Well, if I undertood correctly, the problem would be the PPI, VDP and PSG that wouldn't be able to work with higher speeds, but you could change the ram and the z80 and using another crystal run your msx at 20 mhz or more. Of course that would require a lot of changes, but I wonder why we can't use it. I know that for graphics/sound/slots we would be stuck with 3.5 mhz, but I believe having the cpu doing its math, sending/receiving bytes from RAM and processing with 20 mhz would allow us to do softwares that now aren't possible in MSX. Is there a reason people never did this? For instance, I believe the z80 in my CIEL2+ has 10 mhz, but it is working with just 7 mhz. Couldn't be machines like mine running faster?

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but I wonder why we can't use it. I know that for graphics/sound/slots we would be stuck with 3.5 mhz, but I believe having the cpu doing its math, sending/receiving bytes from RAM and processing with 20 mhz would allow us to do softwares that now aren't possible in MSX. Is there a reason people never did this?

On the ZX81, there are two modes: the fast mode and the slow mode. In fast mode, there's no video output, so e. g. doing math is quite fast. In slow mode, the Z80's speed is lowered by doing video output. But actually, ZX81 isn't MSX!

The problem, is that it makes no sense upgrading speed, if the other IC could not be made faster. Look at R800: It is very fast compared to the z80, but for doing graphics (so for example fill vram or change a pixel color with another), that speed it is useless: performances are roungly the same as in z80 mode.

Another question would be if, for example we can made Gfx command and vram access more fast, roungly at the same degree of the cpu. So:

R800 = 8*z80 speed, NEWVDP=8*OLD_VDP_SPEED

Speeding up the only cpu would not be so a good idea if other components cannot be at the same level.

Remember AMIGA with the blitter? Originally on a 7mhz 68000 it was able to do twice the work of the cpu in graphics operations. But when amiga users started to upgrade the clock at 14-21 Mhz the BLITTER was the slow part of the system and commodore replaced it with a faster IC to compensate the difference.

I understand your point, but remember I didn't say it wasn't important to speed up the other IC's on MSX. I think it's not useless either to have a 20 mhz z80 in your MSX even if the rest (except the ram) is running at 3.5 mhz. There are many apps that can't be done in MSX due to lack of processor power. With a fast z80, you could use compressed data and do heavy calculations more often than it's done now. Wouldn't that be important as well?

A Z80H can't handle more than about 10MHz.

Indeed, I have a z80H on my CIEL, and it is exactly 10 mhz. But I was thinking about some other processor compatible with z80 code. But I think we are missing the point. I believe there are advantages of a fast z80 even when you are stuck with 3.5 mhz when you are 'talking' with PSG/VDP/PPI/Cartridges/ETC. Or there aren't any?

Certainly there is something to be gained with extra CPU cycles, even with the limitations of other parts of the machine like the VDP. Have you ever waited for a JPG to display? Zzzz...

As for the Amiga, the blitter never really did get upgraded. The latest AGA chipset had a wider bus and new graphics modes but it ran at the same clock speed as the original chipset. Users of upgraded Amigas often patch the OS so that the CPU is used for GUI routines instead of the blitter, or they install an SVGA card like on a PC and bypass the chipset altoghether.

After further testing, I have found that disabling the waitstate in my machine caused a lot of glitches with the VDP (particularly screen 0), so I guess it isn't much of an upgrade

Why speed up an MSX 1/2/2+?
Accept the limits of the system.

If you want to view jpg, play mp3, movies etc... use a modern pc/mac.
If you really want to do that on an MSX, we need a new hardware standard (MSX 3?) based on a Z380 or faster or the OCM.

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Certainly there is something to be gained with extra CPU cycles, even with the limitations of other parts of the machine like the VDP. Have you ever waited for a JPG to display? Zzzz... As for the Amiga, the blitter never really did get upgraded. The latest AGA chipset had a wider bus and new graphics modes but it ran at the same clock speed as the original chipset. Users of upgraded Amigas often patch the OS so that the CPU is used for GUI routines instead of the blitter, or they install an SVGA card like on a PC and bypass the chipset altoghether. After further testing, I have found that disabling the waitstate in my machine caused a lot of glitches with the VDP (particularly screen 0), so I guess it isn't much of an upgrade

Screen 0? Very strange! this mode has the lowest bandwidth requirements, so VDP should be more ready when comunicating with CPU. Are you sure that the problems are not greater in gfx modes? (pay particular attentions in sc4 and greater modes)

It's the same with my TurboR with 40MHz, but it's a bigger problem when I put it in z80 mode. Timing issue. I guess the screen driver just assumes the time it takes to put the characters or something. Seems to be mostly when scrolling the screen in text mode on my msx.

I did another experiment, added some logic so that waits are ignored for memory access but honored for I/O port access. Still there are glitches (although much less) when scrolling the text in screen 0. With games I don't see any problem except in Aleste 2 there is an incorrect tile in the background every once and a while.