Hi Nuno,
On 6/26/24 10:59, Nuno Sá wrote:
Hi Olivier,
One thing that I just noticed...
On Tue, 2024-06-25 at 17:07 +0200, Olivier Moysan wrote:
Add scaling support to STM32 DFSDM.
When used in an analog context, a DFSDM filter typically converts the data
from a sigma delta modulator. The IIO device associated to the DFSDM
filter provides these data as raw data.
The IIO device can provide scaling information (voltage and offset) to
allow conversion of raw data into physical values.
With the new binding based on IIO backend framework, the sigma delta
modulators are defined as backends providing scaling information.
The scaling is not supported with legacy binding.
Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxxxxxxx>
Acked-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
---
...
+
+ case IIO_CHAN_INFO_SCALE:
+ /*
+ * Scale is expressed in mV.
+ * When fast mode is disabled, actual resolution may be lower
+ * than 2^n, where n = realbits - 1.
+ * This leads to underestimating the input voltage.
+ * To compensate this deviation, the voltage reference can be
+ * corrected with a factor = realbits resolution / actual max
+ */
+ if (adc->backend[idx]) {
+ iio_backend_read_raw(adc->backend[idx], chan, val,
val2, mask);
Eve if it does not matter for your usecase, you should still do error handling
as iio_backend_read_raw() can return an error.
Ack. On the same occasion, I will switch to a dedicated API.
Olivier
+ *val = div_u64((u64)*val * (u64)BIT(DFSDM_DATA_RES -
1), max);
+ *val2 = chan->scan_type.realbits;
+ if (chan->differential)
+ *val *= 2;
+ }
+ return IIO_VAL_FRACTIONAL_LOG2;
+
+ case IIO_CHAN_INFO_OFFSET:
+ /*
+ * DFSDM output data are in the range [-2^n, 2^n],
+ * with n = realbits - 1.
+ * - Differential modulator:
+ * Offset correspond to SD modulator offset.
+ * - Single ended modulator:
+ * Input is in [0V, Vref] range,
+ * where 0V corresponds to -2^n, and Vref to 2^n.
+ * Add 2^n to offset. (i.e. middle of input range)
+ * offset = offset(sd) * vref / res(sd) * max / vref.
+ */
+ if (adc->backend[idx]) {
+ iio_backend_read_raw(adc->backend[idx], chan, val,
val2, mask);
Same...
- Nuno Sá
