I'm trying to setup a 20Hz interrupt for Timer 2:
#define number_of_ms 50
void timer_config(void) {
NRF_TIMER2->TASKS_STOP = 1; // Stop timer
NRF_TIMER2->MODE = TIMER_MODE_MODE_Timer; // taken from Nordic dev zone
NRF_TIMER2->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
NRF_TIMER2->PRESCALER = 9; // 32us resolution
NRF_TIMER2->TASKS_CLEAR = 1; // Clear timer
// With 32 us ticks, we need to multiply by 31.25 to get milliseconds
NRF_TIMER2->CC[0] = number_of_ms * 31;
NRF_TIMER2->CC[0] += number_of_ms / 4;
NRF_TIMER2->INTENSET = TIMER_INTENSET_COMPARE0_Enabled
<< TIMER_INTENSET_COMPARE0_Pos;
NRF_TIMER2->SHORTS = (TIMER_SHORTS_COMPARE0_CLEAR_Enabled
<< TIMER_SHORTS_COMPARE0_CLEAR_Pos) &
TIMER_SHORTS_COMPARE0_CLEAR_Msk;
attachInterrupt(TIMER2_IRQn, TIMER2_Interrupt);
NRF_TIMER2->TASKS_START = 1; // Start TIMER
}
However no matter how I changed number_of_ms, the sampling frequency does not seem to change and seem to be 8Hz. I even changed the prescaler to 10!!
124767540, 2621, 103
124767540, 2621, 102
124767540, 2621, 100
124767540, 2621, 102
124767540, 2623, 100
124767540, 2618, 102
124767540, 2621, 103
124767541, 2622, 98
124767541, 2628, 99
124767541, 2619, 99
124767541, 2620, 101
124767541, 2622, 103
124767541, 2619, 104
124767541, 2621, 99
124767541, 2623, 97
124767542, 2622, 98
124767542, 2625, 98
124767542, 2620, 100
124767542, 2620, 99
124767542, 2621, 101
124767542, 2619, 102
124767542, 2620, 100
If I used millisecond resolution time, then the interrupt handler is fired up every 114ms, which is 8.77Hz.
163063, 2860, 82
163177, 2863, 82
163291, 2863, 84
163459, 2865, 83
163573, 2862, 81
163687, 2858, 82
163854, 2860, 82
163968, 2857, 82
164082, 2859, 81
164250, 2860, 81
164364, 2864, 82
164478, 2861, 82
164646, 2862, 82
164763, 2863, 82
164877, 2860, 82
165042, 2864, 82
165156, 2858, 83
165270, 2861, 82
165438, 2862, 81
165552, 2860, 82
165666, 2862, 83
How could this problem be solved?
UPDATE:
This is the code that write to SD card:
void loop() {
// Reading data from sensors to a buffer
if (readSensorFlag) {
readSensorFlag = false;
heartBeatReadFlag = true;
if (bufferCounter < BUFLEN - SAMPLESIZEINCHAR + 1) {
epoch = now();
proximity = vcnl.readProximity();
ambientLight = vcnl.readAmbient();
// format to be fixed length as opposed to variable length
// sacrifice overhead in written data with simpler and more robust code
// since we know exactly how much to increment after each write
int written = snprintf(&buffer[inBuf][bufferCounter], SAMPLESIZEINCHAR,
"%10lu,%5d,%5d\n",
epoch, proximity, ambientLight);
if (written > 0) {
bufferCounter += written;
}
} else {
// only switch buffer if out buffer is written to SD card
if (!outBufHasData) {
inBuf = inBuf? 0:1;
bufferCounter = 0;
outBufHasData = true;
}
}
}
