[Arm-netbook] Testing: GPIO

[Richard Wilbur]

On Thu, Mar 1, 2018 at 4:12 PM, Christopher Havel <laserhawk64 at gmail.com> wrote:
> I /designed/ that circuitry in the micro-desktop. I still have the paper
> copy somewhere...

Very nice!

> You can also do it with a dedicated DAC chip, which is the
> easy-but-expensive way I hinted at.
>
> But we aren't testing /that/ part -- the micro-desktop -- are we? If we're
> testing the /card/, the card does not output anything remotely like VGA,
> and, therefore, some kind of conversion is necessary in order to attach it
> to a VGA cable as was being proposed in the email I replied to about that.

We aren't planning to test the micro-desktop.  The planning is for
tests of the card mounted in a micro-desktop case to use as a test
fixture.  We are planning to use your good work on the micro-desktop
case to our advantage and connect the VGA cable to the micro-desktop
VGA connector in order to see that the EOMA68 RGBTTL (with EDID) works
as advertised!

> All you really need for this is a laptop PCMCIA or CardBus card cage, an
> IDE cable or two, a couple 4051s and toggle switches on a slice of
> perfboard, a 9v battery with connector and switch, and a cheap USB logic
> analyzer attached to a laptop. You use the 4051s, switched manually, and
> powered by the 9v battery, to act as input expanders for the logic
> analyzer. Each 4015 turns one channel into eight and requires three "on-on"
> switches -- with one "on" wired to +9v, one to ground, and the common to
> the chip. You use the IDE cable for the wires ;) If you hook it up so that
> you have one 4051 mux per logic analyzer channel, that'll give you 128 (!)
> channels to switch with -- most USB logic analyzers, even the super cheap
> ones, are 16-channel...
>
> Heck, if you wanted to make the circuit "complicated" -- I could draw up
> something that automatically iterated through the channels for you at the
> press of a single button, switching at variable speed with a pot, a 555, a
> resistor and cap, and a couple 4017s and 4051s. You'd only need /one/
> channel for that -- so you could even use an o-scope there. Heck, I could
> do it with that circuit and my old, old Tektronix 422...
>
> I'm honestly surprised that this sort of idea hasn't been mentioned yet.

That is a cool way to set up a very wide logic analyzer.  We were
planning to use a little specialized hardware and less elbow grease to
make our test fixture:
*  USB devices connected to the micro-desktop case USB ports,
*  SD peripheral connected to the micro SD slot,
*  VGA monitor connected to the VGA connector,
*  serial terminal connected to the UART pins in expansion header