Enabling / using expanded VDP addressing

[Willie1914]

Hi everyone,

 

I'm interesting in using the expanded VDP addressing feature in Classic99 -- I've read the documentation, but am not clear on exactly how to access the VDP Ram using this feature (i.e., register usage, register setup, etc.)

 

Can anyone direct me to further documentation or offer information?

 

Thanks in advance,

Bill

[Tursi]

Are you talking about the 2k of GPU memory on the F18A? Classic99 doesn't have any other expanded VDP memory I can think of.

 

If it's that memory, it's only accessible from the F18A's GPU. The F18A GPU is a 9900-compatible processor in the F18A that runs code from video memory, so you can just load code from the 9900 to VRAM, and then trigger the F18A to execute it. In that case, the GPU has RAM located from >0000 to >47FF.

[+Lee Stewart]

I think he is talking about the additional VRAM the TMS9938 is capable of supporting. If that is the case, your (Classic99’s) manual (page 20) is clear that VDP RAM of 128 KiB is supported as per the TMS9938. I did not get around to checking whether VDP registers beyond VR07 can be set in graphics modes (non-80-column text mode).

 

...lee

[Willie1914]

Thanks for the replies -- yes, I was referring to the "Enable 128k Hack" (page 20) feature of the TMS9938... any advice on where I may find more information?

 

Bill

[+mizapf]

You are talking about the v9938?

[Tursi]

Oh, right. That's not officially supported, but it's accessed in the 9938 manner. I can't help you much there.