questions concerning 7Mhz upgrade

Prophet (2166)

02-02-2014, 22:03

I am allready planning to do this upgrade for almost as long as I got back into MSX but I just wonder about its pro's and cons. i read a lot of bad horror stories on the forums about pitched audio. Hanging on disk io etc etc. and also stories about the eventual frying of the DRAM and other components.

What problems will I run into anyway? how much of these problems is true?

I also need to know if there are well known/documented fixes towards any of the known problems.

By meits

Scribe (6571)

03-02-2014, 07:44

The part of the pitched audio is very true, but that's fixable for the audio cartridges... I've not seen a sollution for the PSG on this...
You can adapt (at least) msx-music and msx-audio to 7MHz by replacing their crystal. Music will skip some (parts of) notes once in a while, but there won't be any pitch changes. Dunno about SCC and Moonsound stays the same on any frequency.
You can also let the cartridgeslots keep on running on 3.5MHz. That way you don't need to adapt any of your cartridges. I just wonder if the data transfer speed of a mass storage medium will suffer of this.

Because 7MHz needs to be switched off when the VDP is doing stuff, the pitch of the music will never be stable... Unlike the turbo mode on the Panasonic MSX2+ models...

Haven't heard any of the other problems. Someone else might...

By msd

Paragon (1532)

03-02-2014, 08:35

Yes, for soundchips which use the CPU clock , which is a pin on the cartridge bus, the sound will be pitched. You can't replace the crystal, because it has none. What some did was put an crystal in cartridge itself. The problem with this solution is that the register interface with the cpu becomes unsynchronized. The only sound extension having it's own crystal is the Moonsound. It runs at 33Mhz. The cpu clock far to slow for it anyway. So the moonsound works perfectly with 7Mhz.

Some very old hardware extention like mappers, disk controller might not work. But most things just work. It is not like 7.16mhz is that fast for the chips used.

By Daemos

Prophet (2166)

03-02-2014, 09:10

i just wonder. That is a little bit of brainstorming though and unfortunatly I am not deep into digital electronics but.. we all know that sound is (most of the time) played during interupt. So what if there is some way to force the clock back to 3.5 Mhz electrically during interrupt?

By msd

Paragon (1532)

03-02-2014, 09:12

@deames: That will not work.

By msd

Paragon (1532)

03-02-2014, 10:58

I tought about it more, but I think the missing notes is due that the opll and msx-audio registers also are not fast enough for the 7.16mhz out instructions.

By Daemos

Prophet (2166)

03-02-2014, 11:48

Quote:

I tought about it more, but I think the missing notes is due that the opll and msx-audio registers also are not fast enough for the 7.16mhz out instructions.

I read something about that. I believe someone stated the solution on the net somewhere lets see.

Quote:

Clock speed must be lowered when slow peripherals are accessed. For example VDP, soundchips or floppy controller. Since most of these peripherals have in common that they are accessed through I/O ports, a common configuration is to connect Z80's #IORQ signal to one of the input diodes. Also common is to connect a #SLTSL signal that selects diskROM/floppy controller (which is fine since floppy I/O won't speed up anyway). And most people want manual control of the circuit using a switch of some sort. Another option is to connect the cassette motor relay between GND and a diode input. With these signals connected, you're usually done.

this is from a website which I believe is the guy who came up with the brilliant idea to construct the turbo circuit the way it nowadays is.

By Grauw

Ascended (10819)

03-02-2014, 12:03

I’ve had 7MHz in my MSX-es since forever and never looked back. Perfect to speeding up DOS and if you need to get through repetitive sections of games like Metal Gear 2 Solid Snake and SD Snatcher fast. I wouldn’t worry too much about the downsides of 7MHz; there’s a switch so you can always turn it off.

Also there are some variations of 7MHz I think, one where it slows down the VDP access without slowing down the clock speed. Audio is still pitched too high, but at least it doesn’t get distorted. I think I once followed instructions to make a modification to my 7MHz that does that, I think I wired the I/O wait signal to the wait pin in stead of the clock. But not sure, it’s been a very long time ago.

By Daemos

Prophet (2166)

03-02-2014, 14:38

I was reading something about Z80 and I stumbled upon the eZ80 CPU. This unbelievable CPU made by zilog is (if I may believe the specs written by them) 100% compatible with the original Z80 CPU but runs like 4 times as fast because of high internal cpu core efficiency. It can run on speeds up to 33 Mhz. this is like a R800 on steroids.

Anyone ever considered building this baby into a MSX??

By msxegor

Master (183)

03-02-2014, 15:31

Daemos wrote:

I was reading something about Z80 and I stumbled upon the eZ80 CPU.
Anyone ever considered building this baby into a MSX??

Not possible: has internal peripherials mapped to i/o ports 80h and up - will conflict with standard MSX io oprts.

By msd

Paragon (1532)

03-02-2014, 15:43

these internal peripherals can't be disabled?