The NTC thermistor sensor in drivers/sensor/ntc_thermistor/ntc_thermistor.c
cannot work with a 16-bit ADC.
The voltage becomes negative if the ADC raw value is 0x8000 or higher.
To correct this, I changed the types in the
ntc_thermistor_data struct from int16_t to int32_t.
This also corrects a potential problem at line 53
where we transform an int16_t into an int32_t.
Fixes: #75203
Signed-off-by: Robin Carrupt <robincarrupt@gmail.com>
bsearch() tries to find the exact match for the key, otherwise it
returns NULL. However, here we want to find two elements our key lies
in-between. This requires some rather complicated logic that pretends
it found the exact match even if it didn't. Replace this with a simple
implementation of binary search.
Signed-off-by: Paweł Anikiel <pan@semihalf.com>
The value of n_comp is wrong for ntc-thermistor-generic. Introduce a
helper macro to compute n_comp correctly for both thermistor types.
Signed-off-by: Paweł Anikiel <pan@semihalf.com>
The pullup resistance was assumed to be the maximum ADC value. This is
incorrect when the reference ADC voltage and the thermistor pullup
voltage differ. Use the pullup_uv property from DT instead.
The equations for the thermistor resistance are also wrong. The correct
equations are (see https://en.wikipedia.org/wiki/Voltage_divider):
R1 = R2 * (Vin / Vout - 1)
for the positive-connected resistor, and
R2 = R1 * (Vin / Vout - 1)^-1
for the negative-connected resistor. These were transformed so that
they can be computed using integer math.
Signed-off-by: Paweł Anikiel <pan@semihalf.com>
LOG_INF() inside of a sample_fetch create noise in the logs and is
inconsistent with other sensor driver implementations.
Signed-off-by: Maxmillion McLaughlin <github@maxmclau.com>
Add support for a generic NTC, `ntc-thermistor-generic`. In this case,
the compensation table is provided via devicetree. Note that DT property
is prefixed with `zephyr,`, because while hardware related, it is linked
to a particular software implementation.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
Refactor driver to align a bit more with its Linux counterpart, ie,
ntc_thermistor. This driver did quite a few _unconventional_ things,
like using "zephyr," compatibles, a dedicated node for pre-computed
compensation table (referenced by the actual pseudo-device node), etc.
The comparison helper function should likely be simplified as well (to
avoid the need for custom wrapper for bsearch), but this can be done
later.
In this refactor, each thermistor gets a compatible, e.g. "epcos,xxxx".
Compatibles are known by the driver, so are compensation tables. This
simplifies devicetree files. There's no need to bother about
compensation tables in **every** board file if Zephyr supports a certain
NTC model.
In general we should respect Linux bindings, which in the end influence
how drivers are implemented. In this case, this principle resulted in
simplified, easier to use code.
For future developers, this is how support for a new NTC can be added:
1. Add to the end of the driver:
```c
#undef DT_DRV_COMPAT
#define DT_DRV_COMPAT vnd_model
static __unused const struct ntc_compensation comp_vnd_model[] = {
{ x, y },
...,
};
#define DT_INST_FOREACH_STATUS_OKAY_VARGS(NTC_THERMISTOR_DEV_INIT,
DT_DRV_COMPAT, comp_vnd_model)
```
3. In driver's Kconfig make sure it depends on
DT_HAS_$DT_DRV_COMPAT$_ENABLED
Note: $X$ means _value_ of X.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
