#37 GPIO on device mode support

[Jason Hwang]

Hi,
I'm trying to make this gpib_bitbang work on device mode, and trying to use a SN75162 instead of SN75161 so I think the hardware limitation of hardware support should be able to overcome. I would like to get some hint on what is needed to make that possible. And I saw on the changelog, there was a time and versions of gpib_bitbang.c supported device mode. Can you point me to that version and maybe some hint to what needed for device mode? I would like to try to make it work and happy to share and contribute on all efforts.

Thanks!

Best regards,
Jason

[DaveP]

Hi, 
We abandoned trying to implement device mode support since it was not possible to guarantee that the driver could respond within 200ns to ATN being asserted by the controller in charge. 
An additional hardware facility would be required that when DC is high on the SN75162 and ATN on the bus goes low then NDAC is asserted automatically on the bus by a hardware driver. 
Then, when eventually the gpio line for NDAC is asserted the hardware driver for NDAC is turned off.
A similar issue exists with the timing requirement for responses to parallel poll. Not having parallel poll support in device mode is however not a show stopper.
/d

[Jason Hwang]

Thanks Dave,

On the response to ATN, shouldn't it be able to be achieved if using
another interrupt handling for ATN?
And 2nd issue, can that be done by ATN interrupt to control SN75162's TE?
So when ATN is detected low, also assert TE so NDAC can be asserted. And
when data read completed, then also turn of TE to return NDAC.

I'm kind of in the studying phase but probably will continue to try it. I'm
actually using this on Beaglebone so also hoping Beaglebone performance
could be better than RPI. I'm actually trying to make it one to one between
controller & device, and only feature I needed to have for device mode is
STB and simple read/write.

On the other hand, can you help to point me where you setup initial
direction and values on the GPIB's management lines (ATN, IFC, SRQ, REN &
EOI)? I see settings on SN75161 but cannot find where it is initializing
gpio pins.

Thank you and appreciate your help.

Best regards,
Jason

On Fri, Oct 27, 2023 at 10:02 PM DaveP dpenkler@users.sourceforge.net
wrote:

Hi,
We abandoned trying to implement device mode support since it was not
possible to guarantee that the driver could respond within 200ns to ATN
being asserted by the controller in charge.
An additional hardware facility would be required that when DC is high on
the SN75162 and ATN on the bus goes low then NDAC is asserted automatically
on the bus by a hardware driver.
Then, when eventually the gpio line for NDAC is asserted the hardware
driver for NDAC is turned off.
A similar issue exists with the timing requirement for responses to
parallel poll. Not having parallel poll support in device mode is however
not a show stopper.
/d

---

[support-requests:#37]
https://sourceforge.net/p/linux-gpib/support-requests/37/ GPIO on device
mode support

Status: open
Group: v1.0 (example)
Created: Thu Oct 26, 2023 10:07 AM UTC by Jason Hwang
Last Updated: Thu Oct 26, 2023 10:07 AM UTC
Owner: nobody

Hi,
I'm trying to make this gpib_bitbang work on device mode, and trying to
use a SN75162 instead of SN75161 so I think the hardware limitation of
hardware support should be able to overcome. I would like to get some hint
on what is needed to make that possible. And I saw on the changelog, there
was a time and versions of gpib_bitbang.c supported device mode. Can you
point me to that version and maybe some hint to what needed for device
mode? I would like to try to make it work and happy to share and contribute
on all efforts.

Thanks!

Best regards,
Jason

---

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