samples: adc_sequence: differential mode handling in ADC conversion

This commit updates the ADC sequence sample to improve handling of
differential mode readings. It modifies the conversion logic to
correctly interpret 16-bit/32-bit signed values and adjusts the
resolution accordingly. This ensures accurate millivolt conversion
for both differential and single-ended configurations.

Signed-off-by: Martin Hoff <[email protected]>

Author: Martinhoff-maker

samples/drivers/adc/adc_sequence/src/main.c

@@ -92,13 +92,30 @@ int main(void)
 			       CONFIG_SEQUENCE_SAMPLES);
 			for (size_t sample_index = 0U; sample_index < CONFIG_SEQUENCE_SAMPLES;
 			     sample_index++) {
-
-				val_mv = channel_reading[sample_index][channel_index];
-
+				uint8_t res = CONFIG_SEQUENCE_RESOLUTION;
+
+				/*
+				 * If using differential mode, the 16/32 bit value
+				 * in the ADC sample buffer should be a signed 2's
+				 * complement value.
+				 * Also reduce the resolution by 1 for the conversion
+				 */
+				if (channel_cfgs[channel_index].differential) {
+#ifdef CONFIG_SEQUENCE_32BITS_REGISTERS
+					val_mv = (int32_t)
+						channel_reading[sample_index][channel_index];
+#else
+					val_mv = (int32_t)((int16_t)channel_reading[sample_index]
+										   [channel_index]);
+#endif
+					res -= 1;
+				} else {
+					val_mv = channel_reading[sample_index][channel_index];
+				}
 				printf("- - %" PRId32, val_mv);
 				err = adc_raw_to_millivolts(vrefs_mv[channel_index],
 							    channel_cfgs[channel_index].gain,
-							    CONFIG_SEQUENCE_RESOLUTION, &val_mv);
+							    res, &val_mv);
 
 				/* conversion to mV may not be supported, skip if not */
 				if ((err < 0) || vrefs_mv[channel_index] == 0) {