Hello again, Arnoud. I have been trying to access the B+ GPIO with the code you suggest above, but without success. I can write to GPIO13 using c code found at http://guillermoamaral.com/read/rpi-gpio-c-sysfs/ and it works fine. I believe it is using the same OS calls as are being called from your code. With the c code, I can write to GPIO13 in a loop and see the waveform on a scope. With the Wofram code I get nothing.
I have tried the wolfram code both by typing it in, and by executing as a script using "sudo wolfram -script myscript.wl" -- nothing happens.
Any ideas?
Best, David