Techknight™ - SE/30 Over Clocking

[uniserver]

Because of all this talk about disabling the onboard video, and just running the Greyscale out of the IIsi video card, into the CRT.

This should mean that we could be open to 20mhz or even 25mhz free speed boost.

Hopefully as techknight makes progress with the Greyscale, maybe he will get around to pulling out that 31.33440mhz oscillator and maybe installing a 40mhz or 50mhz oscillator.

 

[techknight]

I dont have any oscillators.

 

[uniserver]

i am gonna get some… from somewhere… when i do… hopefully an assortment for a low price… --- should be able to send you some!

 

[olePigeon]

I can check my local surplus. They have a whole section for just clocks and crystals.

 

[tsillay]

I've got a 32,40 and 50mhz arriving today.

Also just discovered silicon oscillators, which are programmable. If I could find a 5volt version I'll go that way.

Check my comments on the greyscale thread regarding the relationship between the vsync clock and the CRT hi voltage... Over clocking could easily kill the analog board..

 

[tsillay]

Unbelievably, it almost works. Using a 40mhz xtaI. I didn't expect scsi or adb to fly. (20mhz bus)

No mouse. Kbd ok. Rcpii ok. Sound is up an octave or so.

It boots hellish quick!!

I've got a 33mhz 030 and 882 on the way .

 

[olePigeon]

OK, my local supply store has boxes and boxes and boxes of crystals in many different shapes, from the full size can to SMD versions, in all manner of frequencies.

So if anyone needs any, let me know, I can pick them up on my way home from work.

[attachment=0]osc.JPG[/attachment]

 

[uniserver]

Unbelievably, it almost works. Using a 40mhz xtaI. I didn't expect scsi or adb to fly. (20mhz bus)No mouse. Kbd ok. Rcpii ok. Sound is up an octave or so.

It boots hellish quick!!

I've got a 33mhz 030 and 882 on the way .

LOL!

so to re-cap, SE/30 @ 20mhz /w a 40 mhz oscilator

- no mouse

( so far )?

but all else seems to work? video and scsi.. or does the IIsi video card need to be used ?

please feel free to give us more details, as you are doing something that i believe nobody has ever done before

 

[tsillay]

I've disabled onboard video by pulling ue7. This kills video Rom/ram addressing and video sync to crt

So.

Se30. IISI Rom. 20mb ram. System 755. Rcpiisi video at 640x480.

Softpivot drivers and control panel don't load so using 'monitors' ctrl panel.

40mhz can xtal. 16mhz 030 and 882.

It's not stable enough for primetime yet.

I'll get to the bottom of the mouse issue. I didn't expect adb to work at all!!

 

[uniserver]

so we could just do what zackl is doing… if all else fails…

pull the CRT, install, 9/10" LCD and drive it with RPII Card

maybe clock it up to 20-25mhz load it up with 128megs ram.

Dougg3 rom… Floppy Emu, SCSI2SD etc… and have like a SUPER MAC SE/x

 

[tsillay]

A bit of an update on work to date.

To summarise, replacing the 31ish mhz xtal with a 40mhz xtal kind of works, but no ADB mouse, and there's a fairly predictable bus error after 20 mins of operation after which the machine won't warm boot (it needs a power cycle to come back)

I scored a 40 mhz 030 and 882 off ebay to see if the limitation was the frequency rating of these parts. Swapping the 030 is simple on a socketed motherboard.

Swapping the 882 takes a bit more work. You cut the chipselect trace on the mobo (runs from the GLUE to the CoPro underneath the board). Put a pullup resistor on the 882 to disable it.

Then route the CS line to pin 2 on the PDS connector. This line is unused on the SE30.

Put the 40mhz 882 in the Radius CP card.

This combo works just fine with the 31 mhz xtal, but sadly there is no improvement in the stability when a 40mhz xtal is used. In fact it's probably worse!

So it's back to the drawing board, it appears that something else on the MOBO doesn't like being overclocked.

Next step is to separate the clocks out, feed the VIAs from a lower freq clock and see if it can deal with the waitstates.

I also want to build an oscillator circuit that can be adjusted, and try stepping it up from 32-40 mhz and see where problems start occuring.

Tim

 

[Trash80toHP_Mini]

Could you be overloading the line driving capabilities of the SE/30' 68030->68882 by using the Co-Pro installed on the VidCard? I'll check the IIsi schematic later, but I'll bet there are line driver ICs in between the CPU and PDS for the CoPro on the IIsi board that are lacking on the SE/30 MoBo for obvious reasons. Totally removing rather than disabling, or better yet, replacing the CoPro outright would be likely be optimal.

 

[Trash80toHP_Mini]

I haven't been able to figure it out from the schematics, my brain doesn't do EE type stuff well at all.

However, hotwiring a line driver IC into your CoPro CS jumper to n.c. pin 2 on the PDS might be something that could help. If it's n.c. and you're going straight from CoPro CS on the MoBo to the PDS pin, I'd guess that could be problematic, even if it appears to work correctly without the extra oomph.

 

[Trash80toHP_Mini]

I've disabled onboard video by pulling ue7. This kills video Rom/ram addressing and video sync to crt

That sounds like the silver bullet for putting onboard video down hard. @techknight whatcha think about this in terms of the register loading issue that merely pulling the Video ROM might not accomplish?

This is a very specific necro post (I have zero problems with pulling old threads back to the surface, but some seem to?) best made in this context.

If it's better to clean this info up this scattershot research in a new thread:

 

[Franklinstein]

Meh, I don't see a problem with necros if they're relevant. There are plenty of new threads around with topics that have already been discussed. There seems to be some contradiction at times: you'll get people who say, "Have you searched?" when a new thread is posted about something common, and occasionally those same people will complain about a relevant necro post. Make up your minds!

Anyway the SE/30 has many clocks that are tightly coupled. This was likely done both as a cost saver and to simplify the design, as it was in many computers which based their timings off of the NTSC color clock frequency of 3.579545 MHz. I guess a few relevant clocks haven't been fully teased out yet. Also, I don't think you'll find many PDS cards that will play nicely with an overclocked logic board: more than 20-25MHz and you'll probably start to see problems crop up. The CPU accelerators get away with highly-clocked CPUs because they decouple them from the rest of the logic board, which is why performance is often mediocre unless your accelerator also includes an L2 cache of some sort to make up for the still-slow main memory, and any attached PDS cards still operate at their original speeds.