[atari7800] Re: DLIs?

Hello,
Firstly, take my advice with a grain of salt, as I've done very 
little actual programming for this wonderful beast.  I do, however, 
feel like I have a reasonably good grasp on how the graphics hardware 
should theoretically work.

> Now I have a question about the DLI. In the MARIA doc it states...
> "One of the bits of a DLL entry tells MARIA to generate a Display 
> List Interrupt (DLI) for that zone. The interrupt will actually 
> occur following DMA on the last line of the PREVIOUS zone."
> 
> Is it possible to have a DLI point to another DLL? From reading 
> this it says it's limited to a scan line unless I'm reading it 
> wrong. It would be nice to have a DLI spin off to another DLL so 
> the screen could be split vertically with two "kernels" running.

First, let me see if I follow you: You want to be interrupted in the 
middle and end of every scanline so you can swap between two 
different DLLs, correct?

I'm pretty sure this is basically not possible, as when MARIA is 
doing the DMA transfer of a scanline worth of graphic data, it halts 
the CPU so that this kind of tomfoolery doesn't occur.  When it wakes 
up, the scanline is already safely tucked away where your code can't 
touch it.  So put away those notions of cycle-counting to the middle 
of the scanline to do the switch, as well =]

Jeremy
----
Jeremy Penner - Coder, Artist, Jibba-Jabberin' Fool
jeremypenner@xxxxxxx       http://sporktania.ods.org/~jeremy/

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