5.3 ODEV Messages and Their Parameters

5.3.14 OPlay

#define OPlay				'Oply'
 

void playProc(OPlayParams *params, long ID);
 

typedef struct {
	long refNum;		
	long *onset;		
	long duration;		
	long *actual_duration;
} OPlayParams;
 

long refNum; In - The reference number of the stimulus to be displayed.

long *onset; Out - A pointer to a long variable to be filled in by the ODEV with the onset time of the stimulus.

long duration; In - The requested duration of the stimulus in milliseconds, for ODEVs that handle their own durations.

long *actual_duration; Out - A pointer to a long variable to be filled by the ODEV in with the actual duration of the stimulus, for ODEVs that handle their own durations.

Note: This message must be called through a message table.

This message tells the ODEV to display the stimulus referred to by refNum. The millisecond time at which the stimulus is actually displayed, as closely as can be determined by the ODEV, should be written to *onset.

The requested duration of the stimulus is passed in in via duration, for those ODEVs which handle their own durations. If the ODEV handles its own duration, it should display the stimulus this amount of time, as closely as can be determined by the ODEV. If the ODEV is handling its own durations it must clear the stimulus on its own and it will not receive an OClear message from the Trial Manager to clear it, but the Trial Manager still needs to know when the stimulus was cleared, so the ODEV must fill in *actual_duration with the actual time in milliseconds that the stimulus was displayed for. (See "11.5.1 Timing")

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