[linux-dvb] Re: V4 API STC compare

[Johannes Stezenbach <js@convergence.de>]

Rob.McConnell@Zarlink.Com wrote:
> 
> I am planning on adding a "DVB_DMX_SET_STC_COMPARE" ioctl to my driver to
> allow a compare event to be setup in hardware.  When (and if) the STC event
> triggers (i.e. the value passed in by the syscall equals the actual STC
> value), the user process can determine this occurrence through using the
> standard "DVB_DMX_GET_EVENT" ioctl.  Also a "DVB_DMX_CLR_STC_COMPARE" ioctl
> would be used to clear/cancel this event if need be (e.g. channel change).

Fine by me. The advantage of using that instead a userspace timer is
that it would work with trick modes (e.g. if someone wants subtitles
in slow motion).

> I plan on adding:
> 
> #define DVB_DMX_NULL_EVENT
> #define DVB_DMX_STC_COMPARE_EVENT
> 
> to the current list.  If a process is waiting on this event and the
> "DVB_DMX_CLR_STC_COMPARE" ioctl is issued on the logical demux device, then
> the process would wake up and the event returned would be
> "DVB_DMX_NULL_EVENT".

What would DVB_DMX_NULL_EVENT be good for? Why not just return from the
blocking syscall with an appropriate errno?

Anyway, I would:

enum dvb_dmx_event_type {
	DVB_DMX_RECORDING_EVENT,
	DVB_DMX_STC_COMPARE_EVENT
};
struct dvb_dmx_stc_trigger {
	int enable;		// enable STC compare event
	uint64_t stc;		// 33-bit / 90kHz
};
struct dvb_dmx_event {
        enum dvb_dmx_event_type type;
        union {
                struct {
                        enum dvb_dmx_recording_event_type event;
                        uint64_t bytes; /* still not clearly defined */
                } recording;
		uint64_t stc;	// when DVB_DMX_STC_COMPARE_EVENT was queued
        };
};
#define DMX_SET_STC_TRIGGER _IOW(DVB_IOCTL_BASE, 0x4d, struct dvb_dmx_stc_trigger)
#define DMX_GET_EVENT _IOR(DVB_IOCTL_BASE, 0x4e, struct dmx_event)


The DVB_DMX_CLR_STC_COMPARE operation would be done by DMX_SET_STC_TRIGGER
with "enable" == 0.


OK?

Johannes


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