Jump to content

Defender on Intellivision is confusing me. Help!


Recommended Posts

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.



  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...