DH_RegisterPoint,
DH_RegisterExistingPoint
DH_RegisterPoint,
DH_RegisterExistingPoint — register with the Cascade DataHub
for a point.
Syntax
#include <cogent.h>
ST_STATUS DH_RegisterPoint( | IP_hTASK | myself, |
| | PT_pCPOINT | ppoint, |
| | IP_hMSG | hmsg, |
| | ER_hLIST | elist); |
ST_STATUS DH_RegisterExistingPoint( | IP_hTASK | myself, |
| | PT_pCPOINT | ppoint, |
| | IP_hMSG | hmsg, |
| | ER_hLIST | elist); |
Arguments
- myself
- The
task handle associated with this task. This should always be
the return value from IP_NserveInit.
- ppoint
- A
pointer to a Cascade DataHub point structure, which must contain at
least name. All other fields in the point
structure should be 0 if this is the first
call on this point, because they will be filled in by this
call. Subsequent calls on the same point do not require
zeroing any fields. If one point structure is used with
several point names, the address field must be zeroed each time
a different name is used in a call to this
function.
- hmsg
- A
handle to a previously allocated message structure (using IP_MsgCreate) providing enough
buffer space to handle the inter-process communication
associated with the DataHub transaction.
- elist
- A
return value containing error information. This is unimplemented in this
version, and should be NULL.
Returns
ST_OK on
success, ST_ERROR on failure, or some other
value of ST_STATUS.
Description
This function informs the DataHub that this task should receive
exceptions (value change notifications) for the named point. The
DataHub will not generate an initial exception on the point, but
instead returns the current value of the point in the
ppoint structure. Subsequent exceptions will
be transmitted to the task as type=IP_ASYNC
messages with command=ST_EXCEPTION or
command=ST_ECHO. DH_RegisterPoint
will create the point on the DataHub if it does not exist.
DH_RegisterExistingPoint will return an error
if the point does not exist.
