Tuesday, February 19, 2013

Dexter update: Sony LDP-1000A probably won't make the cut

As you may have noticed, I have been exploring various video capturing technologies lately.  Part of the reason is to see if we can have more control over the video output signal than what the Raspberry Pi gives us.  Why?  Because of two reasons:
1) the Raspberry Pi does not let us control the VBI data that contains the frame numbers
2) the Raspberry Pi does not let us control when vsync occurs

Reason #1 is important because some players (PR-8210 and PR-8210A) are essentially output-only players and do not give the game any feedback as to whether they are functioning correctly.  In order to know whether the player is working, the game hardware needs to read the frame number from the VBI data.  So the fact that the Raspberry Pi does not let us control this VBI data was problematic.  However, I believe that we have discovered a way (and we will pursue it) to inject VBI data into the video signal in real-time (which is very cool).  So things are looking good for the PR-8210 games (Cliff Hanger, Goal to Go, MACH 3, and Us Vs Them off the top of my head).  Things are looking fairly good for Star Rider (PR-8210A) but it is still way too early to say with confidence that Dexter will definitely work with Star Rider.  But I am feeling good about the other four games at this point.

As for Reason #2, it turns out that the Data East games which use the Sony LDP-1000A (Bega's Battle, Cobra Command, Road Blaster) tell the laserdisc player when vertical sync occurs (unless I am very much mistaken) which is backward from how every other game works (the laserdisc player tells the game when vsync occurs).  I really am mystified how the laserdisc player can let an external source dictate when vsync occurs.  But regardless, this is something that I am quite sure the Raspberry Pi _cannot_ do (allow an external source to dictate vsync).  So the solution is for us to control the video signal more directly (ie through a DAC).  But at this point, I feel that going down this road would extend the release date of Dexter by a year at least, probably two to be realistic.  And I don't want to do that.  So I am hereby saying that as of now, Sony LDP-1000A support in Dexter v1.0 is out due to the constraints of the current design (ie using the Raspberry Pi).  I do eventually want to support this player, but I also want to ship a product!

That's the bad news.  The good news is that Sony LDP-1450 support is very much in and should be very good.  And the command protocol is almost the same between the 1450 and the 1000A.  So Dexter may still be able to be used with a Data East game but the game would require some hardware modifications (beyond my knowledge).

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