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