On 09/15/2012 01:15 AM, Kim, Milo wrote: >>> The LP8788 has 13 ADC input selection. >>> >>> ADC selection: >>> Battery voltage, general ADC1 and so on. >>> >>> ADC result: >>> Result = MAX_VALUE * (raw + 0.5) / 4095 except ADC is the charger >> voltage >>> If the ADC input is the charger voltage, >>> Result = MAX_VALUE * (raw + 0.5) / (4095 * 0.48) >>> >>> The raw value is from the registers. >>> It has the range between 0 to 4095. (12bits) >>> >>> MAX_VALUE is constant for each selection. >>> For the battery voltage, there are three ADC inputs. 5.0/5.5/6.0V >>> Battery voltage for Max 5.0V = 5.0 >>> Battery voltage for Max 5.5V = 5.5 >>> Battery voltage for Max 6.0V = 6.0 >>> Charger = 6.0 >>> ADC1 = 2.5 >>> >>> I'm afraid I still misunderstand how IIO ADC works. >>> Could you me some guide how to setup the scale in the driver? >> >> The scale is a fixpoint value, which should be multiplied with the raw >> value >> to get the result in the proper unit. The unit depends on the channel >> type, >> e.g. for voltage it is mV and for temperature it is C. The number of >> decimal >> places for the fixed point value depends on whether you return >> INT_PLUS_MICRO it's 6, if you return INT_PLUS_NANO it is 9. The digits >> before the decimal point are stored in "val" the digits after the >> decimal >> point are stored in "val2". >> >> E.g. if you have >> *val = 1; >> *val2 = 1256; >> return INT_PLUS_MICRO; >> >> your scale factor is 1.001256, if you'd return INT_PLUS_NANO you scale >> factor would be 1.0000001256 instead. >> >> In your case you could for example calculate the voltage scales as: >> >> tmp = MAX_VALUE * 1000000 / 4095; >> *val = tmp / 1000000; >> *val2 = tmp % 1000000; >> >> This assumes that MAX_VALUE is in millivolt. >> >> E.g. if MAX_VALUE is 5.0V you should get a scale of 1.220703 (val = 1, >> val2 >> = 220703). Since your MAX_VALUE is fixed you can probably just pre- >> calculate >> the result of MAX_VALUE * 1000000 / 4095 for each channel, similar like >> you >> already did with your lp8788_scale table. > > Superb! Thanks a lot for your clear explanation. > > I have one more question about the temperature ADC. > > The LP8788 has no dedicated temperature ADC, but it provides four > general inputs - ADC1 to 4. > The IIO consumer can get the battery temperature among general ADC inputs. > I think the ADC driver should not assume that ADC1..4 is for the temperature, > because the selection is configurable in the platform side. > > Then how can I set the unit of ADC MAX_VALUE? > I would set the unit of ADC MAX_VALUE to mili (same as voltage) and > the result is converted by the IIO consumer manually. > Does it make sense ? Yes, if there is a temperature sensor attached to an ADC channel it is not up to the ADC driver to know this, but rather to the consumer driver. > > Best Regards, > Milo > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
