MXM Mini GPU

[Paffo]

Hi,
sorry for creating an issue but i couldn't find your discord here on GH.
I was always interested in making the smallest GPU possible while still being able to more or less DIY it instead of buying it.

My current one is a GTX1060+Oculink and a small Server PSU, the full thing it's as big as a lunchbox, so not very 😅

When i found out that there are resellers for old or refurbished laptop GPUs, in MXM i thought i struck gold, however the MXM to PCIe adapters are prohibitively expensive in places like Aliexpress.

When i found your project i got the idea of slimming it down to be as small as possible, my current idea being Oculink (x4) as for the PCIe and a 200W12V GAN for the power, with just 3 DP ports as output.

Assembling such board would be a piece of cake as i work in electronic repairs, however designing it is another pair of hands, hence my question, do you think this is possible? How much complexity would be added if instead of oculink, straight on an ASM2464 for USB-C?

If the incredible (😂😂) Paint mockup didn't give you a stroke, what do you think?

[a-little-wifi]

Ohh interesting, I like the idea! OCuLink + external power would be far simpler to implement than with an ASM2464. While I have been experimenting with using that I haven't finished a design based on it and it'd be a lot more complex and expensive to produce. Maybe a separate USB4 to OCuLink board could be made later with that chip lol.
Anyway, what you're proposing is definitely possible I think. Is there any help you're looking for regarding it?

[Paffo]

i'd love to know anything you can tell me that could be counter intuitive, for example whether or not is possible to connect the PCIe lanes directly to the oculink connector or if i should pass it trough a signal amplifier IC. Technically it should not be needed as the cable runs will be short.
Plus, to "slim it down" is it a good idea to (for example) remove the VGA Connector, and from there backtrack to the MXM header deleting anything between the 2?

Im literally going into this blind let's say, i never made a PCB with such complexity, only small DIY projects, moreover i could not find any documentation on the MXM connector specifications or "standard" pinouts

[a-little-wifi]

Hmm so, one thing to note that I haven't addressed on the PCB in this repo yet, is that MXM cards don't have any of the DC-blocking capacitors on the PCIe lanes which are usually present for half of the pairs on a PCIe card, so they have to be included on the adapter PCB. Other than that I don't think a signal amplifier to redriver or whatever is necessary if the cable run is short enough yeah.
Assuming you don't have much experience routing high-speed differential signals (mostly PCIe and DP in this case), this series on hackaday is an excellent resource (check out the followup articles at the bottom too) https://hackaday.com/2023/03/14/pcie-for-hackers-the-diffpair-prelude/

To slim it down, for most things you don't intend to use you can just straight up remove them and everything related to them yeah, that'll be fine. There's a few parts that are important to the operation of the MXM card in general though, mostly the power and thermal control signals.

For documentation, it's really helped me to look at laptop schematics that include MXM slots for a known working reference implementation (the EliteBook 8540W one is particularly nice for having a directly connected DP port).
You can also find the MXM specification online if you search for something like 'MXM 3.1 specification pdf' (probably slightly less than legal for me to just upload it directly, so you'll have to find it yourself)

Let me know if there's anything else you need, I'm happy to help!