swlink: Measure voltage on VDD pin of Stlink/Stm8s.

src/platforms/swlink/platform.c

@@ -39,6 +39,8 @@ uint32_t led_error_port;
 uint16_t led_error_pin;
 static uint8_t rev;
 
+static void adc_init(void);
+
 int platform_hwversion(void)
 {
 	return rev;
@@ -80,6 +82,7 @@ void platform_init(void)
 		/* LED GPIO already set in detect_rev()*/
 		led_error_port = GPIOA;
 		led_error_pin = GPIO8;
+		adc_init();
 		break;
 	case 1:
 		led_error_port = GPIOC;
@@ -137,9 +140,47 @@ bool platform_srst_get_val(void)
 	return gpio_get(JRST_PORT, JRST_PIN) == 0;
 }
 
+static void adc_init(void)
+{
+	rcc_periph_clock_enable(RCC_ADC1);
+	/* PA0 measures CN7 Pin 1 VDD divided by two.*/
+	gpio_set_mode(GPIOA, GPIO_MODE_INPUT,
+				  GPIO_CNF_INPUT_ANALOG, GPIO0);
+	adc_power_off(ADC1);
+	adc_disable_scan_mode(ADC1);
+	adc_set_single_conversion_mode(ADC1);
+	adc_disable_external_trigger_regular(ADC1);
+	adc_set_right_aligned(ADC1);
+	adc_set_sample_time_on_all_channels(ADC1, ADC_SMPR_SMP_28DOT5CYC);
+
+	adc_power_on(ADC1);
+
+	/* Wait for ADC starting up. */
+	for (int i = 0; i < 800000; i++)	/* Wait a bit. */
+		__asm__("nop");
+
+	adc_reset_calibration(ADC1);
+	adc_calibrate(ADC1);
+}
+
 const char *platform_target_voltage(void)
 {
-	return "unknown";
+	static char ret[] = "0.0V";
+	const uint8_t channel = 0;
+	switch (rev) {
+	case 0:
+		adc_set_regular_sequence(ADC1, 1, (uint8_t*)&channel);
+		adc_start_conversion_direct(ADC1);
+		/* Wait for end of conversion. */
+		while (!adc_eoc(ADC1));
+		/* Referencevoltage is 3.3 Volt, measured voltage is half of
+		 * actual voltag. */
+		uint32_t val_in_100mV = (adc_read_regular(ADC1) * 33 * 2) / 4096;
+		ret[0] = '0' + val_in_100mV / 10;
+		ret[2] = '0' + val_in_100mV % 10;
+		return ret;
+	}
+	return "ABSENT!";
 }
 
 void set_idle_state(int state)