Messages in this thread | | | Date | Thu, 05 Nov 2020 00:09:15 +0000 | From | Paul Cercueil <> | Subject | Re: [PATCH] iio/adc: ingenic: Fix battery VREF for JZ4770 SoC |
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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 :)
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.
Cheers, -Paul
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