/* ppm_tick_acq: inline function called from the timer/counter1 interrupt
* service routine to handle adc sample acquisition and transmission.
*/
inline void ppm_tick_acq (void) {
/* declare a variable to store the read ADC sample. */
uint16_t adc = 0;
/* sample the ADC. */
adc = spi_read_adc ();
/* transmit the ADC sample to the usb host. */
usb_cdc_putchar (MSB (adc));
usb_cdc_putchar (LSB (adc));
/* increment the acquisition tick counter. */
ppm_acquire_ticks++;
}
/*=========================================================
Name: read_temp
Description:
This thread reads temperature from the thermistor through
the ADC. It converts the ADC counts to temperature and
calculates the PWM duty demand for the fan.
*=========================================================*/
void * read_temp(void * arg)
{
unsigned short int thermistor_counts; /* ADC value in counts */
unsigned short int thermistor_counts_prev; /* Previous value of ADC counts */
float temp_adc_v; /* ADC value in volts */
float temp; /* Temperature read by the thermistor */
float temp_ramp = 0.0f; /* Temperature ramped output */
static float prev_temp_ramp; /* Previous value of temperature ramped output */
static float pwm_temp = 0.0f; /* Value of temperature when PWM was updated */
unsigned char index = 0u;
static unsigned char first_run = TRUE; /* Flag to indicate first execution */
unsigned char print = FALSE; /* Display temperature */
/* Run indefinitely */
while(1)
{
/* Transmit ADC read command and receive results */
thermistor_counts = spi_read_adc(0);
/* Ignore small change in counts */
if (abs(thermistor_counts_prev -
thermistor_counts) < ADC_DIFFERENCE)
{
thermistor_counts = thermistor_counts_prev;
}
/* Convert counts to volts */
temp_adc_v = thermistor_counts * ADC_SCALING;
/* Convert volts to temperature */
temp = get_temperature(temp_adc_v);
/* First run */
if (TRUE == first_run)
{
first_run = FALSE;
/* No need to ramp for the first time */
temp_ramp = temp;
print = TRUE;
}
/* Look for temperature change and ramp slowly */
if (calc_diff(temp_ramp, temp) > 0.75)
{
temp_ramp = ramp_temperature(temp_ramp, temp);
print = TRUE;
}
/* Display temperature */
if (TRUE == print)
{
print = FALSE;
system("date");
fprintf (stdout, "Temperature is: %4.2f degC\n", temp_ramp);
/* Limit fan speed */
if ((temp_ramp/3) < 0)
{
index = 0;
}
else if ((temp_ramp/3) > 10)
{
index = 10;
}
else
{
index = (temp_ramp/3);
}
/* Update PWM demand for temperature change more than 2 degrees */
if (fabsf(temp_ramp - pwm_temp) >= 2.0)
{
pwm_temp = temp_ramp;
pwm_demand = fan_speed_dc[index - 1];
fprintf(stdout, "pwm demand %d%\n", pwm_demand);
}
}
/* Wait before next read */
sleep(1);
/* Store previous temperature value */
prev_temp_ramp = temp_ramp;
thermistor_counts_prev = thermistor_counts;
}
}