Posted By
MMS
on 2020-04-07
18:32:24
 |  Re: C64portal.pl has started - and it's not only c64 :)
@carrion, go on, i will definitely watch it  Thank you in advance.
New games are interesting
To see how you create graphics, would be VERY interesting.
@gerliczer:
I see your point, but I do not really see, why the double speed CPU would require completely new memory subsystem.
I would not change the TED clock frequency, just doubling the frq given to the CPU.
"TED has a higher priority on DRAM access then the CPU. Thus in the borders the CPU must be able to run at full system clock, but in the pixel area it is throttled down to half the clock rate."
If the half clock rate it is 1.76MHz (as on the border previously) it is exacly the speed how the CPU managed in the original configuration the memory at the borders.
Then the border time coming with 3,5 MHz. 6502's official highest clock rate was 3MHz. BBC Micro utilized 4MHz 65C02 cooprocessor, but had faster RAM chips with no shared memory (it was pretty fast).
But MCeS already has the solution, and I already use it as my 64K in C16: SRAM for the TED, that is definitely much faster, than the DRAMs, and it is just next to TED (no memory subsystem need to be rerouted):
Also worth to mention, that the 65C02 card could be more compatible than supposed (I do not own one), during tests behaved the same as 8501 even with fastloaders:
https://www.lemon64.com/forum/viewtopic.php?t=71571&sid=15ba4db8ef33c165c9f66396b141a96c
I think using a faster compatible processor should not be a "blasphemy" on +4, it was widely used in BBC Micros, AppleII, and even C64 had turbo card and had a Z80 card to run CP/M.
(sorry for the OFF)
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