laurelin/src/light_sensor.c

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C
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2020-07-11 21:04:07 +02:00
#include "light_sensor.h"
volatile unsigned int LightSensor_Measurement;
volatile bool LightSensor_NewMeasurement = false;
// Rolling average of the brightness measurement
float LightSensor_AbsoluteBrightness = 0.5f;
// Maximum and minimum encountered so far
float LightSensor_MinimumBrightness = 1.0f;
float LightSensor_MaximumBrightness = 0.0f;
float LightSensor_RelativeBrightness;
static void LightSensor_Measure(void)
{
// Use light sensor pin in output mode, drive high
GPIOB->MODER = (GPIOB->MODER & ~(0x03 << PIN_LIGHT_SENSOR * 2))
| (0x01 << PIN_LIGHT_SENSOR * 2);
// Disable timer
TIM14->SR = 0x0000;
TIM14->CR1 = 0x0000;
TIM14->CNT = 0;
// Delay a bit to ensure capacitor is charged
for(unsigned int i = 0; i < 100; i++)
{
__asm__ volatile("nop");
}
// Re-enable timer
TIM14->CR1 = TIM_CR1_CEN;
// Switch to alternate function mode
GPIOB->MODER = (GPIOB->MODER & ~(0x03 << PIN_LIGHT_SENSOR * 2))
| (0x02 << PIN_LIGHT_SENSOR * 2);
}
void LightSensor_Init(void)
{
RCC->AHBENR |= RCC_AHBENR_GPIOBEN;
RCC->APB1ENR |= RCC_APB1ENR_TIM14EN;
GPIOB->ODR |= (1 << PIN_LIGHT_SENSOR);
GPIOB->AFR[0] &= ~(0x0f << (PIN_LIGHT_SENSOR * 4));
// Enable input capture for light sensor pin, trigger on falling edge
TIM14->CCMR1 = TIM_CCMR1_CC1S_0;
TIM14->CCER = TIM_CCER_CC1E | TIM_CCER_CC1P;
// Set up TIM14 for an oveflow interrupt at the configured interval
TIM14->PSC = 48000 * LIGHTSENSOR_INTERVAL / 65535;
TIM14->ARR = 65535;
TIM14->DIER = TIM_DIER_UIE;
NVIC_EnableIRQ(TIM14_IRQn);
LightSensor_Measure();
}
void LightSensor_Poll(void)
{
if(LightSensor_NewMeasurement)
{
unsigned int measurement = LightSensor_Measurement;
LightSensor_NewMeasurement = false;
float brightness = 1.0f - measurement / 65535.0f;
if(measurement != 65535 && brightness < LightSensor_MinimumBrightness)
{
LightSensor_MinimumBrightness = brightness;
}
if(brightness > LightSensor_MaximumBrightness)
{
LightSensor_MaximumBrightness = brightness;
}
LightSensor_AbsoluteBrightness = LIGHTSENSOR_LAMBDA * LightSensor_AbsoluteBrightness
+ (1.0f - LIGHTSENSOR_LAMBDA) * brightness;
// Slowly move maximum and minimum back to 0.0 and 1.0, respectively
LightSensor_MaximumBrightness *= LIGHTSENSOR_ALPHA;
LightSensor_MinimumBrightness = 1.0f - LightSensor_MinimumBrightness;
LightSensor_MinimumBrightness *= LIGHTSENSOR_ALPHA;
LightSensor_MinimumBrightness = 1.0f - LightSensor_MinimumBrightness;
// Scale and saturate to get relative brightness value
float range = LightSensor_MaximumBrightness
- LightSensor_MinimumBrightness;
float low = LightSensor_MinimumBrightness
+ range * LIGHTSENSOR_LOW_BOUND;
float high = LightSensor_MinimumBrightness
+ range * LIGHTSENSOR_HIGH_BOUND;
LightSensor_RelativeBrightness = (LightSensor_AbsoluteBrightness - low)
/ (high - low);
if(LightSensor_RelativeBrightness < 0.0f)
{
LightSensor_RelativeBrightness = 0.0f;
}
if(LightSensor_RelativeBrightness > 1.0f)
{
LightSensor_RelativeBrightness = 1.0f;
}
}
}
void TIM14_IRQHandler(void)
{
if(TIM14->SR & TIM_SR_CC1IF)
{
LightSensor_Measurement = TIM14->CCR1;
}
else
{
LightSensor_Measurement = 65535;
}
LightSensor_NewMeasurement = true;
LightSensor_Measure();
}