Been working on the stereo system CPU card again. I tried *really hard* to get the stupid USB interface done aaaand not only did I not do that I discovered something that made things even more complicated to figure out.

Currently there's an 8 pin connector that has two CAN buses plus power and ground. But I'm probably gonna have to drop one if I want the USB port to have dual-role functionality since it shares pins with the I²C bus I'd need for the USB controller chip.

Alternatively I could maybe use a microcontroller as a protocol converter but then the backpack expansion header would have to go away. That'd free up some space but I'm not sure it'd all still fit since it's not an integrated solution.

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But another big choice is I've realized I could probably power the system via the USB port, too, using the 20V/5A standard. PCIe connectors are (kinda) rated to 75W which would be enough. For that I'd have to use *both* the CAN/I²C *and* the expansion header GPIO lines.

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So, like, I dunno.
1x CAN bus
1x DRP USB-C with Power Delivery + Accessory support
vs.
1x CAN bus
1x DRP USB-C only
1x GPIO/SPI Expansion Header w/Clock source
vs.
2x CAN bus
1x UFP USB-C
1x GPIO/SPI etc

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Did a bunch of other posts on Twitter I forgot to crosspost, but that's okay because: NEW PLAN! (Re)discovered the UPD350B aaaaaand yep, it uses SPI, does PD 3.0 comms, has GPIO, it's pretty much fantastic as far as USB-C port controllers go. (Which, you know, could be better, could be worse.)

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Basically I'll have parallel SPI connections for the GPIO header + controller, maybe put some of the GPIO of the port controller onto the header, too. Will see, have to fuck around. PD 75W+ may be done through the header too. All stuff to figure out as I work on it.

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When you're trying to label pins in a compact manner but are basically reduced to doing pixel art.
*looks at the analog inputs symbol, only sees a dreidel*

Thinking about putting a hash of the source file on the board. Absolutely no way to verify that's actually what was used, but in non-bad-actor cases it'd let you be sure which version you sent out.

A shame there's no standard for the fab-house auto-inserting it so the hash would actually verify without having to make a different copy of the file with the hash on it just for manufacturing.

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On the plus side, I'm hoping to get this sent off to the fab by the end of the month. We'll see if it happens or not, but I've gotten past most of the roadblocks in making this so, fingers crossed!

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