Additionally, I'm not really sure if the above description I gave will be fast enough, If you're very careful in how you structure your code, and making sure not to use function calls that switch back and forth between userspace / kernel space. I think it could be. However, if it is not fast enough still, you can use one of the PRU's to trap interrupts on a pin. But here the only missing piece I am not sure how you could generate a time stamp in a timely fashion. No pun intended.
Something to be aware of. If you're going to use something like printf(). That would definitely slow down such an application. *UNLESS* you were to pipe the output of that application to a file. LIke: ./foo > somefile.txt On Wed, Oct 19, 2016 at 8:31 PM, William Hermans <yyrk...@gmail.com> wrote: > > > On Wed, Oct 19, 2016 at 4:50 PM, Arthur Caio <arth...@gmail.com> wrote: > >> Hello you all! >> >> I need to calculate hot much time it takes for an input to go from LOW to >> HIGH and then to LOW again. Basically, I want to know the period of a >> square wave generated by the LM555 timer. >> >> I am using Qt Creator and programming in C++. >> >> I am having trouble at programming this code in C++ for the beaglebone. >> >> Do you guys have any piece of code in C++ that may help me? >> > I do not personally know of any code for this specific case. However, and > with that said. Your best bet aside from writing a Linux module > specifically for this is to use and interrupt, and some form of Linux time > API call. > > As for userspace interrupts. This is not really possible. As this would > slow down the OS too much because of application context switching. > However, there is something very close to just as good. For this from a > userspace application. You can setup a blocking read form the sysfs gpio > "value" file. Like so: > > $ ls /sys/class/gpio/gpio2 > active_low device direction edge power subsystem uevent > > *value* > > This is actually more complicated than it may seem initially however. As I > believe poll(), and select() both will return immediately if you do not > configure the "edge" file correctly. Instead of repeating what's already > been described on the internet, I'll leave you with this link, which > describes it this very well I think: https://www.linux.com/learn/ > beaglebone-black-how-get-interrupts-through-linux-gpio > > Then once you have that figured out, all you really need is a before, and > after timestamp. Which is described very well in the multiple answers to > this stackoverflow question; http://stackoverflow.com/ > questions/11765301/how-do-i-get-the-unix-timestamp-in-c-as-an-int > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CALHSORpKm%3DatwpZyZ780rayeFb74sK7m6h7ZN%3DQQmb3yj9D6UA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
