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

[marcello c. <ca...@fi...>]

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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-- 
Marcello Carla'
(ca...@fi...)