 0;
}
}
}
}

Answer 1

In this case I recommend you using Threads executing Tasks by:
#define xTaskCreate( pvTaskCode, pcName, usStackDepth, pvParameters, uxPriority, pxCreatedTask ) xTaskGenericCreate( ( pvTaskCode ), ( pcName ), ( usStackDepth ), ( pvParameters ), ( uxPriority ), ( pxCreatedTask ), ( NULL ), ( NULL ) )
xTaskHandle taskHandle;
xTaskCreate(..); //Check Task.h
Then you can set your task cycle by
void your_task() {
unsigned task_cycle_ms = 1/freq; //Careful, convert to ms.
portTickType xLastWakeTime = 0;
portTickType xFrequency = task_cycle_ms/portTICK_RATE_MS;
for(;;) {
vTaskDelayUntil( &xLastWakeTime, xFrequency );
//your code to execute every cycle here
}
}