[Arm-netbook] Testing: GPIO

[Christopher Havel]

Posting from my phone while making dinner, so forgive that it's a top-post
plz.

Testing via the micro desktop works as long as you've got a known good
micro desktop and your ports haven't won through. I think the 4051 idea
might be a little better - I've worn out USB ports before, just from using
them - ask me sometime about my mother's old VAIO laptop and how it
ultimately died... the only thing in my test rig to wear out is the card
cage...

But, I'm not in charge, so I'll defer.

On Mar 1, 2018 7:04 PM, "Richard Wilbur" <richard.wilbur at gmail.com> wrote:

> 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
>
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