[Arm-netbook] Crowsupply update

[Luke Kenneth Casson Leighton]

---
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Fri, Jan 12, 2018 at 11:37 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:
> Last time I asked these questions I succeeded in hiding them in the middle of a bunch of other text.
>
> On Jan 9, 2018, at 06:26, Richard Wilbur <richard.wilbur at gmail.com> wrote:
>> What kind of logic are these GPIO pins?  (CMOS, TTL, etc.)
>
> The type of logic determines the input and output voltage and current
> source and sink characteristics (both capabilities and expectations).
> Do you have the Allwinner documentation for the A20--specifically for
> the GPIO pins?

 ok google "allwinner a20 datasheet" or better "allwinner a20
reference manual" you'll find it.


>> So there are 4 pairs or 8 GPIO lines to test? (I thought we
>> had more lines dedicated to GPIO and two more that were
>>going to be used as I2C for VGA?  Are only 8 easy to test?)

 the choice - on the Microdesktop PCB - to arbitrarily utilise two of
the GPIO pins as bit-banged I2C - is entirely one that is legitimate
yet has absolutely nothing to do with the EOMA68 specification,
*other* than, "It Is Permitted" under the EOMA68 specification to make
such decisions.

 the choice - on the Microdesktop PCB - to arbitrarily utilise those
two GPIO pins as bit-banged I2C - is done because the termination
impedance for VGA EDID is, according to the specification, somewhere
around 10 kOhms, whereas the normal I2C termination resistance is
usually somewhere around 2.2kOhms.

 i felt therefore that it was important *not* to have the VGA I2C
lines connected to the EOMA68 I2C bus.

 these decisions have *nothing to do with the EOMA68 specification*,
they are simply "permitted under the EOMA68 specification" if that
makes sense.

l.