application: add ADC to measure target voltage

application.c

@@ -24,6 +24,7 @@
 #include <libopencm3/stm32/dbgmcu.h> // debug utilities
 #include <libopencm3/stm32/desig.h> // design utilities
 #include <libopencm3/stm32/flash.h> // flash utilities
+#include <libopencm3/stm32/adc.h> // ADC utilities
 
 /* own libraries */
 #include "global.h" // board definitions
@@ -49,6 +50,10 @@ static volatile bool second_flag = false; /**< flag set when a second passed */
 /** number of seconds since boot */
 static uint32_t boot_time = 0;
 
+#define TARGET_CHANNEL 6 /**< PA6/ADC1_IN6 used to measure target voltage */
+#define SIGNAL_CHANNEL 1 /**< PA1/ADC1_IN1 used to measure signal voltage */
+const uint8_t adc_channels[] = {ADC_CHANNEL17, ADC_CHANNEL(TARGET_CHANNEL), ADC_CHANNEL(SIGNAL_CHANNEL)}; /**< voltages to convert (channel 17 = internal voltage reference) */
+
 size_t putc(char c)
 {
 	size_t length = 0; // number of characters printed
@@ -65,6 +70,26 @@ size_t putc(char c)
 	return length; // return number of characters printed
 }
 
+/** measure target and signal voltages
+ *  @return voltages of channels
+ */
+static float* measure_voltages(void)
+{
+	static float voltages[LENGTH(adc_channels)]; // to store and return the voltages
+
+	// read lid temperature using ADC
+	ADC_SR(ADC1) = 0; // reset flags
+	uint16_t adc_values[LENGTH(adc_channels)];
+	for (uint8_t i = 0; i < LENGTH(adc_channels); i++) {
+		adc_start_conversion_regular(ADC1); // start conversion (using trigger)
+		while (!adc_eoc(ADC1)); // wait until conversion finished
+		adc_values[i] = adc_read_regular(ADC1); // read voltage value (clears flag)
+		voltages[i] = adc_values[i] * 1.21 / adc_values[0]; // use 1.21 V internal voltage reference to get ADC voltage
+	}
+	voltages[1] *= 2.0; // the is a /2 voltage divider for target voltage
+	return voltages;
+}
+
 // menu commands
 
 /** display available commands
@@ -440,6 +465,26 @@ void main(void)
 	// important: do not re-enable backup_domain_write_protect, since this will prevent clearing flags (but RTC registers do not need to be unlocked)
 	puts("OK\n");
 
+	puts("setup ADC to measure voltages: ");
+	rcc_periph_clock_enable(RCC_ADC1); // enable clock for ADC domain
+	adc_power_off(ADC1); // switch off ADC while configuring it
+	adc_set_right_aligned(ADC1); // ensure it is right aligned to get the actual value in the 16-bit register
+	adc_enable_scan_mode(ADC1); // use scan mode do be able to go to next discontinuous subgroup of the regular sequence
+	adc_enable_discontinuous_mode_regular(ADC1, 1); // use discontinuous mode (to go through all channels of the group, one after another)
+	adc_set_single_conversion_mode(ADC1); // ensure continuous mode is not used (that's not the same as discontinuous)
+	adc_eoc_after_each(ADC1); // set EOC after each conversion instead of each group
+	adc_set_sample_time_on_all_channels(ADC1, ADC_SMPR_SMP_28CYC); // use at least 15 cycles to be able to sample at 12-bit resolution
+	adc_set_regular_sequence(ADC1, LENGTH(adc_channels), (uint8_t*)adc_channels); // set channel to convert
+	adc_enable_temperature_sensor(); // enable internal voltage reference
+	adc_power_on(ADC1); // switch on ADC
+	sleep_us(3); // wait t_stab for the ADC to stabilize
+	rcc_periph_clock_enable(RCC_ADC1_IN(TARGET_CHANNEL)); // enable clock for GPIO domain for target voltage channel
+	gpio_mode_setup(ADC1_IN_PORT(TARGET_CHANNEL), GPIO_MODE_ANALOG, GPIO_PUPD_NONE, ADC1_IN_PIN(TARGET_CHANNEL)); // set target voltage channel as analog input for the ADC
+	rcc_periph_clock_enable(RCC_ADC1_IN(SIGNAL_CHANNEL)); // enable clock for GPIO domain for signal channel
+	gpio_mode_setup(ADC1_IN_PORT(SIGNAL_CHANNEL), GPIO_MODE_ANALOG, GPIO_PUPD_NONE, ADC1_IN_PIN(SIGNAL_CHANNEL)); // set signal channel as analog input for the ADC
+	measure_voltages(); // try to measure voltages
+	puts("OK\n");
+
 	// setup terminal
 	terminal_prefix = ""; // set default prefix
 	terminal_process = &process_command; // set central function to process commands