Defender on Intellivision is confusing me. Help!

[+Lathe26]

How much of GRAM can be written to per frame (i.e. how many cards can be updated).  I don't think VBLANK is long enough to allow writing to all of the GRAM in one shot.

[carlsson]

It might depend on your programming environment, but e.g. the IntyBASIC manual says max 18 per frame, 16 if you're using the music player. That would be 1/4 of the total.

[+DZ-Jay]

3 hours ago, Lathe26 said:

How much of GRAM can be written to per frame (i.e. how many cards can be updated).  I don't think VBLANK is long enough to allow writing to all of the GRAM in one shot.

With a really optimized tight loop and ideal VBLANK conditions -- i.e., immediately upon request, and with no additional overhead -- I've managed to copy up to 24 or 26 contiguous cards.  Perhaps without posting the STIC shadow* it could do one or two more.

However, in a game, you hardly ever get ideal conditions, and IntyBASIC brings with it some overhead that is built into its ISR.

* (STIC register updates must be done before GRAM, since their period of accessibility is shorter than GRAM's.)

 

2 hours ago, carlsson said:

It might depend on your programming environment, but e.g. the IntyBASIC manual says max 18 per frame, 16 if you're using the music player. That would be 1/4 of the total.

I would take those numbers as a baseline, under ideal conditions.  Scrolling and switching screen modes, updating the Color Stack, and a fully-loaded music player can incur a bit of additional overhead.

 

In practice, with IntyBASIC, you should be able to count on about 16 contiguous cards copied with a single DEFINE.

 

Thats not bad.

 

   dZ.