Hi Artur,
Le mer. 4 nov. 2020 à 23:29, Artur Rojek <contact@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxxx>
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
