On 03/17/2017 08:18 PM, Trần Ngọc Quân wrote:
> Hi,
> I try to read from system fs, but it don't work?
> Please see the attachment and help me fix it.
> Thanks in advance!

Realtime comps can't read from sysfs (or any files), but userspace comps 
(aka non-realtime comps) can.

There are a couple of bugs in your comp, and one bug in halcompile that 
prevents your comp from working.


The bugs in your comp are:

* You need to #include unistd.h for read() and usleep()

* You need to rewind the file descriptor using lseek() before each read

* And you should check the open() and read() for errors.


The bug in halcompile affects singleton userspace components, add this 
line to the top of your user_mainloop() to work around it:

struct __comp_state *__comp_inst = __comp_first_inst; 



I opened issue #245 to track the halcompile bug: 
https://github.com/LinuxCNC/linuxcnc/issues/245


-- 
Sebastian Kuzminsky

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