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drivers: sensor: nxp_kinetis_temp: add weighted average filter

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Add an optional weighted average filter to the ADC readings in the NXP
Kinetis temperature sensor driver as recommended in NXP AN3031.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
This commit is contained in:
Henrik Brix Andersen 2020-03-20 14:17:17 +01:00 • committed by Maureen Helm
commit c8d26b4b14
2 changed files with 26 additions and 0 deletions
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6
drivers/sensor/nxp_kinetis_temp/Kconfig
View file

@ -28,4 +28,10 @@ config TEMP_KINETIS_OVERSAMPLING
bandgap voltage readings. Oversampling can help in providing
more stable readings.
config TEMP_KINETIS_FILTER
bool "Enable digital filtering of ADC readings"
help
Enable weighted average digital filtering of the ADC
readings as per NXP AN3031.
endif # TEMP_KINETIS

20
drivers/sensor/nxp_kinetis_temp/temp_kinetis.c
View file

@ -45,6 +45,10 @@ static int temp_kinetis_sample_fetch(struct device *dev,
{
const struct temp_kinetis_config *config = dev->config->config_info;
struct temp_kinetis_data *data = dev->driver_data;
#ifdef CONFIG_TEMP_KINETIS_FILTER
u16_t previous[TEMP_KINETIS_ADC_SAMPLES];
int i;
#endif /* CONFIG_TEMP_KINETIS_FILTER */
int err;
/* Always read both sensor and bandgap voltage in one go */
@ -53,6 +57,10 @@ static int temp_kinetis_sample_fetch(struct device *dev,
return -ENOTSUP;
}
#ifdef CONFIG_TEMP_KINETIS_FILTER
memcpy(previous, data->buffer, sizeof(previous));
#endif /* CONFIG_TEMP_KINETIS_FILTER */
err = adc_read(data->adc, &config->adc_seq);
if (err) {
LOG_ERR("failed to read ADC channels (err %d)", err);
@ -61,6 +69,18 @@ static int temp_kinetis_sample_fetch(struct device *dev,
LOG_DBG("sensor = %d, bandgap = %d", data->buffer[0], data->buffer[1]);
#ifdef CONFIG_TEMP_KINETIS_FILTER
if (previous[0] != 0 && previous[1] != 0) {
for (i = 0; i < ARRAY_SIZE(previous); i++) {
data->buffer[i] = (data->buffer[i] >> 1) +
(previous[i] >> 1);
}
LOG_DBG("sensor = %d, bandgap = %d (filtered)", data->buffer[0],
data->buffer[1]);
}
#endif /* CONFIG_TEMP_KINETIS_FILTER */
return 0;
}