Re: [Linux-gpib-general] Patch for linux-gpib GPIO bitbanging driver

[Thomas K. <ele...@gm...>]

Dear Marcello,

you are probably right setting the sn7516x_used flags to on by default.
I wanted to avoid hogging unused GPIO pins, but it is probably better
to have a safe default rather than having to tell every user to use
this obscure module parameter ... I'll document the whole thing
properly on my homepage in the next days.
The led was also a good find, i toggled it as an activity led in my old
code but this makes much more sense!

Thanks!
Thomas

On Sat, 24 Apr 2021 11:52:49 +0200
"marcello carla'" <ca...@fi...> wrote:

> hello,
> 
> Many thanks to Thomas Klima for the latest version of
> the gpib_bitbang driver with the upgrades.
> 
> I suggest two further little adjustments:
> 
> -------------------------------------------------
> diff  gpib_bitbang.c-thomas-latest gpib_bitbang.c
> 73c73
> < static int sn7516x_used=0;
> ---
>  > static int sn7516x_used=1;  
> 784c784
> <         gpiod_direction_output(ACT_LED, 0);
> ---
>  >         gpiod_direction_output(ACT_LED, 1);  
> 816a817
>  >         gpiod_direction_input(ACT_LED);  
> --------------------------------------------------
> 
> The first one sets the use of the SN75160/161 bus drivers
> by default. Everything will work fine in any case, either
> the chips are actually used or the gpib bus is directly
> connected to the Raspberry gpios.
> sn7516x_used=0, instead, leaves the four gpio lines that
> control the bus drivers uncommitted (available for another
> use) and only the direct gpib-gpios connection will work.
> 
> The second one makes the green led on thomas' board light
> when the module is loaded and switch off when unloaded.
> 
> =====================================================
> 
> I have made a test with the gpib lines connected to the
> gpios pins through resistors of 10 (ten) ohm value, with
> four instruments on the bus. Here are the results:
> 
> Line DIO4 (representative of all data lines):
> 
> Low: -9 mA  (the gpio line is sinking current) @ 270 mV
> High: 2 mA
> 
> Line NRFD (representative of all control lines):
> 
> Low: -10 mA @ 280 mV
> High: 1 mA
> 
> According to the numbers, operation of the Raspberry in
> this condition is safe and there is room also for some more
> instrument. I will test and report about this as soon as I
> can.
> 
> Operation with the SN7516x bus drivers though is safer and by
> far more advisable if one is not 100% certain of what can be
> going on his gpib bus.
> 
> Good bye
> 
> Marcello Carla'
> 
> 
> 
> 
> On 4/22/21 3:21 PM, dave penkler wrote:
> > Hi Thomas,
> > Excellent, thank you. Will apply your patch and test builds on the
> > weekend. cheers,
> > -Dave
> > 
> > On Thu, 22 Apr 2021, 13:16 Thomas Klima, <ele...@gm... 
> > <mailto:ele...@gm...>> wrote:
> > 
> >     Hi,
> > 
> >     congratulations on the newest release of linux-gpib - I love
> > that the bitbanging driver is now included in linux-gpib!
> > 
> >     Since 2016 i developed a GPIB-shield for the raspberry pi and a
> >     patch to linux-gpib as driver on my project page
> > (elektronomikon.org <http://elektronomikon.org>).
> > 
> >     Marcello helped me with an interrupt-driven design, and his
> > current version is much more elegant than mine but is missing two
> > features which imho would warrant looking after:
> > 
> >     1, The driver in linux-gpib V4.3.4 is uses the legacy gpio
> > kernel interface which is marked deprecated for some time now. The
> >         raspi_gpib driver uses the GPIO descriptor based interface.
> >     2, My project includes SN75160/161 driver IC's which need three
> >         extra pins and are unused in the upstream driver.
> > 
> >     So i added both changes to the upstream version, which yields
> > the following file:
> >     https://github.com/elektronomikon/raspi_gpib_driver/blob/master/for_linux-gpib-4.3.4/gpib_bitbang.c
> > 
> >     Marcello tested this on his hardware which ran fine.
> > 
> >     The use of SN75160/161 is currently en/disabled via a module
> > parameter, which i think is an acceptable solution. Aa config file
> > switch would be another possibility, but i dont know how to
> > implement this... Any hints are appreciated :-)
> > 
> >     Patch is attached, please apply.
> > 
> >     Greetings,
> >     Thomas Klima
> >     _______________________________________________
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> > 
> > 
> > 
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