Each stream handler may, or may not, be able to generate or receive sync pulses. This capability for each stream handler is defined in the SPCB for that stream handler. Synchronization pulses are passed as an event from the master stream handler.
Synchronization pulses are distributed by the Sync/Stream Manager based on the synchronization relationship of the programmed stream. This distribution is effective for both DLL and device driver stream handlers. Device driver stream handlers receive sync pulses through their sync pulse SYNC_EVCB. Each slave stream handler must regularly update the sync pulse SYNC_EVCB with its calculated stream time. The Sync/Stream Manager checks this slave-handler stream time against the master stream time and decides whether to send a sync pulse to this handler. The device driver stream handler checks for sync pulses from the Sync/Stream Manager by polling a flag in the sync pulse SYNC_EVCB. The Sync/Stream Manager sets the flag to indicate a sync pulse and updates the current master stream time. Typically, the PDD slave handler polls the flag once during interrupt processing and adjusts the stream usage accordingly. Refer to the following example for an example of how device driver stream handlers support synchronization.
/*****************************************************************/
/* If we are the master, then report the time so that the slaves */
/* can adjust their time and be in sync with the master. */
/*****************************************************************/
if ((pSTREAM)->ulStateFlg & STREAM_MASTER_SYNC) {
(pSTREAM)->SyncEvcb.mmtimeMaster = mmtimeCurrStreamTime;
RptEvent.ulFunction = SMH_REPORTEVENT;
RptEvent.hid = (pSTREAM)->hid;
RptEvent.hevent = 0; /* must be 0 for implicit events */
RptEvent.pevcbEvent = (PEVCB)&((pSTREAM)->SyncEvcb);
VideoSH.pSMHEntryPoint(&RptEvent); /* report master time */
}
/**************************************************************/
/* If we are the slave, then update slave time */
/* and determine if this slave stream is too slow or too fast */
/* with respect to the master. */
/**************************************************************/
if ((pSTREAM)->ulStateFlg & STREAM_SLAVE_SYNC) {
(pSTREAM)->SyncEvcb.mmtimeSlave = mmtimeCurrStreamTime;
if ((pSTREAM)->SyncEvcb.ulStatus & SYNCPOLLING) {
if (mmtimeCurrStreamTime > (pSTREAM)->SyncEvcb.mmtimeMaster)
/* I need to slow my stream */
;
if (mmtimeCurrStreamTime < (pSTREAM)->SyncEvcb.mmtimeMaster)
/* I need to speed up my stream */
;
}
Note: See Synchronization Features for more information on sync pulse generation and processing.