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Enabling / using expanded VDP addressing


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#1 Willie1914 OFFLINE  

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Posted Wed May 15, 2019 7:45 AM

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


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#2 Tursi OFFLINE  

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Posted Wed May 15, 2019 3:00 PM

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.

#3 Lee Stewart ONLINE  

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Posted Wed May 15, 2019 4:24 PM

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



#4 Willie1914 OFFLINE  

Willie1914

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Posted Wed May 15, 2019 4:56 PM

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



#5 mizapf OFFLINE  

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Posted Wed May 15, 2019 5:44 PM

You are talking about the v9938?



#6 Tursi OFFLINE  

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Posted Thu May 16, 2019 11:12 AM

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




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