Posted By
MMS
on 2023-11-02
16:35:16
 |  Re: Whirlybirds Sources (by Puls4r)
OFF
Citadel is more a Wolfstein 3D clone, not a Doom clone. still I feel it is a little slow.
Too bad, the Amiga did not have the fast 320x200 1 byte deep chunky video mode, just the much slower planar graphics.
QUOTE
"A chunky mode was a necessity in 1994 or even 1993, because the Amiga's bitplane system would require as many as eight separate operations in screen memory to write to eight bitplanes, to change ONE pixel, which would (and did) slow down Amiga graphics to one-eighth of the speed of a 1-bitplane mode. Faster processors and direct writing (bypassing the Blitter) can yield some good results, but the fast speed was needed on the standard "stock" Amiga A1200, and it was already underpowered compared to 386 and 486 PCs as it was, and that's even before the separate bitplane writes I mentioned before.
I've programmed on PC in chunky modes, and it really is very neat and easy and simple how each pixel can be plotted with 1 out of 256 colours with just one byte written to memory - no wonder programmers switched to PC as soon as they could."
UNQUOTE
This is the processing power an A600 require to able to run the Doom at proper speed. Vampire2 board with direct RAM access runs 9x (!) faster than an 50MHz 68030 CPU, do not to mention the original 68000.
https://www.youtube.com/watch?v=eM-bwuBJ644
Attribute gfx makes it even harder... So you need much more CPU processing power, but we do not have.
OFF OFF:
You know I mentioned several times the CPU upgrade, but seems it is not possible, or not a preferred idea by the scene.
When CPU gets the full clock from TED, it does not reach the screen, like on border. It could be any clock speed, like a much higher clock speed for WDC 65C02 CPU, even 14MHz. Switching the CPU to 1.76MHz from the TED frequency and back does not make any harm to the screen, why a 4MHz would do?
The main issue is the RAM/ROM access by the CPU. It simply cannot be faster in this way, the fast CPU would have been just waiting for the proper time to write and read.
The SAM Coupe had a 6MHz Z80 CPU, but due to the shared and slow memory access, it was just slightly faster than a 3.5MHz ZX Spectrum.
The 512k SRAM used in Lotherek 6502P4 could be great as it has no wait stages or speed constraints when CPU manipulates it, unfortunately all the ROM access has the same problem, not to mention the external IC's answering time.
The ROM problem could be easily solved, the solution is there in every PC we use. The Shadow BIOS ROM is a BIOS copied from the ROM into the much faster RAM, and the PC uses it instead of the slow (EP)ROM, makes the PC significantly faster. So the 512KB SRAM in Lotharek extension could me modified to use the lower half 256KB as a Hannes compatible RAM, the upper 256KB (or just the 64KB from it) can be used for ROM content fast access (Kernal, BASIC, 3+1) etc copied at startup from ROM to SRAM, and when bank switching happens, just add to the calls the +256KB address and you get the ROM.
I suppose even the BASIC would run significantly faster from SRAM, but maybe just had some crazy ideas :-)
The ICs (6551 and such) cannot be speeded up, I suppose, but the main issue is the +4 ROM and RAM access speed are not up to the higher CPU requirements.
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