Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Examples
if ((sts = iofunc_devctl_default (ctp, msg, ocb)) !=
_RESMGR_DEFAULT)
{
return (sts);
}
// 2) see which command it was, and act on it
switch (msg -> i.dcmd) {
case DCMD_AUDIO_SET_CHANNEL_MONO:
audio_set_nchannels (1);
break;
case DCMD_AUDIO_SET_CHANNEL_STEREO:
audio_set_nchannels (2);
break;
case DCMD_AUDIO_SET_SAMPLE_RATE_CD:
audio_set_samplerate (44100);
break;
case DCMD_AUDIO_SET_SAMPLE_RATE_DAT:
audio_set_samplerate (48000);
break;
// 3) in case it’s a command that we don’t recognize, fail it
default:
return (ENOSYS);
}
}
// 4) tell the client it worked
memset (&msg -> o, 0, sizeof (msg -> o));
SETIOV (ctp -> iov, &msg -> o, sizeof (msg -> o));
return (_RESMGR_NPARTS (1));
Step 1
In the first step, we see again the use of a helper function, this time
iofunc_devctl_default(), which is used to perform all default processing for the
devctl() function. If you didn’t supply your own io_devctl(), and just let
iofunc_func_init() initialize the I/O and connect functions tables for you, the
iofunc_devctl_default() function is what would get called. We include it in our
io_devctl() function because we want it to handle all the regular POSIX devctl() cases
for us. We examine the return value; if it’s not _RESMGR_DEFAULT, then this means
that the iofunc_devctl_default() function “handled” the request, so we just pass along
its return value as our return value.
If the constant _RESMGR_DEFAULT is the return value, then we know that the helper
function didn’t handle the request and that we should check to see if it’s one of ours.
Step 2
This checking is done in step 2 via the switch/case statement. We simply compare
the dcmd values that the client code would have stuffed into the second argument to
devctl() to see if there’s a match. Note that we call the fictitious functions
audio_set_nchannels() and audio_set_samplerate() to accomplish the actual “work”
for the client. An important note that should be mentioned here is that we’ve
specifically avoided touching the data area aspects of devctl() — you may be thinking,
April 30, 2009 Chapter 5 • Resource Managers 265