Beaglebone & C

Question

I've been playing with I/O ports in Javascript, that works fine, but basically I'm a C programmer. I want to do the same, read a sensor and turn things on & off with the beaglebone using C. The only information I've found so far is a wiki about embedded C that references a header file, iohw.h that makes it all possible, but which doesn't exist within the C compiler in the Angstrom or Debian distributions. Shall I assume that what I want to do cannot be done in C on the beaglebone? A standard ansi C manual has nothing on the topic for obvious reasons, and if there's any documentation for the beaglebone's C compiler it has escaped my searches so far. Can this be done, and if so, what is the function to write a bit to gpio44 or read a bit from gpio46?

mconners · Accepted Answer

BTW, though, the things you gain by using an OS are incredible as well, you don't have to include your disk IO routines in every program, you don't have to worry about user IO, networking etc. But there are tradeoffs. Mike

johnbeetem · Answer

I've accessed GPIOs on a Beagle Board using mmap(). Here's an old Google Groups thread on the topic: https://groups.google.com/forum/#!topic/beagleboard/_29qqEOv2VA I suspect the Bone is similar, with different addresses. You will probably have to "sudo" to be able to mmap() the GPIOs directly. The thread has some other methods that may be easier.

mconners · Answer

Realize that is one of the things you give up when going from bare metal to working with an operating system. The OS becomes the gatekeeper between you and the underlying hardware. This is by design. There are concepts that the beagle bone uses where they expose the pins via device drivers. This is how bonescript works underneath. It's been a while since I have looked at it, but I know it's there and with a little research you could probably find it. The next best thing would be to write your own device driver that behaves the way you want it to. There are free documents available on writing linux device drivers, so maybe that is a direction you could go. I'll try to take a look around this weekend and see if I can find the sources I used when I looked into this earlier. Good luck, learn and have fun, Mike

Beaglebone & C

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