Re: Accessing Raspberry Pi GPIO through EPICS

[Peter Milne <peter.milne@d-tacq.com>]

Hi Peter

If your use of gpio is the "switch a bit on, switch it off sometime 
later" type,
then the linux kernel gpio support will probably do it for you:

eg from the shell control would be:
echo 1 > /sys/class/gpio/gpio100/value

We use that interface extensively with an ioc; we wrote a very thin 
layer of device support that reads/writes single values from/to a 
virtual file and fits it into an appropriate record. A small set of 
abbreviations makes the db support palatable.

eg for BO record type, in the device support:

/** @file devBoAcqHost.cpp Device support entry for BO records
 *
 *  Created on: May 3, 2012
 *      Author: pgm
 *      BO:
 *      INP = path to knob, write 0 or 1.
 *      specials:
 *      %g KNOB : /sys/class/gpio/KNOB/value
 *      eg %g gpio100
 *      %l KNOB : /sys/class/leds/KNOB/brightness {1|0}
 *      eg %l cpsc:1:green:idle
 */

in the db file:

record(bo, "${UUT}:PSU:RESET:${cid}") {
        field(DTYP, "boAcqHost")
        field(OUT, "@%g gpio${gpio_reset}")
        field(DESC, "reset PSU ${cid}")
        field(ZNAM, "OK")
        field(ONAM, "ERR")
        field(PINI, "YES")
}

record(bi, "${UUT}:SYS:exttrg2") {
        field(DTYP, "biAcqHost")
        field(INP,  "@%g gpio22")
        field(DESC, "front panel input WAVTRIG")
        field(SCAN, "1 second")
}

I'd be very happy to send you a copy of the source if you're interested.

Cheers

Peter.




On 14/08/13 08:25, Florian Feldbauer wrote:
> Hey Peter,
>
> to access the GPIOs from EPICS you need to write a device support 
> module using the C-libraries.
> Unfortunately there is no good documentation on this topic for 
> beginners that I know of...
> I could provide you my device support for reading out DS18S20 
> Dallas-1-Wire Temperature sensors using the Pi as a starting point.
> Best regards,
> Florian
>
> On 08/14/2013 02:09 AM, Peter Linardakis wrote:
> > Hello all...
> >
> > We are exploring the idea of using Raspberry Pi for basic digital IO 
> > tasks. Theidea is that we could avoid deploying other IOCs and 
> > possibly wasting many other IOC ports. I have EPICS running on a 
> > Raspberry Pi with a test record DB (soft records only) and it is 
> > successfully communicating across the network.  I know how to 
> > directly access the GPIO pins while on the Pi (through C libraries 
> > etc.),but I do not know the first thing about how to get to those 
> > pins through EPICS.
> > Any advice or direction would be much appreciated.I am relatively new 
> > to EPICS development but am experienced with with maintenance of 
> > EPICS records and the like.
> > Regards
> > Peter
> >
> > Dr PeterLinardakis
> >
> > /Accelerator Research &Development Engineer/
> >
> > *Nuclear Physics | Research School of Physics and Engineering*
> >
> > *Australian National University*
> >
> > e: peter.linardakis@anu.edu.au
> >
> > p: (02) 6125 2862
>
> --
> ----------------------------------------
> | Dr. Florian Feldbauer                |
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> | Helmholtz-Institut Mainz /           |
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--
Peter Milne			Peter.Milne@d-tacq.com
D-TACQ Solutions Ltd		www.d-tacq.com