I'm starting to play with gpiod on a Beaglebone Black. One of the
advantages of gpiod is you can toggle multiple pins on the same chip all at
once.
So I try:
while true; do
gpioset 1 18=0 19=0
gpioset 1 18=1 19=1
done
This is toggling pins P9_14 and P9_16. I expect to see the two pins toggle
on at the same time, but what I get is
a 4 microsecond delay from P9_14 switching and P9_16 switching.
*Should there be such a long delay? * I'd expect the two to switch at the
same time (which is what happens when toggle pins via the PRU).
I do the same experiment with python and I see a 70 us delay.
--Mark
On Friday, March 27, 2020 at 3:58:21 PM UTC-4 Drew Fustini wrote:
> On Fri, Mar 27, 2020 at 8:45 PM John Allwine <[email protected]>
> wrote:
> >
> > I don't intend to toggle a GPIO as fast as possible (except to test),
> but from a performance standpoint that demonstration seemed to indicate
> that there are issues with sysfs. Hopefully, libgpiod will prove to be
> better!
>
> Bartosz explains the differences and improvements that new gpiod
> interface provides in this talk:
> https://www.youtube.com/watch?v=cdTLewJCL1Y
>
> Essentially, if you need read or set multiple lines, it is faster.
> Also, it has an improved way to read events as well.
>
> Slides if you prefer over video:
>
> https://ostconf.com/system/attachments/files/000/001/532/original/Linux_Piter_2018_-_New_GPIO_interface_for_linux_userspace.pdf?1541021776
>
--
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