software takes time to execute.
On 8/10/2020 7:09 AM, Mark A. Yoder wrote:
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
<jo...@allwinedesigns.com> 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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