[beagleboard] Re: Make PRU-controlled pin change direction or go tri-state?

[Andrew P. Lentvorski]

On Thursday, January 16, 2020 at 8:39:20 AM UTC-8, TJF wrote:
>
>
> In order to change direction for a pin on a GPIO-SS, it needs a write 
> access to its OE register. The PRU can do that.
>

Let me see if I have this straight, I need access to an output enable from 
the PRU.  The only output enable I can see involves the Industrial Ethernet 
Peripheral.

So, by setting the PINMUX up front to the IEP, I can route my data through 
the IEP DIGIO in order to gain the tri-state capability I want?

That ... might actually be what I need.

Thanks.

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Re: [beagleboard] Re: Make PRU-controlled pin change direction or go tri-state?

[Jason Kridner]

On Thu, Jan 16, 2020 at 11:39 AM TJF  wrote:

> There's no supervisor mode for the PRU.
>
> There's no tri-state-mode for AM335x GPIO.
>
> In order to change direction for a pin on a GPIO-SS, it needs a write
> access to its OE register. The PRU can do that.
>
> Find an example at
> https://github.com/DTJF/libpruw1/blob/master/src/bas/w1_prucode.p, which
> is a driver for a one-wire (w1) bus, reading and sending data on a single
> GPIO line for multiple divices. The library documentation is at
> http://users.freebasic-portal.de/tjf/Projekte/libpruw1/doc/html/
>

Thanks for the great example!

For those that don't quite follow, you are using the chip-level or
SoC-level GPIO subsystem for this example and not the PRU subsystem GPIOs
that can be accessed directly from R30/R31 on the PRU CPU itself. For those
pins, the PADCONF or pinmux settings must be adjusted at the chip/SoC-level
to disable the PRU GPIO output.


>
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> .
>

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[beagleboard] Re: Make PRU-controlled pin change direction or go tri-state?

[Dimitar Dimitrov]

I don't think you can tri-state PRU output GPO. But you can hook external 
buffer (e.g. 74HC245) and dedicate one PRU GPO for output enable.

Regards,
Dimitar

On Thursday, January 16, 2020 at 6:39:20 PM UTC+2, TJF wrote:
>
> There's no supervisor mode for the PRU.
>
> There's no tri-state-mode for AM335x GPIO.
>
> In order to change direction for a pin on a GPIO-SS, it needs a write 
> access to its OE register. The PRU can do that.
>
> Find an example at 
> https://github.com/DTJF/libpruw1/blob/master/src/bas/w1_prucode.p, which 
> is a driver for a one-wire (w1) bus, reading and sending data on a single 
> GPIO line for multiple divices. The library documentation is at 
> http://users.freebasic-portal.de/tjf/Projekte/libpruw1/doc/html/
>

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[beagleboard] Re: Make PRU-controlled pin change direction or go tri-state?

[TJF]

There's no supervisor mode for the PRU.

There's no tri-state-mode for AM335x GPIO.

In order to change direction for a pin on a GPIO-SS, it needs a write 
access to its OE register. The PRU can do that.

Find an example at 
https://github.com/DTJF/libpruw1/blob/master/src/bas/w1_prucode.p, which is 
a driver for a one-wire (w1) bus, reading and sending data on a single GPIO 
line for multiple divices. The library documentation is at 
http://users.freebasic-portal.de/tjf/Projekte/libpruw1/doc/html/

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