Feature Request: Horizontal / 3rd PDS Slot for passthrough for accelerator (ala Bolle Ethernet)

[erikbuild]

It would be amazing to have a horizontal takeoff PDS slot similar to the one on Bolle's Ethernet card. This would allow usage of an accelerator in the horizontal position and allow for the top card stack to be one of the Grayscale cards out there.

I know this is an extremely popular combination on the SE/30 community (namely, Bolle Ethernet combo + Grayscale + Carrera040 or similar).

I have a Zigzagjoe Grayscale Card that I would love to combine with this and be able to optionally stack in an accelerator in the future.

I'm not sure if this is feasible, but I would be happy to try banging my head against it a bit if anybody has an idea of what would be required electrically.

[rhalkyard]

Thanks for the feedback! I did give some thought to doing things that way, but there a few reasons I didn't - for one, I don't have any such accelerators to test fit and compatibility with, and can't really justify the expense of acquiring them. Additionally, having built a few ethernet cards up, I've become less convinced that the 'tall' form factor is the way to go. It makes for an unnecessarily large board, which increases the production cost, and the long signal runs seem to introduce signal-integrity issues that I'm not really smart enough to resolve.

If I understand correctly, the side-mounted slot on Bolle's card isn't a direct connection to the PDS slot. I think it's meant to take IIci cache cards, with logic on the board to interface it to the rest of the bus, but that's Bolle's secret recipe and I'm not sure what it actually involves. No reason why you couldn't just put a second PDS slot there instead of a cache slot, I suppose, but signal integrity might become even more of a problem - in particular the 16MHz clock gets pretty nasty, and the rise-times on the open-collector /DSACK lines can be problematically slow, especially with a accelerator thrown into the mix (I run a Zigzagjoe processor-socket accelerator, and slow-rising /DSACK plays havoc with it).

I do have a revised design in the works, where I've ditched the tall form-factor in favour of the lower profile used by most original ethernet cards and the Zigzagjoe grayscale card. This should make the card compatible with the IIsi, and also be more amenable to stacking up multiple cards with pass-through slots. The revised design also incorporates buffering to try to deal with the signal-integrity issues, and has a fix for a couple of minor hardware bugs (#4 being the most annoying of them).

I'll admit that this project has fallen by the wayside a bit - between other projects, life events, and the uncertain situation with China-US shipping and tariffs, I haven't yet pulled the trigger on a new batch of boards. If you're still keen on the idea of a horizontal-slot version, I'd be happy to help out with the design process - this would be good motivation for me to clean up my work-in-progress and get it uploaded!