2.7.1 Code Example
Below is a code example showing the configuration of the ADC as an event
generator and an event user:
- Event user: ADC conversion triggered by
RTC overflow event
- RTC is configured to generate an RTC overflow event at the desired ADC sampling rate. The sampling rate in the example is 100 Hz.
- ADC conversion is triggered at a rate of 100 Hz and the result is read when the Result Ready (RESRDY) bit in the Interrupt Flags (ADCn.INTFLAGS) register is set.
- Event generator: Pin PB2 outputs an event (Pulse) when the ADC result is ready
#define F_CPU 3333333ul #include <avr/io.h> #include <math.h> #define TIMEBASE_VALUE ((uint8_t) ceil(F_CPU*0.000001)) #define ADC_MAX_VALUE (((1 << 12) / 2) - 1) /* In differential mode, the max value is 2047 */ /* Defines to easily configure RTC event frequency */ #define ADC_SAMPLING_FREQ 100 /* Hz */ #define RTC_CLOCK 32768 /* Hz */ #define RTC_PERIOD (RTC_CLOCK / ADC_SAMPLING_FREQ) /* Volatile variables to improve debug experience */ static volatile int32_t adc_reading; static volatile float voltage; /****************************************************************************** EVSYS initialization: Channel 0: Event system generator: RTC Overflow Event system user: ADC0 Channel 1: Event system generator: ADC0 Result Ready Event system user: EVOUTB (PIN PB2) *******************************************************************************/ void event_system_init(void) { PORTB.DIRSET = PIN2_bm; /* Configure EVOUTB to output */ EVSYS.CHANNEL0 = EVSYS_CHANNEL0_RTC_OVF_gc; /* RTC Overflow -> Channel 0 */ EVSYS.USERADC0START = EVSYS_USER_CHANNEL0_gc; /* Channel 0 -> ADC0 Start */ EVSYS.CHANNEL1 = EVSYS_CHANNEL1_ADC0_RES_gc; /* ADC RESRDY -> Channel 1 */ EVSYS.USEREVSYSEVOUTB = EVSYS_USER_CHANNEL1_gc; /* Channel 1 -> EVOUTB (PB2) */ } /********************************************************************************* RTC initialization **********************************************************************************/ void rtc_init(void) { while(RTC.STATUS > 0); /* Wait for all registers to be synchronized */ RTC.CTRLA = RTC_PRESCALER_DIV1_gc | RTC_RTCEN_bm; /* Enable RTC, no prescaler */ RTC.CLKSEL = RTC_CLKSEL_INT32K_gc; /* Select 32.768 kHz internal RC oscillator */ RTC.PER = RTC_PERIOD; while(RTC.STATUS > 0); /* Wait for all registers to be synchronized */ } /********************************************************************************** ADC initialization **********************************************************************************/ void adc_init() { ADC0.CTRLA = ADC_ENABLE_bm; ADC0.CTRLB = ADC_PRESC_DIV2_gc; /* fCLK_ADC = 3.333333/2 MHz */ ADC0.CTRLC = ADC_REFSEL_VDD_gc | (TIMEBASE_VALUE << ADC_TIMEBASE_gp); ADC0.CTRLE = 17; /* (SAMPDUR + 0.5) * fCLK_ADC = 10.5 µs sample duration */ ADC0.MUXPOS = ADC_MUXPOS_AIN6_gc; /* ADC channel AIN6 -> PA6 */ ADC0.MUXNEG = ADC_MUXNEG_AIN7_gc; /* ADC channel AIN7 -> PA7 */ /* Start ADC conversion on event trigger */ ADC0.COMMAND = ADC_DIFF_bm | ADC_MODE_SINGLE_12BIT_gc | ADC_START_EVENT_TRIGGER_gc; } int main(void) { event_system_init(); rtc_init(); adc_init(); while(1) { if(ADC0.INTFLAGS & ADC_RESRDY_bm) /* Check if ADC sample is ready */ { adc_reading = ADC0.RESULT; /* Read ADC result, clears the interrupt flag */ /* Calculate voltage on ADC pin, VDD = 3.3V, 12-bit resolution */ voltage = (float)((adc_reading * 3.3) / ADC_MAX_VALUE); } } }