drivers/ads1x1x: fix saul read adc

Author: baptleduc

drivers/ads1x1x/ads1x1x.c

@@ -289,9 +289,10 @@ int ads1x1x_read_raw(const ads1x1x_t *dev, int16_t *raw)
     return ADS1X1X_OK;
 }
 
-int ads1x1x_convert_to_mv(ads1x1x_t *dev, int16_t raw)
+int ads1x1x_convert_to_mv(const ads1x1x_t *dev, int16_t raw)
 {
     assert(dev);
+    /* Normalize signed ADC code: range = [-2^(N-1), 2^(N-1)-1] */
     return ((int32_t)raw * _ads1x1x_get_pga_voltage(dev->params.pga))
            / (1 << (ADS1X1X_BITS_RES - 1));
 }

drivers/ads1x1x/ads1x1x_saul.c

@@ -29,15 +29,12 @@ static int read_adc(const void *dev, phydat_t *res)
     const ads1x1x_t *mydev = dev;
 
     /* Read raw value */
-    if (ads1x1x_read_raw(mydev, res->val) < 0) {
+    int16_t raw;
+    if (ads1x1x_read_raw(mydev, &raw) < 0) {
         return ECANCELED;
     }
 
-    /* Convert raw ADC value to voltage according to PGA */
-    int32_t fsr_mv = _ads1x1x_get_pga_voltage(mydev->params.mux & ADS1X1X_PGA_MASK);
-    /* ADS101X_BITS_RES is 12 for ADS101x, 16 for ADS111x */
-    *res->val = (int16_t)(((int32_t)*(res->val) * fsr_mv) / (1 << (ADS1X1X_BITS_RES - 1)));
-
+    *res->val = (int16_t)(ads1x1x_convert_to_mv(mydev, raw));
     res->unit = UNIT_V;
     /* 1V = 1*10^3 mV */
     res->scale = -3;

drivers/ads1x1x/include/ads1x1x_internal.h

@@ -167,7 +167,7 @@ extern "C" {
  *
  * @return Voltage reference in millivolts
  */
-static inline int _ads1x1x_get_pga_voltage(uint8_t pga)
+static inline uint16_t _ads1x1x_get_pga_voltage(uint8_t pga)
 {
     switch (pga) {
     case ADS1X1X_PGA_FSR_6V144: return 6144;

drivers/include/ads1x1x.h

@@ -184,7 +184,7 @@ int ads1x1x_set_alert_parameters(ads1x1x_alert_t *dev, const ads1x1x_alert_param
  *
  * @return Converted value in millivolts
  */
-int ads1x1x_convert_to_mv(ads1x1x_t *dev, int16_t value);
+int ads1x1x_convert_to_mv(const ads1x1x_t *dev, int16_t value);
 
 /**
  * Reset the ADS1X1X devices on the I2C bus