Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Porting philosophy
typedef struct
{
int data_rate;
int more_stuff;
} my_input_xyz_t;
typedef struct
{
int old_data_rate;
int new_data_rate;
int more_stuff;
} my_output_xyz_t;
typedef union
{
my_input_xyz_t i;
my_output_xyz_t o;
} my_message_xyz_t;
Here, we’ve defined a union of an input and output message, and called it
my_message_xyz_t. The naming convention is that this is the message that relates to
the “xyz” service, whatever that may be. The input message is of type
my_input_xyz_t, and the output message is of type my_output_xyz_t. Note that
“input” and “output” are from the point of view of the resource manager — “input” is
data going into the resource manager, and “output” is data coming from the resource
manager (back to the client).
We need to make some form of API call for the client to use — we could just force the
client to manually fill in the data structures my_input_xyz_t and
my_output_xyz_t, but I don’t recommend doing that. The reason is that the API is
supposed to “decouple” the implementation of the message being transferred from the
functionality. Let’s assume this is the API for the client:
int
adjust_xyz (int *data_rate,
int *odata_rate,
int *more_stuff );
Now we have a well-documented function, adjust_xyz(), that performs something
useful from the client’s point of view. Note that we’ve used pointers to integers for the
data transfer — this was simply an example of implementation. Here’s the source code
for the adjust_xyz() function:
int
adjust_xyz (int *dr, int *odr, int *ms)
{
my_message_xyz_t msg;
int
sts;
msg.i.data_rate = *dr;
msg.i.more_stuff = *ms;
sts = io_msg (global_fd, COMMAND_XYZ, &msg,
sizeof (msg.i),
sizeof (msg.o));
if (sts == EOK) {
*odr = msg.o.old_data_rate;
*ms = msg.o.more_stuff;
}
April 30, 2009 Appendix: A • QNX 4 to Neutrino 297