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SubjectRe: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed
On Mon, 18 Dec 2017 10:02:44 +0100
Stefan Brüns <stefan.bruens@rwth-aachen.de> wrote:

> On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote:
> > Calibration register is used for calculating current register in
> > hardware according to datasheet:
> > current = shunt_volt * calib_register / 2048 (ina 226)
> > current = shunt_volt * calib_register / 4096 (ina 219)
> >
> > Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> > order to avoid truncation error and provide best precision allowed
> > by shunt_voltage measurement. Make current scale value follow changes
> > of shunt_resistor from sysfs as calib_register value is now fixed.
> >
> > Power_lsb value should also follow shunt_resistor changes as stated in
> > datasheet:
> > power_lsb = 25 * current_lsb (ina 226)
> > power_lsb = 20 * current_lsb (ina 219)
> >
> > This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394
> >
> > Signed-off-by: Maciej Purski <m.purski@samsung.com>
>
> Reviewed-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Applied to the togreg branch of iio.git and pushed out ass testing
for the autobuilders to play with it.

Thanks,

Jonathan
>
> > ---
> > Changes in v4:
> > - fix comments
> >
> > Changes in v3:
> > - remove variable current_lsb and calculate it on each read of current
> > and power scale value
> > - update comments
> >
> > Changes in v2:
> > - rebase on top of the latest next
> > - remove a redundant variable - power_lsb_uW
> > - fix comments
> > ---
> > drivers/iio/adc/ina2xx-adc.c | 64
> > +++++++++++++++++++++++--------------------- 1 file changed, 33
> > insertions(+), 31 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> > index ddf8781..9e8ca12 100644
> > --- a/drivers/iio/adc/ina2xx-adc.c
> > +++ b/drivers/iio/adc/ina2xx-adc.c
> > @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 };
> >
> > struct ina2xx_config {
> > u16 config_default;
> > - int calibration_factor;
> > + int calibration_value;
> > int shunt_voltage_lsb; /* nV */
> > int bus_voltage_shift; /* position of lsb */
> > int bus_voltage_lsb; /* uV */
> > - int power_lsb; /* uW */
> > + /* fixed relation between current and power lsb, uW/uA */
> > + int power_lsb_factor;
> > enum ina2xx_ids chip_id;
> > };
> >
> > @@ -149,20 +150,20 @@ struct ina2xx_chip_info {
> > static const struct ina2xx_config ina2xx_config[] = {
> > [ina219] = {
> > .config_default = INA219_CONFIG_DEFAULT,
> > - .calibration_factor = 40960000,
> > + .calibration_value = 4096,
> > .shunt_voltage_lsb = 10000,
> > .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT,
> > .bus_voltage_lsb = 4000,
> > - .power_lsb = 20000,
> > + .power_lsb_factor = 20,
> > .chip_id = ina219,
> > },
> > [ina226] = {
> > .config_default = INA226_CONFIG_DEFAULT,
> > - .calibration_factor = 5120000,
> > + .calibration_value = 2048,
> > .shunt_voltage_lsb = 2500,
> > .bus_voltage_shift = 0,
> > .bus_voltage_lsb = 1250,
> > - .power_lsb = 25000,
> > + .power_lsb_factor = 25,
> > .chip_id = ina226,
> > },
> > };
> > @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
> > *val2 = 1000;
> > return IIO_VAL_FRACTIONAL;
> >
> > - case INA2XX_POWER:
> > - /* processed (mW) = raw*lsb (uW) / 1000 */
> > - *val = chip->config->power_lsb;
> > - *val2 = 1000;
> > + case INA2XX_CURRENT:
> > + /*
> > + * processed (mA) = raw * current_lsb (mA)
> > + * current_lsb (mA) = shunt_voltage_lsb (nV) /
> > + * shunt_resistor (uOhm)
> > + */
> > + *val = chip->config->shunt_voltage_lsb;
> > + *val2 = chip->shunt_resistor_uohm;
> > return IIO_VAL_FRACTIONAL;
> >
> > - case INA2XX_CURRENT:
> > - /* processed (mA) = raw (mA) */
> > - *val = 1;
> > - return IIO_VAL_INT;
> > + case INA2XX_POWER:
> > + /*
> > + * processed (mW) = raw * power_lsb (mW)
> > + * power_lsb (mW) = power_lsb_factor (mW/mA) *
> > + * current_lsb (mA)
> > + */
> > + *val = chip->config->power_lsb_factor *
> > + chip->config->shunt_voltage_lsb;
> > + *val2 = chip->shunt_resistor_uohm;
> > + return IIO_VAL_FRACTIONAL;
> > }
> >
> > case IIO_CHAN_INFO_HARDWAREGAIN:
> > @@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(struct
> > device *dev, }
> >
> > /*
> > - * Set current LSB to 1mA, shunt is in uOhms
> > - * (equation 13 in datasheet). We hardcode a Current_LSB
> > - * of 1.0 x10-3. The only remaining parameter is RShunt.
> > - * There is no need to expose the CALIBRATION register
> > - * to the user for now. But we need to reset this register
> > - * if the user updates RShunt after driver init, e.g upon
> > - * reading an EEPROM/Probe-type value.
> > + * Calibration register is set to the best value, which eliminates
> > + * truncation errors on calculating current register in hardware.
> > + * According to datasheet (INA 226: eq. 3, INA219: eq. 4) the best values
> > + * are 2048 for ina226 and 4096 for ina219. They are hardcoded as
> > + * calibration_value.
> > */
> > static int ina2xx_set_calibration(struct ina2xx_chip_info *chip)
> > {
> > - u16 regval = DIV_ROUND_CLOSEST(chip->config->calibration_factor,
> > - chip->shunt_resistor_uohm);
> > -
> > - return regmap_write(chip->regmap, INA2XX_CALIBRATION, regval);
> > + return regmap_write(chip->regmap, INA2XX_CALIBRATION,
> > + chip->config->calibration_value);
> > }
> >
> > static int set_shunt_resistor(struct ina2xx_chip_info *chip, unsigned int
> > val) {
> > - if (val <= 0 || val > chip->config->calibration_factor)
> > + if (val == 0 || val > INT_MAX)
> > return -EINVAL;
> >
> > chip->shunt_resistor_uohm = val;
> > @@ -592,11 +599,6 @@ static ssize_t ina2xx_shunt_resistor_store(struct
> > device *dev, if (ret)
> > return ret;
> >
> > - /* Update the Calibration register */
> > - ret = ina2xx_set_calibration(chip);
> > - if (ret)
> > - return ret;
> > -
> > return len;
> > }
>
>

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