On Tue, 13 Apr 2021 11:25:06 -0700 (PDT), in
gmane.comp.hardware.beagleboard.user Walter Cromer
<walterc-2dFtBuzUeF/tpnmuczy8bueocmrvl...@public.gmane.org> wrote:
>We're designing it the way you suggested. The nice thing is that basically
>the control logic has already been written in C on the ARM side. Now, I
>just
>Here's one more thing I am struggling with though. It's a mental block I
>think. I'm used to controlling GPIOs on the ARM side using sysfs. It
>appears that on the PRU, we use __R30 instead but I don't understand how
>that works. I read through it this morning and it still isn't sinking in.
>If anyone can help make this clearer, I'd appreciate it.
>
More details of what is confusing you would help.
R30 (output)/R31 (input) registers are mapped as one GPIO per bit
https://elinux.org/Ti_AM33XX_PRUSSv2#Beaglebone_PRU_connections_and_modes
and those bits/GPIOs you are using will need to be properly pin-muxed in
u-Boot uEnv.txt.
As for using the registers... For input it should just be a case of
bitwise AND on the register content and test for result of 0/not 0
(assuming you are testing just one input at a time...). {Treat the
following as pseudo-code; I've not done any PRU programming, and am getting
stale with C]
inputX = 0 != (__R31 & (1 << desired_bit))
For output, you likely will need to maintain a copy (can the output
register be read by C code? -- if it can, forget the copy). You would AND
the inverse of the desired bit (to retain the other bits, but clear the
desired bit to 0) then OR the desired bit with the wanted value and write
the register with the combined result.
to set
__R30 = (__R30 & ^(1 << desired_bit)) | (1 << desired_bit)
to clear
__R30 = __R30 & ^(1 << desired_bit)
You'll likely want to prebuild the (1^^desired_bit) as constants for
each input/output of interest.
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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