olafL66 wrote:If you want to support character set changes in RAM and screen memory together, you would be better off with a Graphic/Memory changes queue (like using part of the joint memory to queue up memory changes), so that you don't need to copy 4Kb repeatedly to keep the screen uptodate.
Also, you may want I/O to the SuperCPU, unless you only use it for calculations, still having the brunt of the program running under the internal 6502.
[Update] okay, now I went through ALL the thread entries, I see it's progressed quite a bit
And the VGA output from the Cartridge increases at least Graphics usability quite a lot !
Sorry, I'm not so often here.
The VGA is generated on the fly from the internal memory changes. If you poke a byte in the internal Vic-20 memory area (including color RAM), it gets mirrored into a buffer. Thus, there is no need to repeatedly copy any 4KiB area. This buffer is the source for the VGA signal generation (including graphics). The only part that I "cheat" at is the Character ROM that is pre-stored inside the SuperVixen.
The reason for the VGA was simply to make it easier to find a monitor for the Vic-20. The number of CRT's out there is starting to dwindle, and many composite to VGA converters doesn't cope with the Vic-20 video signals. If you have a working LCD with composite signal that is fine for you, but I currently only have a large TV that has such input (and I never get to use it for my Vic-20
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At the end of it, the VGA output will never be 100% compatible, but maybe 99%. As of now, 80-90% of the games seems to work. Some games get the graphics in the wrong places (a bug), and raster effects are not implemented yet (but I plan to do that eventually). The nice thing with this unit is that there is no modification or extra power supplies. You plug it in and it works.
As for the SuperCPU (65C02 at 25MHz), you don't need to use it, but it would speed up things considerably. The 65C02 can access the 32KiB "expansion memory area" that the Vic-20 sees (as a dual port memory), and it can access the 1MiB external SRAM on the card. All-in-all, the 65C02 will eventually be able to do most of what the 6502 of the Vic-20 can. Still, one wants to keep the 6502 running since that is the only way to have 100% compatibility with old software. I think its important with backward compatibility.
The best feature is currently the SDCard. The reason is that its fast. You can get all the Vic-20 software ever made onto one, and it takes milliseconds to load your favorite game/tool/utility. Currently SDCard SAVE does not work, but I hope to have it working by the end of this year.
At some point I need to stop the HW development and get things to production. I hoped to add a RTC, but that will probably only be as a space for the chip (nothing mounted). The first cards will be assembled manually, so my target (as of now) is to get that going in August. Final beta will therefor have to be finished by end of this month.