Software-only OVERCLOCK for LC475, LC575, Quadra 605

[JDW]

Folks,
@Mr. Fahrenheit very kindly alerted me to a very surprising discussion at the other forum which introduces a groundbreaking discovery by Mustermann. Apparently, you can now overclock an LC 475, CC Mystic and other machines by software alone, without even using Spicy O'Clock, from @Kay K.M.Mods (Kero's Mac Mods). Here's a screenshot of the machine compatibility from the installer app:

When you download the software overclocker BIN file (created by Phipli) and then put it on your vintage Mac and use Stuffit Expander to decompress it, the installer app will look like this:

It installs a Control Panel and an Extension:

No mention is made of software compatibility, but most likely it works on System 7.1 through 7.5.5. (I made these screenshots in Basilisk II booted into System 7.5.5.)

Once installed, you can set the clock speed in the Control Panel (which then requires a restart):

There's even a "Custom" selection in the popup menu that allows you to see higher clock frequencies:

If you try a clock speed too high for your Mac and it freezes, just reboot with SHIFT held down to prevent the CP and Ext. from loading. This and more is described in the installer app's README text. So be sure to read that completely before installing it.

It's not clear if VRAM speed is as important as it is when you overclock with Spicy, but I suspect it is. Having a 68040 with full FPU will also impact your performance and probably overclockability too. Heatsinking at high clock speeds is still important.

Another thing that is not clear is how serial ports and SCSI are impacted. In my own testing of Spicy, serial ports stop working when the CPU is overclocked higher than 43.48MHz. (I confirmed serial ports don't work at 43.7MHz when using Spicy.)

DISCLAIMER: I've not tested this software overclocker on my Color Classic Mystic yet (which still has Spicy O'Clock installed).

@Mr. Fahrenheit has tested it though and confirmed it overclocked his CC Mystic to 40MHz. It's not clear if he tested clock speeds higher than that.

The great thing about this solution is that (1) there's nothing to buy to try it, and (2) you just reboot with SHIFT held down if you overclock too high.

Have fun!

P.S. If you find it useful, I recommend sending a word of thanks to Mustermann and Phipli at the other forum, as well as thank Mr. Fahrenheit for his testing and involvement.

 

[Garrett]

As someone who has done the "hardware" overclock on my 475, I also moved a resistor to keep the SCSI controller at 25MHz (R96 to R95 - see photo). Is there any indication whether or not a software overclock would affect SCSI? I have seen file transfers cause lock ups, reportedly caused by SCSI controller instability at higher frequencies.

 

[JDW]

@Garrett
Because I have not yet done the software overclock, and because I don’t own a 475, I’m not equipped to answer your question.

However, I keyword-searched all pages in the other forum’s thread for “SCSI“ and I found the following post from @Bolle :

Overclock LC475/P475/Q605 without soldering or spicy-o-clock

Very interesting, can anyone confirm the "343S0161" vs "343S1135" thing?

68kmla.org

 

[Garth Beagle]

I did some testing with this a little while back and didn't run into any issues using a BlueSCSI v2 off the internal SCSI bus.

I was able to overclock a Quadra 605 with its stock 25MHz CPU and a LC 475 which had already been HW overclocked to 33MHz.

Both ran ok at 40MHz, the highest it’d set to was 43MHz. Anything higher and it just didn’t seem to take the change.

Here’s some CPU benchmarks at various speeds on the Quadra 605.

 

[ClassicHasClass]

The real question is whether this has an impact on service lifetime and/or burns those systems out sooner.

 

[phipli]

I did some testing with this a little while back

Really? The code was only released this month. Have you been doing your own hacks? Could you share your code?

No mention is made of software compatibility, but most likely it works on System 7.1 through 7.5.5. (I made these screenshots in Basilisk II booted into System 7.5.5.)

The control panel is probably 7.5 to 8.1 (and later with a PPC upgrade). I wrote the CP in RealBasic, so I suspect it wont run in 7.1 (probably will with Finder 7.1.3 installed in 7.1 though - that adds most of the things you need - Finder 7.1.3 came with System 7 Pro and 7.1.2 if you're looking for a copy - you'll then need to install AppleScript probably). The Extension will work in any OS that the 475 family machines will run, and the speed could be changed in another OS and then copied over, or you can edit it with ResEdit.

It's not clear if VRAM speed is as important as it is when you overclock with Spicy, but I suspect it is.

This setup should overclock more than the Spicy wrt RAM, ROM and VRAM timings (as well as serial and floppy drive I believe), because the code also changes the number of wait states to the correct level for 40MHz. This isn't possible usually with a 475 or 575.

Another thing that is not clear is how serial ports and SCSI are impacted.

SCSI clock mod to divide by two should be done to ensure best SCSI reliability. What is it... swapping R96 to R95 on the 475? Should already be done on the 575 from factory. Some people seem to have good luck without needing to do this... but if you're going for records, you'll want to do the mod.

My 475 has the upgraded 80MHz clock divider part (88916DW80??), the SCSI clock mod and a 40MHz grade CPU with a heat sink.

I've got a reliable 50MHz at the moment, RAM is likely my limit as the soldered RAM is 80ns. Even at 40MHz with 40MHz timings I should have 70ns RAM, so it is a significant overclock on the soldered RAM. I'm not going to be pushing faster any time soon becaues when I have time I want to get back to improving the software and implement Mustermann's latest tweaks. I've managed to run a CPU benchmark at 55MHz, but it crashed while doing the video benchmark (I only have 70ns VRAM). At 60MHz it crashed instantly.

Is there any indication whether or not a software overclock would affect SCSI?

It physically increases the bus clock, identically to changing the resistors. The benefit is that it can also change the number of wait states to 40MHz settings, so improves the behavior of subsystems that need that (you're using 40MHz timings instead of 25 or 33MHz - the 475 ROM doesn't support 40MHz sadly (unlike the 650). Best to do the SCSI clock speed resistor mod as you've pointed out.

following post from @Bolle

The 161 vs 135 thing isn't to do with SCSI, that is to do with which type of clock generator (the part we're manipulating to change the CPU clock) is fitted. There were two types, at least two part numbers.

The real question is whether this has an impact on service lifetime and/or burns those systems out sooner.

The boards were spec'd to 40MHz at design, as was the chipset for the most part. Things that might struggle at 40 are possibly the 88920, VRAM, RAM and the CPU. There is a resistor connected to the CPU that might need to be set to different values depending on the system clock, but I've never bothered changing it, and wouldn't be confident about the values in the schematic anyway as Apple never shipped 40MHz machines.

 

[JDW]

@phipli
Incredibly informative and helpful post, thank you! And kudos to you on the amazing work you’ve done in bringing Mustermann’s overclocking work to the masses.

 

[Garth Beagle]

Really? The code was only released this month. Have you been doing your own hacks? Could you share your code?

I used your build you'd attached in the comments to your video.