Accuracy of 1.8 volt reference on BBB?

What's the accuracy of the 1.8 volts VADC reference voltage on the
BBB? Or, more to the point, what's its stability? It's easy enough
to calibrate voltage measurements by using an accurate voltmeter to
measure the same voltage and then scaling the result appropriately in
software but if the 1.8 volts reference isn't reasonably stable then
one is wasting one's time.

Check the datasheet of the PMIC.

Gerald

Of course, thanks.

cl@isbd.net wrote:

External. Or internal. Or whichever one you want to use.

Gerald

So it's selectable by software? What does it default to using at
power on? I can't find any documentation about this in the BBB manual
and the processor manual is not much more forthcoming. The processor
manual told me that the ADC can use either internal or external
reference but I could find nothing further about it at all.

I have no idea what the SW defaults to. The BBB manual is basically the HW and nothing about the SW. You will need to dive into the code. The External voltage is 1.8V, which is the MAX voltage So I would expect that the internal reference is based off of that.

Gerald

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External. Or internal. Or whichever one you want to use.

So it's selectable by software? What does it default to using at
power on? I can't find any documentation about this in the BBB manual
and the processor manual is not much more forthcoming. The processor
manual told me that the ADC can use either internal or external
reference but I could find nothing further about it at all.

If you know the register name that is used to select between internal and
external ref, then use ³git grep <reg-name>² to find where that register
gets used in the kernel source. If there is no reference to this register,
then the default value will be used.

Regards,
John

That's the problem, I can't find any documentation anywhere that tells
me about the internal/external switching. The whole of the ADC system
is shrouded in mystery! :slight_smile:

  1. Go to http://www.ti.com/product/am3358

  2. Download the Technical Reference Manual

  3. Look under Section 12…Touchscreen Controller.

Gerald

>> [-- text/plain, encoding quoted-printable, charset: ISO-8859-1, 43
>>lines --]
>>
>> External. Or internal. Or whichever one you want to use.
>>
>So it's selectable by software? What does it default to using at
>power on? I can't find any documentation about this in the BBB manual
>and the processor manual is not much more forthcoming. The processor
>manual told me that the ADC can use either internal or external
>reference but I could find nothing further about it at all.
If you know the register name that is used to select between internal
and
external ref, then use ³git grep <reg-name>² to find where that register
gets used in the kernel source. If there is no reference to this
register,
then the default value will be used.

That's the problem, I can't find any documentation anywhere that tells
me about the internal/external switching. The whole of the ADC system
is shrouded in mystery! :slight_smile:

drivers/mfd/ti_am335x_tscadc.c

>> [-- text/plain, encoding quoted-printable, charset: ISO-8859-1, 43
>>lines --]
>>
>> External. Or internal. Or whichever one you want to use.
>>
>So it's selectable by software? What does it default to using at
>power on? I can't find any documentation about this in the BBB manual
>and the processor manual is not much more forthcoming. The processor
>manual told me that the ADC can use either internal or external
>reference but I could find nothing further about it at all.
If you know the register name that is used to select between internal
and
external ref, then use ³git grep <reg-name>² to find where that register
gets used in the kernel source. If there is no reference to this
register,
then the default value will be used.

That's the problem, I can't find any documentation anywhere that tells
me about the internal/external switching. The whole of the ADC system
is shrouded in mystery! :slight_smile:

drivers/iio/adc/ti_am335x_adc.c:#include
<linux/platform_data/ti_am335x_adc.h>
drivers/mfd/ti_am335x_tscadc.c:#include
<linux/platform_data/ti_am335x_adc.h>
drivers/misc/cape/beaglebone/bone-iio-helper.c:#include
<linux/platform_data/ti_am335x_adc.h>
drivers/misc/cape/beaglebone/cape-bone-geiger.c:#include
<linux/platform_data/ti_am335x_adc.h>

Regards,

John