There is pulse measurement hardware in the eCAP. Matt Porter submitted a kernel patch way back when: https://lkml.org/lkml/2014/1/29/413
On Mon, Oct 24, 2016 at 8:13 AM Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote: > On Sun, 23 Oct 2016 13:30:55 -0700 (PDT), Arthur Caio > <arth...@gmail.com> declaimed the following: > > >Hey everyone, > > > >I have a project with a LM555 timer and need to calculate how 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 did it with Arduino using the function Pulseln. But I need to do this > >using a Beaglebone and programming in C++ (Using QtCreator). > > > >Is there a way to "open" the function PulseIn so I know what it does? > > Sure... On my install it is found in: > > C:\Apps\Arduino169\hardware\arduino\avr\cores\arduino\wiring_pulse.c > > Though it invokes a hand-tweaked assembly routine for the main loop, in > wiring_pulse.S (for the AVR). > > Strange -- I have all the boards installed in the board manager, > but > can't find any files specific to the others. > > >Moreover, do you guys have any piece of code that might help me? > > > > You need to take into account that the Arduino is a microcontroller > (Atmel AVR for the most part -- the Due is an ARM M3, Zero is an ARM M0) -- > you have direct access to the hardware I/O pins. The Beaglebone is a level > higher, using an ARM A-series (application, not microcontroller) processor > under an operating system. > > The common pin access is via OS maintained "device files" (they > act as > files to the user, but aren't real files on storage), and one uses plain > POSIX/C I/O calls to open/read/close those files. That throws in a lot of > overhead and latency. Enough overhead that common DHT11/DHT21 humidity and > temperature sensors can not be read (they use a weird protocol where 1 and > 0 are determined by the length of HIGH following a start-of-bit LOW [1 is > ~80uSec, 0 is ~24uSec]). > > The next step up is the MMAP process -- where you directly map the > device registers into your program's address space, bypassing the OS file > system. You'll need to study the register layout to find which registers > control the pin you intend to read. You'll still be subject to OS > interference (it could swap your process out to run some other background > operation). > > The third step is to write the pulse sampling code using the PRU > (which > is a sort of microcontroller hiding in the same processor chip), and use > some form of IPC to have the main code tell the PRU to sample a pulse, then > send the result back to you. > -- > Wulfraed Dennis Lee Bieber AF6VN > wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/ > > -- > 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/gcsr0cdv9au5ofbkulsddptjjfvcjohehd%404ax.com > . > For more options, visit https://groups.google.com/d/optout. > -- 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/CA%2BT6QPkHC6Y4tpCnM9MN8a6iEjfmAKY40mdnM7YzcN3CTeFcEg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
