Re: [9fans] Pi updates

[erik quanstrom <quanstro@quanstro.net>]

On Fri Jan  1 21:15:03 PST 2016, blstuart@bellsouth.net wrote:
> On Fri, 1/1/16, erik quanstrom <quanstro@quanstro.net> wrote:
> > i'm looking @ the gpio interface, and i wonder what the recommended
> > technique for sampling a pin might be from a shell script?
> 
> I haven't really used it in shell scripts, but if I were going to do
> so, I'd probably write up a little utility to take a hex string and
> a bit number and do the 'and' on it.  Then feed that with the
> result of dd to get exactly one sample from devgpio.  On the
> other hand, if one of the usual suspects (e.g. hoc, bc, dc, awk)
> have some bit-wise operators I'm forgetting, use that.

the (atom) aux/number program does do that; none of the others do
for fairly fundamental reasons: as awk and hoc are really floating
point, and bc and dc are mp, and the mp library has no bit operations.
i believe acid can as well, but only with great pain.

perhaps just using base 2 for the encoding would make life a lot easer. so 

00000000000000000000000000010000000000000000000000000000000000000

for bit 27 active.  with this format there's no limit to the number of bits one
could represent.

also, mightn't there be some value in presenting the full state of the device
to allow it to be restored directly from the status file, so perhaps 3 lines
could be added, one each for up/down/float settings?

00000000000000000000000000010000000000000000000000000000000000000
00000000000000000000000000010000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000

might represent bit 27 set, with the pull up resistor active.  (perhaps
float ≡ (pullup | pulldown) == 0? and could be elimitated.

i'm sure a little tinkering with this idea can make it a lot more useful.

- erik