Dear Lars,
On 07/03/2013 12:46 PM, Lars-Peter Clausen wrote:
The scale attribute reports the scale of the raw value. To gain the value of
the result in mV you have to multiply the raw attribute with the scale
attribute. The scale attribute does not return the result of a conversion with
a scale different applied.
Thank you for the guidance, I misunderstood the whole thing.
I suggest you implement this in two steps. First implement the scale property
for all channels. Use a LUT for each channel's fullscale value (in mV) and
implement reading the scale like this.
case IIO_CHAN_INFO_SCALE:
*val = lut[chan->channel];
*val2 = chan->scan_type.realbits;
return IIO_VAL_FRACTIONAL_LOG2;
The next step is to make the scale modifiable for channels which support this.
I'm sorry, it's the first time I work with an iio driver and I'm afraid I don't
understand this.
Let's say the fullscale value for channel 0 is 1.85V by default (when divide_by_two is
disabled) and 3.7V (when enabled).
The channel's realbits is currently set to 18, because (although the ADC resolution is
12 bits) the device can read several samples and return an accumulated value in 18 bits.
Now, considering the default case where 1.85V is the max ref voltage and considering
that the driver only reads one sample during the raw_read operation (12 bits), what
value should a read of 'scale' return?
scale = Vref_mv / ((1 << 12) - 1) = 1850 /4095 = 0.45177045 ?
That is, the value to multiply the raw value to get the voltage in mV?
So that if reading the 'raw' returns say 425 and reading scale returns 0.45177 the
measured voltage is 425 * 0.45177 = 192mV?
Then let's say I have implemented a function to modify the scale (which should
eventually allow me to enable/disable the by two divisor). What is the user supposed
to write to the 'scale'? Is he supposed to supply a decimal number like 0.45177 * 2 =
0.903? This would be pretty odd.
Should I create a table instead so that writing a 0 means divisor disabled and writing
1 means divisor enabled, for example?
Does the iio provide any descriptor that automatically shows the value in mV (already
converted)?
Thank you for your help.
Best regards,
--
Hector Palacios
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