Interesting ! It looks like a OEM Micron motherboard. Cannot find anything...

For the time that would of been an incredibly expensive board. So strange there is nothing about it.

As a progress update I have now managed to get cache and various other elements functional.
Also disk controller enumeration etc is working.
I'm now using an AOpen DP5 motherboards BIOS which has been adapted to run on this board.
Some chipset logic configuration is still required however with the documentation at hand it's going somewhat ok.
The next trick will be to get the board to consistently set the masked [7:6] bit chipset registers init values for 52h.
Currently I am using a reset quirk of the chipset to set those bits (essentially bug programming).
Essentially when cold posting the board the cache register is programmed with incorrect cache configuration parameters for the AOpen platform and as a result cache is not configured correctly.
So what I do is post, then I remove the cache config jumper, (bit 6 high) and then reset and I get the inverted logic sampled and bits 7:6 are configured as 10.

As you can see this has given good results 😁

Nice work - must have cost a landslide back then.

No pictures this time, but finally I can report I have managed to restore full speed and full cache functionality using a custom crafted AwardBIOS 4.50PG adapted from the AOpen DP5. Itself yet another undocumented unseen dual pentium motherboard.

Will post more once I have the time and a proper PCI IDE card haha. PXEBooting a P586 architecture via iSCSI over gigabit is a bit of an alice in wonderland adventure worthy of it's own thread. 🤣
Next up will also be modding the board with a stronger VRM and getting higher multipliers, plus syncing the APIC for fast dual processors.

And just for fun let me give the laundry list of faults this board had:

1. Both 3.3V Linear LDO voltage regulators for CPU Vcore had failed (likely cooked to death), the heatsinks on them are pathetic.
2. 430NX had loose pins on two sides (bad terrible solder)
3. S82379 SIO had loose pins on bottom edge.
4. Keyboard rom socket had a spider nest under it and corroded pins.
5. One of the 433 LBX chips had loose pins all around. (yet again crap solder)
6. two address lines of BIOS chip were cut
7. 1 CPU address pin on primary socket had a bad corroded joint.
8. 2 ISA address and 2 ISA data lines on back were scratched through
9. AT header power pins had cold joints (reflowed)
10. Original BIOS is corrupted and will more often not post than post, large part of chipset setup logic is FUBAR
11. degraded SMD capacitor on Address Line 30 (used for strapping cache config after PWR-OK edge) was causing cache config flipping between 256/512K.

So as an update. It turned out that the cache I originally though working was a fluke. A bunch of chips and the buffers for them were degraded.

A while ago I actually went about testing the cacheless wonder. Well here are some more images.
When did you ever see Vintage Edition CPU-z with the Socket Dropdown active? 😜

Windows 2000 installed (without L2 cache active) -oh horror
The memory subsystem performance was astonishingly dreadful.
After some testing done using a custom build of the chipsandcheese memory latency tool we came to suspect the reason for this is that the OS partly uses the L2 cache to speed up page table lookups.
Without this, memory address generation and lookups quickly become absolutely dreadful beyond about the 256KB size.
Here is a cache enabled 430TX compared using a somewhat different processor.

The memory latency here shockingly is worse than the worst Nvidia GPU OpenCL could still be run on in 2021.
For a GPU to outperform a CPU's memory latency in any way is pretty hefty.

Anyways, I've finally received some new cache chips for this thing today, finding 3.3V Supply Low Voltage TTL rated SRAM is a PAIN.

Next modifications that are about due:

- Already modified BIOS for very low AT and PCI clk ratios
- Replace all the slow 74F244/245/373 series logic chips with ultra fast 74ABT series. (MOAR MHZ!!!)
- Replace the crystal oscillator can driven FSB with a custom PLL PCB and inject any desired FSB frequency.
- Wire all the multiplier options from the socket to an addon switchblock.
- Split the 3.3V Voltage plane at the sockets and install a custom VRM PCB ontop of the linear Vreg 3 pin footprint via headers. (Pentium MMX SMP!)
- Design a new cache interface PCB that goes ontop of the existing async SRAM sockets but allows the use of a single 512K Pipeline Burst SRAM chip. (512K is the max 430NX supports)
- Attempt 100MHZ FSB speedrun

Hello and congratulations on the work and the motherboard.
I have seen the excellent work done, to adapt the BIOS, and to improve the performance, I guess the voltage regulators are linear, in that case going up the frequency would have more heat to dissipate, so I would recommend 166MHz. Perhaps we can go further, but to produce less heat it would be necessary to use cpu for laptops with reduced voltage, this should guarantee operation at lower temperatures and therefore greater reliability, these are ideas that I made myself (maybe am I wrong?). In several VXs with linear regulators I have had problems with 200 or 233MHz CPUs, perhaps changing the heatsink on the mosfets (with a bigger one) and adding a fan would work better.
On a VX and a TX with switching regulators, on the other hand I don't have these problems, and I have AMD K6-2 CPUs at 360 and 400 MHz, the limit is due to the FSB that reaches 83MHz at the maximum, but since you want to reach 100, maybe it would be possible that it works more stable if you used a 90MHz FSB, especially if you can make (divider 1/3) that the PCI goes to 30Mhz, instead of 45MHz with divider 1/2.
With fsb 90 a 233MMX would go at 315Mhz, and it would be a very good frequency for that CPU, then having two would be even better, but reaching and exceeding 300 is possible, but it is not guaranteed that it will be stable and reliable over time.

I will gladly follow the developments of your work, I am very interested in this thing of the FSB 100, in my opinion those who have tried have failed because the divider 1/2 makes the PCI work at 50MHz.

After much toil and suffering I have a new update.
L2 cache is working again FINALLY!!

Here is proof of that alongside a quick test of aida64 version 2.50.

Now that this is all working I can actually start optimization work alongside getting this bios code tweaked to the max potential.

Time for the real stuff!

I've gotten the latest Linux Kernel booted and running on this thing.

So how much storage does your pentium 1 have?

Ah yeah a casual 1TB disk, nothing much...

Just realized I never actually posted a picture of my custom BIOS for this board.

So here you are:

Sorry to bump old thread

I came across this thread trying to identify a board I recently picked up, which appears to be the single cpu version of this board. https://theretroweb.com/motherboards/s/sprint … f.-co-mb-p5n-sp

It looks like you have got the board functional with your bios witchery, I have dumped the bios for my board it may be of use, not sure if it would be the same bios being the single CPU version. Interestingly it says "Evaluation Rom - not for sale" I wonder why; perhaps my board some kind of pre release revision?

After reading your findings regarding loose pins on the solder joints I had a close look and also have identified a loose pin on one of the 430nx chips so thanks for pointing that out, I agree the board has (bad terrible solder). I will carry out repairs at some stage when I have the time

Bios dump
https://drive.google.com/drive/folders/11YoTM … aDm?usp=sharing

Wow this is pretty amazing!

I'm surprised that it is an Award BIOS and not AMI like mine originally was.
What chip does yours use for the SIO?

Is it S82378 or S82379 ?

It would be great if you could post some high quality images of the board, then I can add them to TheretroWeb.

The chip is S82378ZB

Just an update on my experience with the board since posting

I re-soldered the pin i found disconnected on the S82433NX closest the cpu socket and found the chip was running extremely hot. After inspecting the S82433NX data sheet I discovered pin 150 which was disconnected should be tied to 3.3 volts however the motherboard trace is tied to 5 volts. I disconnected the pin and the chip now runs at normal temperature (the pin is tied to the other 3.3 volt pins internally so it works fine). It seems the pin was disconnected intentionally as sprint made a mistake when designing board.

I have found the board freezes constantly trying to run windows 95. I have tried EVERYTHING. Removed L2 cache and disabled, stuffed around with every bios setting, tried various IDE controllers/ video cards, different ram. Windows just freezes at random points. And also corrupts data on the hard drive. I have monitored cpu voltage it drops to 3.194 volts which I wouldn’t have thought would be enough to cause such problems but i don’t know. I replaced the 2 capacitors filtering the 3.3volt mosfet output also. Replaced both 66mhz and 14.318mhz crystals. Ive tried windows 95a and windows 95c. The board doesn’t appear to freeze in DOS and runs through all benchmarks/ cache tests etc from phils benchmark pack. However I haven’t pushed system as much as i would on windows 95 reading/ writing data etc. I cant figure it out I think the S82433NX is possibly partially damaged due to feeding it 5 volts but I have no idea 🙁

s.mouse wrote on 2022-08-30, 04:26:

Sorry to bump old thread […]
Show full quote

Sorry to bump old thread

I came across this thread trying to identify a board I recently picked up, which appears to be the single cpu version of this board. https://theretroweb.com/motherboards/s/sprint … f.-co-mb-p5n-sp

It looks like you have got the board functional with your bios witchery, I have dumped the bios for my board it may be of use, not sure if it would be the same bios being the single CPU version. Interestingly it says "Evaluation Rom - not for sale" I wonder why; perhaps my board some kind of pre release revision?

After reading your findings regarding loose pins on the solder joints I had a close look and also have identified a loose pin on one of the 430nx chips so thanks for pointing that out, I agree the board has (bad terrible solder). I will carry out repairs at some stage when I have the time

image3.jpeg
image4.jpeg
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image6.jpeg

Bios dump
https://drive.google.com/drive/folders/11YoTM … aDm?usp=sharing

Hey, it's been a long time since I responded. But would it be possible for you to upload higher resolution images for TheRetroWeb project?
I've already added the low resolution ones from you
https://theretroweb.com/motherboards/s/sprint … f.-co-mb-p5n-sp

If you'd like you can also join the RetroWeb discord (link on the website footer).
And we can help you get this board fixed.