Xinetron X/LAN Xi-386/486-SC rev.A based on Xinetron X/LAN Xi-210-B also known as USA SC-9204-A
A riddle of motherboard.

A powerful looking 386/486 hybrid assembly:
- plenty of CPU/FPU sockets
- the two VLB slots are especially interesting
- two extra level2 cache chips sockets suggest write-back capabilities
- CAN-4 crystal oscillator socket makes it easy for overclocking
- limited number of jumpers is always a plus
- an unknown (to me at least) X/LAN chipset - what can it do?
While my expectations were high, the board came hard dead - plenty of damage in the upper left corner from an old battery leak.
Repaired corroded rails on both sides, replaced elements and sockets, replaced keyboard controller and connector. Scrub.
Monitor eventually lit up, much to my satisfaction after long period of iterative fixes.
The board came with Intel 486DX-33 CPU, 32Mb 70ns rated RAM (8x4Mb) and 20ns rated 128Kb L2 cache.
After confirming the system's basic functionality with the existing setup, my curiosity turned to exploring the full potential of the 386 hardware paths it offered.
This motherboard is not documented anywhere so took a moment to figure out what the few jumpers do.
JP1 (486SX/DX) is obvious.
JP12 (NPX IN/OUT) does not make any difference.
JP13 (486-50IN) does not make any difference.
JP20 (U42 Disable) does not make any difference.
JP21 (386) is obvious. Must be closed for 386 processors and open for 486 ones.
JP17 (VESA) is obvious. VLB wait states. Didn't explore them. Notes below.
EDIT
About the chipset - a post i made a while ago in the old hardware giveaway thread shows a motherboard that is almost identical to this one here. The main CI on it is "USA integrations" instead of Xinetron X/LAN. Quick search in TheRetroWeb for motherboards based on "USA i" chipset revealed this 3 boards of the same design. One of them had the entire manual scanned.
Xinetron X/LAN Xi-210-B is relabeled USA Integration SC-9204-A
/EDIT
Plugged a 386DX-40 processor, closed JP21, inserted Trident 8900C ISA video card, standard IDE controller with CF card, 80MHz crystal oscillator.
Default BIOS settings.
Lights on, everything seems to work.
It is worth mentioning that there is a discrepancy in how the base frequency is derived from the crystal oscillator - it is divided by 2 for 386 processors and used as is for 486 ones. First time seeing this kind of setup.
Naturally the first thing i wanted to try was to see how VLB graphics cards work with 386 processors.
This quickly went nowhere.
I usually start with Ark1000VL and S3 Trio64 based adapters but both of them didn't produce an image this time. The speaker started beeping some sequence upon power on which indicated that not all is well. Fetched few more cards from the stash to test with. Still no go. Eventually tried pretty much each and every card from this extensive list. With the exception of ATI Match32 and Cirrus Logic GD-5428 cards none of the rest worked. Even the two that produced a picture made the system very unstable.
Switched to 486 CPU to see how that goes - everything just worked out.
Story was the same for VLB IDE/EIDE controllers. Didn't check VLB SCSI ones.
So, it looks like this board has some major integration issues with 386 processors and VLB cards.
Ok, fine. Had to step down to ISA extension cards.
Started with Cirrus Logic GD-5434. Didn't go well - no video signal.
Tried ET4000AX and W32i - no video signal or highly unstable.
Finally, a Cirrus Logic GD-5428 based card (Diamond SpeedStar Pro) enabled the system to operate stably.
Tested several more adapters - turns out that anything faster than 5428 is a no-go. At the same time all Trident and older models Cirrus Logic cards, as well as Headland/G2, OTI, etc., worked fine.
This is not related to jumper and BIOS settings but is prevalent.
Ok, CL GD-5428 will be used for testing going forward.
Standard ISA IDE controller worked right away already.
Next up - level 2 cache setup.
The board came preconfigured with 128Kb single bank 4x32Kb 20ns and 1x16Kb 15ns. That's ok but 256Kb buffer is strongly preferred.
That didn't go anywhere either.
Populated the sockets with trusted 9x32Kb chips.
There are 5 jumpers to configure the level 2 cache.
Spent good amount of time testing all possible configurations.
Varied the TAG chip - 16/32kb - just in case.
Multiple passes with different set of chips.
No and no.
Tried with 486 CPU hoping for a VLB cards -like pattern. Not this time.
It is safe to say that no stone was left unturned, so with decently high level of confidence i can say that the board does not support 256Kb level 2 cache.
Set things back to the original settings for 128Kb buffer size but replaced the slow 20ns chips with trusted 15/12 ns rated ones.
EDIT
From the found above scanned manual i confirmed the jumper configuration required for 256Kb level 2 cache.
After quite a bit of musical chairs with bunch of chips finally managed to get a working set. My previous attempts failed because the board is quite picky and requires specific chips in specific sockets, does not just take any chips anywhere. This combined with me guessing the jumpers config prevented me from succeeding.
Moving to 128Kb to 256Kb level 2 cache resulted in minor performance improvement only.
/EDIT
At the same time populating the two WB cache sockets worked instantly and improved performance by few percents.
16Mb (4x4Mb) 60ns rated RAM.
Cyrix FasMath 40MHz rated FPU (black top).
BIOS is decently advanced but within the 386 standards. Offers about 10 parameters for L2 cache / memory wait states, ISA bus frequency divider, memory remapping, shadowing, etc. The usual stuff.
--- IBM BL3 at 96MHz (2x48), ISA at 12MHz
Complete stability in Windows required to step down to 90/45MHz.
All BIOS settings on max except:
CACHE READ WAIT STATES = 1 W/S (best is 0)
BUS FREQUENCY SELECT = CLKIN/4 (best is /3)
Board is picky about RAM - requires good 60ns rated chips or system is unstable.
There is something weird with the level 1 cache support of the BL3 processor.
First clue is a discrepancy between what SpeedSys and CCT report.
Notice how SpeedSys does not show the expected higher throughput from level 1 cache but flat lines for the entire level 2 cache range.
At the same time CCT shows the peak.

EDIT: Forgot to retake the CCT screenshot with working 256Kb level 2 cache.

This seems to be the reason for low test results from PC Player Benchmark (4.1 fps), Doom (7 fps - ouch), Quake 1 (2.1 fps), WinTune2 (~1000 KPixel/sec). Some of these are worse than bare 386DX running at 40MHz.
REVTO486.SYS hangs no matter what but LIGHT486.SYS seems to be working. This is unusual.
Not sure what to think about this but the BL3 support is clearly lacking.
--- Cyrix 486SXL2 at 45MHz (1x45), ISA at 11.25MHz
Anything above this frequency results in unstable system.
This is a bit surprising since the motherboard was happy at 48MHz base frequency with the BL3 CPU.
All BIOS settings on max except:
CACHE READ WAIT STATES = 1 W/S (best is 0)
BUS FREQUENCY SELECT = CLKIN/4 (best is /3)
This just worked. Nothing more to say really.
SpeedSys hangs which is common for many motherboards/SXL2 combos.
Intermediate performance.
--- AMD 386DX at 45MHz (1x45), ISA at 11.25MHz
All BIOS settings on max except:
CACHE READ WAIT STATES = 1 W/S (best is 0)
BUS FREQUENCY SELECT = CLKIN/4 (best is /3)

Performance is lacking - below medium compared to the bulk of previously tested motherboards.
Nothing more to say really.
---
benchmark results
I genuinely believed this motherboard would be incredible, but that turned out not to be the case. However, it is quite an intriguing assembly built around a lesser-known chipset, filled with peculiarities and limitations that provided me with an enjoyable challenge to explore.