On 02/12/2024 10:22, Matti Vaittinen wrote:
Hi Jonathan & Mikael,
On 01/12/2024 15:20, Jonathan Cameron wrote:
+};
+MODULE_DEVICE_TABLE(of, apds9160_of_match);
+
+static struct i2c_driver apds9160_driver = {
+ .driver = {
+ .name = APDS9160_DRIVER_NAME,
+ .owner = THIS_MODULE,
+ .of_match_table = apds9160_of_match,
+ },
+ .probe = apds9160_probe,
+ .remove = apds9160_remove,
+ .id_table = apds9160_id,
+};
First, regarding the integration time/gain/scale parameters. I took a
look at the datasheet again as there is a table
provided to get lux/count (scale?) for the ALS sensor depending on
gain and integration time.
It looks like the correlation in the table is almost linear but it's
not as there is a loss of precision.
For example, at 1x gain with integration time 100ms the lux/count is
0.819 but at 3x the table is stating 0.269 instead of exepected 0.273.
Is it still possible to use the gts helpers in that case?
Ah. Probably not if it goes non linear. Matti? (+CC)
Disclaimer - I didn't go through the patch and I just respond from the
top of my head :) So, please take my words with a pinch of salt.
AFAIR, it is not required that the impact of integration time is
_linear_ through the range. The "multiplication factor" can be set for
each integration time separately. So, it is perfectly Ok to say:
time 1 => multiply by 1
time 2 => multiply by 2
time 10 => multiply by 9 <= not linear, as linear would be 10.
time 15 => multiply by 15
...
The notable limitation of _current_ implementation is that the
"multiplication factor" needs to be integer. So, this may result loss of
accuracy.
// Snip.
I ended up re-reading this mail as a result of running some of my
public-inbox scripts...
...and I noticed that the non linear correlation was not about
integration time, but about gain. Eg, if I now read you right, the
integration time is kept constant 100mS, and gain is changed from 1x =>
3x, which actually did not bring 3x gain to the lux/count values.
If this is the case, then the GTS helpers aren't likely to help you
much. Sorry.
Yours,
-- Matti
