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Fungus
Registered: Sep 2002
Posts: 629 |
REU and Color Memory
Can the REU access color memory or is it a quirk that it cannot?
I've not been able to get color memory scrolling to work with an REU and don't know if it's just a VICE bug or if this is intended. |
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tlr
Registered: Sep 2003
Posts: 1726 |
Quote: Can the REU access color memory or is it a quirk that it cannot?
I've not been able to get color memory scrolling to work with an REU and don't know if it's just a VICE bug or if this is intended.
Interesting question. The color memory is connected in a special fashion due to it being a separate bus on the VIC-II. The data bus to it depends on AEC for instance. I think it looks in the schematic like it should be accessable, but this should be tested on HW of course.
Do you have a small test program that someone with a REU could run?
Preferably a read/write color ram test with go/no-go if possible. |
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6R6
Registered: Feb 2002
Posts: 244 |
Correct zp 01 value when transfer? |
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Fungus
Registered: Sep 2002
Posts: 629 |
I don't have a test program atm, I was trying to fix a game with it but it didn't work so reverted the code in frustration. I just figured the REU can't access the color memory, but then I am using an older vice so thought it might be a bug in it (3.2).
I thought Sonic used it, so it was possible, but I can't get it work. I'll try again, maybe I just didn't code it correctly. Although I have been using the same code in my tape transfers without issue. |
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Mr. SID
Registered: Jan 2003
Posts: 423 |
Sonic only writes to Screen and Color RAM, it never reads. Maybe reading doesn't work, I've never tried that... |
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tlr
Registered: Sep 2003
Posts: 1726 |
No point in speculating here. I'll ask on #vice-dev if someone knows if this is tested, otherwise we need to see what it does on a real machine. |
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chatGPZ
Registered: Dec 2001
Posts: 11147 |
it should work (ignoring that transfers from/to I/O are glitchy on some setups)
https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/REU..
And yes, for REU things use recent VICE :)
PS: make sure REU transfers do not start or end at the same cycle as VICII DMA, that causes weird behaviour/glitches. VICE does NOT emulate this correctly atm.
https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/REU..
https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/REU.. |
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Fungus
Registered: Sep 2002
Posts: 629 |
What do you mean by "some setups" ? |
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chatGPZ
Registered: Dec 2001
Posts: 11147 |
Random C64s, reason unknown. It may or may not be related to the (known) glitches that happen when REU DMA starts (or stops) at the same time as a VICII DMA. In some of those demos that show 1 pixel wide color splits using REU, you can see glitches - on some C64s. |
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Fungus
Registered: Sep 2002
Posts: 629 |
Okidoki, I'll check that REU is not dmaing at the same time then. |
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Martin Piper
Registered: Nov 2007
Posts: 645 |
Do you need to avoid bad lines? |
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