GDSX Manual

Design and Development
Extended General Device Support (GDSX) Manual–134303
2-13
Memory Management
plus the TSCODE-supported utility procedures ^CHECKPOINT, DO^CP, FAULT,
STOP^TASK, WAITED^IO[X], and WAIT^EVENT need to be considered when
determining when a task will be suspended.
USCODE must communicate with external requesters by calls to ^READUPDATE[X]
and REPLY[X] on pseudo-$RECEIVE files created and managed by TSCODE for the
DEVICE^HANDLER tasks. See the tutorial in Section 5 for details.
Memory Management
Because the working stack images of tasks are swapped to and from an extended data
segment, I/O operations must be performed by means of global buffers, and large
amounts of data local to tasks are best maintained somewhere other than the tasks’ stack
images. To facilitate the efficient use of memory by both TSCODE and USCODE,
TSCODE provides local memory pools and extended data segment memory pools, as
well as the following memory pool management procedures:
In order to be consistent with TSCODE, when managing the available global memory
pools, USCODE should use these procedures rather than another means. For further
information on these procedures see Section 8, “Service Routines.” For further
information on memory pools, see "Memory Pools" on page 2-23.
Although it is not generally advisable, USCODE can use its own extended segment
through calls to ALLOCATESEGMENT and USESEGMENT. The segment IDs
available to USCODE range from 0 through 1023. Such a segment cannot be
checkpointed with a call to ^CHECKPOINT(2), so this kind of space should be
considered temporary working storage.
Intertask Communication
TSCODE provides a set of procedures to support communication between TSCODE and
USCODE, and communication among user tasks. These procedures make it possible for
a DEVICE^HANDLER task to communicate with other DEVICE^HANDLER or
LINE^HANDLER tasks, and for a LINE^HANDLER task to communicate with other
LINE^HANDLER tasks.
The procedures also provide a mechanism for a LINE^HANDLER to efficiently handle
several different types of asynchronous events. The WRITE^ITC^MESSAGE[X]
GETEXTPOOL
GETEXTPOOLX
GETLOCALPOOL
PUTEXTPOOL
PUTLOCALPOOL
Caution. TSCODE expects that if USCODE changes the segment ID from m to n, immediately
after USCODE next relinquishes control, the segment ID has been restored to m. Therefore,
once a user task is using its own segment, it must not relinquish control until the previous
segment ID has been restored.