Messages in this thread | | | Date | Thu, 05 Nov 2020 01:27:51 +0100 | From | Artur Rojek <> | Subject | Re: [PATCH] iio/adc: ingenic: Fix battery VREF for JZ4770 SoC |
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On 2020-11-05 01:09, Paul Cercueil wrote: > Hi Artur, > > Le mer. 4 nov. 2020 à 23:29, Artur Rojek <contact@artur-rojek.eu> a > écrit : >> Hi Paul, >> >> On 2020-11-04 20:28, Paul Cercueil wrote: >>> The reference voltage for the battery is clearly marked as 1.2V in >>> the >>> programming manual. With this fixed, the battery channel now returns >>> correct values. >>> >>> Fixes: a515d6488505 ("IIO: Ingenic JZ47xx: Add support for JZ4770 SoC >>> ADC.") >>> Cc: <stable@vger.kernel.org> >>> Signed-off-by: Paul Cercueil <paul@crapouillou.net> >>> --- >>> drivers/iio/adc/ingenic-adc.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/iio/adc/ingenic-adc.c >>> b/drivers/iio/adc/ingenic-adc.c >>> index ecaff6a9b716..19b95905a45c 100644 >>> --- a/drivers/iio/adc/ingenic-adc.c >>> +++ b/drivers/iio/adc/ingenic-adc.c >>> @@ -71,7 +71,7 @@ >>> #define JZ4725B_ADC_BATTERY_HIGH_VREF_BITS 10 >>> #define JZ4740_ADC_BATTERY_HIGH_VREF (7500 * 0.986) >>> #define JZ4740_ADC_BATTERY_HIGH_VREF_BITS 12 >>> -#define JZ4770_ADC_BATTERY_VREF 6600 >>> +#define JZ4770_ADC_BATTERY_VREF 1200 >>> #define JZ4770_ADC_BATTERY_VREF_BITS 12 >>> >>> #define JZ_ADC_IRQ_AUX BIT(0) >> >> I thought we set it to 6600 because GCW Zero was not showing correct >> battery values at 1200. >> But if you verified that 1200 works with JZ4770, then: >> Acked-by: Artur Rojek <contact@artur-rojek.eu> > > Yes, IIRC we were trying to figure out the range and settled with > [-3.3V,+3.3V] since it would give "plausible" values but which were > never quite right. The doc does say that the voltage is (hw_val / > 4096) * 1.2V, but also says that the ADC operated with 3.3V power > supply, I guess we got confused. We never considered the battery could > not be connected directly to the ADC's VBAT pin, so a 1.2V reference > didn't make sense at that time. I guess we need to learn about > electronics :) Yes we do :) > > It turns out the battery is connected to the VBAT pin with a 1 MOhm > resistor, and the VBAT pin is also pulled low with a 332 kOhm > resistor. So a fully charged battery with 4.2V reads as (4.2V * > 332000) / (1332000) = 1.05V, which totally fits in a [0V,+1.2V] range. > > With that same 4.2V battery I get a hardware value of about 3584, and > (3584 / 4096) * 1.2V == 1.05V, which matches the value computed above. > So the battery reading looks accurate this time. Excellent! Thanks for the detailed explanation.
Cheers, Artur > > Cheers, > -Paul
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