Wombat (650, 800) board overclocking limitations

[eharmon]

Oh using the jumper that way is very cute. I'll probably give that a go next time my board is out to add some flexibility and easily swap between stock and whatever customized configs I have in the other configuration.

For now I've been hacking the LC 475 ROM directly to futz with even more customizing timings. A few discoveries:

1) Booting the machine with (non-bump) 40MHz timings seems to pull RAM performance down by 11-13%, per Norton SysInfo. Overall system performance is about the same otherwise. Not the worst impact, and really isn't bad for a 21% clock increase.
2) The LC 475 ROM doesn't seem to have the bump config tables at all, only the regular configs, or at least not in the same places. Which might explain why it applies non-bump (faster) timings than a stock ROM would on 80ns machines (C650/Q650). So simply swapping in the LC 475 ROM serves as a minor overclock for memory.
2) The custom ROM I'm using has 55ns chips, which means you can push the ROM Speed a little, even at faster clocks. Lower is better. Stock Q800 runs at a speed of 3, stock Q650 at 4, and the respective 40MHz configs at 4 and 5. Even running at 44MHz I can push that down to 2 and, presumably, get faster ROM reads, so toolbox calls should run faster. At 1 the machine gets very unstable, and I'm guessing at 50MHz you're gonna need 3+, even with fast ROM chips. But that adds another dimension to overclocking. Not sure there's any ROM read test out there, might be worth creating to benchmark/verify checksums to ensure it's running stable.

 

[eharmon]

Oh and something very low level in 8.1 haaaaaaaates clocks over 42Mhz or so, even with the updated memory timings. I need to dig through in MacsBug but it seems like it's waiting on hardware that never answers back (no longer ignores non-functional serial?)

 

[Phipli]

I've been messing with a Q800 board at 50MHz using the 40MHz timings in the ROM.

I'm having the same issues where about half the time it just stops booting, but the mouse still moves.

It is extremely sensitive to RAM selection. It isn't entirely down to outright speed as a 50ns 8MB SIMM won't work, but some 60ns SIMMs do.

It doesn't like if I add multiple SIMMs, even if it is happy with both individually. I might remove the remaining onboard RAM.

Regarding RAM timings, it does feel like the 40MHz ones are either a bit beta, or they hit the limits of the hardware somewhere. Has anyone compare the timings to those in the 840av ROM (same ROM used in the 660av)?

This machine has a ROM slot fitted, so is more open to experimentstion.

 

[Joopmac]

Hello guys
Awesome thread
I have some 650/800 boards spare, at 33Mhz stock
I would like to mod these to 40Mhz
Unfortunaly i am a bit confused, can I please ask for a little help?

Is all i need to do for 40Mhz:


- replace oscillator with 20Mhz one
- add 300R resistor to R151 if not there
- add 300R resistor to R152
- change existing 1.2K resistor to 1.5K at R152
- add jumper or 0 ohm resistor to the spot between R148 and R233

 

[Fizzbinn]

2. My Daystar 128K Quad Cache (aka FastCache Quadra) does not work in the overclocked configuration. The Daystar QuadControl v2.3 init hangs at startup. Unlike the IIci cache card, the Quad Cache card is not enabled until the software kicks in.

I seem to be hitting the jack pot on 68k L2 cache in that I think I picked up one of these Daystar "FastCache Quadra" L2 modules for cheap on eBay (after also finding one for the IIsi).



Any pointers to the QuadControl v2.3 extension download? I don't see it on Macintosh Garden.

It's labelled 33Mhz but I'm hoping that is just an upper limit as I'd like to use it in my 25 MhzQuadra 700.

 

[eharmon]

I seem to be hitting the jack pot on 68k L2 cache in that I think I picked up one of these Daystar "FastCache Quadra" L2 modules for cheap on eBay (after also finding one for the IIsi).

View attachment 74289View attachment 74290

Any pointers to the QuadControl v2.3 extension download? I don't see it on Macintosh Garden.

It's labelled 33Mhz but I'm hoping that is just an upper limit as I'd like to use it in my 25 MhzQuadra 700.

How did you find that, I've had a bunch of alerts and never saw it, so I'm envious.

Yes it should be fine to run it at 25MHz.

The software should be optional (it should Just Work™) but offers some other nice (somewhat unrelated) features. You can still download it from DayStar, or at least whoever maintains their archive: https://daystartechnology.com/files/d_software_download1_xeemdfzgntze6rvusnn52z.html

It's mislabeled as "Quad040" but it applies to many 040 products, the Cache included.

You'll probably have to Save As that file, as it incorrectly downloads as plain text in the browser, otherwise.

 

[Fizzbinn]

How did you find that, I've had a bunch of alerts and never saw it, so I'm envious.

Yes it should be fine to run it at 25MHz.

The software should be optional (it should Just Work™) but offers some other nice (somewhat unrelated) features. You can still download it from DayStar, or at least whoever maintains their archive: https://daystartechnology.com/files/d_software_download1_xeemdfzgntze6rvusnn52z.html

It's mislabeled as "Quad040" but it applies to many 040 products, the Cache included.

You'll probably have to Save As that file, as it incorrectly downloads as plain text in the browser, otherwise.

It just came up when I manually checked an eBay saved search for "Daystar Digital", listed as "daystar digital 105013-109 33 Mhz Card 01-FC040-001". Super lucky timing I suppose as I'm sure lots of people have saved searches/alerts set up.

Thanks for the tips/pointers!

 

[Joopmac]

Does anybody know if the mod at page 10 with the r151 installed is for 33/40 or 20/25mhz rom timing? I’m confused because all my boards have r151 already installed (q650-800) and they run at 33 not 25mhz

 

[Mustermann]

There are so many great information in this threat!
But one thing I was not able to understand:
What are the flags

fastwr
drpchg
drpw
cyc2ta
dwcpw
drcpw

in djMEMC Configuration Register exactly doing?

I already found;

ROMspeed n add n waitstaits to ROM access
mhz33 add one waitstait to RAM access

@Bolle mentioned here: https://68kmla.org/bb/index.php?threads/lc-475-project-upgrades-mods.47687/page-2

.... the values that we know from the memory controller datasheet ....

Anyone know where to find this information?

 

[Arbee]

Don't ask, because I'm not telling

 

[Mustermann]

Thank you so much.

 

[RandomDamage]

Hi all - I've been playing around with hacking the ROM in a Centris 610 to get it to work reliably at 40MHz. Using the info from this thread and https://github.com/cy384/wombat-hacks, I've been able to force it to use the DRAM 40MHz timings just fine. What I haven't been able to quite figure out yet is how to adjust the DAFB frame buffer timings. (The system is stable at 40MHz and 256 colors at 832x624, but if I try to use 16-bit color, I get artifacts even with 70ns VRAM installed in the slots - though the onboard VRAM is only 80ns) I'd like to confirm if my ROM DAFB initialization modifications are actually doing anything. I tried modifying the ultra-wombat-hax-tool to dump out 0xF9800010, but for some reason I get an illegal instruction error. (The ultra-wombat-hax-tool works just fine, unmodified). Trying to read the address in MacsBug gives me some weird results with differering data if I do byte, word, or long reads. Anyone have any tips on how to reliably read this address?

 

[jmacz]

Getting around to over clocking my Q800 but only going to go to 40MHz.

I couldn’t tell what the conclusion was but at 40MHz, is the preferred approach to leave the gestalt ID alone or is it to change the gestalt ID to 59 (by removing r151 and r152) to utilize the unreleased 40MHz timings? Difference seems to be ~1% (faster with leaving the gestalt ID alone) but wondering if there’s any advantages to the 40Mhz timings if I am stopping at 40Mhz?

Also with the gestalt ID changed to 59, what is the system recognized as? Is it still a Quadra 800 or would it some form of “Unknown”?

Lastly is the stock heat sink with the 68040/33 ok or do I need to upgrade the heat sink with a fan?

 

[eharmon]

Getting around to over clocking my Q800 but only going to go to 40MHz.

I couldn’t tell what the conclusion was but at 40MHz, is the preferred approach to leave the gestalt ID alone or is it to change the gestalt ID to 59 (by removing r151 and r152) to utilize the unreleased 40MHz timings? Difference seems to be ~1% (faster with leaving the gestalt ID alone) but wondering if there’s any advantages to the 40Mhz timings if I am stopping at 40Mhz?

Also with the gestalt ID changed to 59, what is the system recognized as? Is it still a Quadra 800 or would it some form of “Unknown”?

Lastly is the stock heat sink with the 68040/33 ok or do I need to upgrade the heat sink with a fan?

If you have a flashable ROM and a socket, the best option if you want to change it is flashing a ROM with 40MHz timings for the Q800. No weirdness with the gestalt ID and fully reversible without getting out the soldering iron again. That's my 2 cents anyway.

They do seem to run alright at 33MHz timings, but I found my system more stable in general at 40MHz timings. Especially the 800 which has tighter timings at 33MHz than the 650s (though with faster onboard memory to match). Subjective results though, I'm crashing the OS myself 90% of the time.

Interestingly you can leave the ROM timings as tight as they'll go with the flashable ROMs as they're pretty low latency, even at high clock speeds. However, if you just run QuadControl to copy ROM to RAM you'll get the same boost (if not more) (https://68kmla.org/bb/index.php?threads/rom-in-ram-for-quadra-performance-boost.46536/).

In total: from my experience the 40MHz timings seem more stable, especially on a Q800. But you might just try it out with 33MHz and see if you're stable without switching it over. If you're happy with it, it's probably fine.

For heat, I run a block-shaped heat sink (not those crown ones found in later Quadras) with a small fan on top. Probably overkill for later masks, but recommended or even required for D masks. My machine has an E31F. I've practically been spamming this link lately (sorry), but it comes in handy again...E+ masks run coolest: https://eharmon.net/retro/macintosh/motorola-processors/

 

[jmacz]

@Phipli is this graphic correct? It says without R151 = 20/25MHz but this seems to contradict the archived clock chipping page. And when I look at my Q800 board, it has R151 removed stock (and it's running at 33MHz).

 

[jmacz]

If you have a flashable ROM and a socket, the best option if you want to change it is flashing a ROM with 40MHz timings for the Q800. No weirdness with the gestalt ID and fully reversible without getting out the soldering iron again. That's my 2 cents anyway.

I have an extra ROM slot sitting around (bought an extra when I purchased a replacement for my SE/30) and can add that to the Q800 logic board. But I think I read a blog from @dougg3 that showed that the ROM SIMMs need to be tweaked to be fully compatible with the Quadras. I haven't come across Quadra specific programmable ROMs yet (never looked before) so will need to search for that.

They do seem to run alright at 33MHz timings, but I found my system more stable in general at 40MHz timings. Especially the 800 which has tighter timings at 33MHz than the 650s (though with faster onboard memory to match). Subjective results though, I'm crashing the OS myself 90% of the time.

Did you end up using Apple's gestalt 59 40MHz timings or did you tweak them further?

I took a look at @cy384's GitHub page but didn't notice a pre-built ROM binary with just the timings change. I guess I'll need to use his tools to create one.

For heat, I run a block-shaped heat sink (not those crown ones found in later Quadras) with a small fan on top. Probably overkill for later masks, but recommended or even required for D masks. My machine has an E31F. I've practically been spamming this link lately (sorry), but it comes in handy again...E+ masks run coolest: https://eharmon.net/retro/macintosh/motorola-processors/

I'll have to remove the stock heatsink to see which CPU I have. For the replacement heatsink you used, does it use the stock clamps or was it the type that uses heat transfer double side tape? You don't by chance have a link to the one you used do you?

 

[jmacz]

But I think I read a blog from @dougg3 that showed that the ROM SIMMs need to be tweaked to be fully compatible with the Quadras. I haven't come across Quadra specific programmable ROMs yet (never looked before) so will need to search for that.

Nevermind. Found this.

ROM hacking in the 68040 Macs

As some people here already know, I have spent the last couple of months getting to know the Quadra (1MB) ROMs better and get a ROM disk working for it. The basic idea was simply "if we can have a ROM disk for the SE/30, why not for my Q900?". I started by reading up on Rob Braun's excellent...

68kmla.org

Will look into obtaining one.

 

[jmacz]

For heat, I run a block-shaped heat sink (not those crown ones found in later Quadras) with a small fan on top. Probably overkill for later masks, but recommended or even required for D masks. My machine has an E31F. I've practically been spamming this link lately (sorry), but it comes in handy again...E+ masks run coolest: https://eharmon.net/retro/macintosh/motorola-processors/

So mine is an XC68040RC33M with a mask of 2E31F which is the same as yours.

Let me know which heatsink you ended up going with.

I'm looking at @zigzagjoe's thread on this: https://68kmla.org/bb/index.php?threads/68040-heatsink-options.45824/

I will probably use the stock heat sink and then pick up a 40mm fan and then figure out how to mount it... not sure if I want to screw it into the stock heatsink fins so will probably 3D print (carbon fiber high temp filament) some type of mounting bracket. But there's not much room within the Q800 case. With the stock heat sink on there, I have almost exactly 10mm between the top of the fins and the plastic chassis, and that's without thermal paste on there yet. Hmm..

 

[dougg3]

Nevermind. Found this.

ROM hacking in the 68040 Macs

As some people here already know, I have spent the last couple of months getting to know the Quadra (1MB) ROMs better and get a ROM disk working for it. The basic idea was simply "if we can have a ROM disk for the SE/30, why not for my Q900?". I started by reading up on Rob Braun's excellent...

68kmla.org

Will look into obtaining one

Yeah, I was going to point out the CayMac SIMM. I think I've heard of someone else making something compatible as well, but I can't remember. To be fair, I think people have found that older SIMM designs happen to work in the 610/650 despite not disabling the onboard ROMs like the newer design can do, but it's probably more likely to damage something, so I'd definitely recommend getting one with the correct design if you can.

 

[eharmon]

I have an extra ROM slot sitting around (bought an extra when I purchased a replacement for my SE/30) and can add that to the Q800 logic board. But I think I read a blog from @dougg3 that showed that the ROM SIMMs need to be tweaked to be fully compatible with the Quadras. I haven't come across Quadra specific programmable ROMs yet (never looked before) so will need to search for that.



Did you end up using Apple's gestalt 59 40MHz timings or did you tweak them further?

I took a look at @cy384's GitHub page but didn't notice a pre-built ROM binary with just the timings change. I guess I'll need to use his tools to create one.



I'll have to remove the stock heatsink to see which CPU I have. For the replacement heatsink you used, does it use the stock clamps or was it the type that uses heat transfer double side tape? You don't by chance have a link to the one you used do you?

Yeah CayMac is good to use, as you found.

I used the identical gestalt 59 timings, yeah, just spun a ROM hack myself. I did tweak the ROM speed to minimum wait states (25MHz config) since that works fine with modern flash ROM SIMMs, as noted above.

So mine is an XC68040RC33M with a mask of 2E31F which is the same as yours.

Let me know which heatsink you ended up going with.

I'm looking at @zigzagjoe's thread on this: https://68kmla.org/bb/index.php?threads/68040-heatsink-options.45824/

I will probably use the stock heat sink and then pick up a 40mm fan and then figure out how to mount it... not sure if I want to screw it into the stock heatsink fins so will probably 3D print (carbon fiber high temp filament) some type of mounting bracket. But there's not much room within the Q800 case. With the stock heat sink on there, I have almost exactly 10mm between the top of the fins and the plastic chassis, and that's without thermal paste on there yet. Hmm..

The heat sink I have is the one that comes off a 700, 900, or early 650, with the stock clamp matching that sink. It was designed for the D masks which generate more heat. Since the later masks were cooler I assume the "crown" style sinks were introduced as a cost cutting measure.

They're also (iirc) a bit lower profile than the crowns so a low profile fan fits. I have a Noctua NF-A4x10 FLX. With the 700 heat sink the screws actually grip in between the fins, no drilling needed (though it does leave a little scoring behind).

Any 'ol stick on sink will work too, but the clamp ones are nice because you can avoid thermal epoxy leaving them removable.