TIPI update, or "How I spent most of my 4th of July weekend":
I have spent the better part of June futzing around with a flaky broadboard trying to verify that the reduced wiring model to the Raspberry PI will work. I'm convinced it does.
So I've started on pcboard layout. First go at a layout and routing looks like this:
I'm fairly certain, that I'll have to basically do it all over again I think the CPLD footprint is going to be too small. Not 100% sure the size of the part. So I've ordered parts, and will do a fitting on paper.
I also need to read the spec on the JTAG interface. I've seen it done without pull-up resisters, and I've read that they are advised. I've also read that they are built into the CPLD... so I'll need to clarify that.
Corey wanted extra LEDs for debugging... but there are only 4 I/Os on the CPLD unused. I have brought them out to solder pads instead.
I've wired the TI external interrupt to the CPLD, just in case we want to do interrupt work in the future. But so far all of the things I've demonstrated do not require TI interrupt handling.
I'm aiming at a 32k eprom with CRU based bank switching.
Other things wrong with this pcboard layout:
Overall size doens't match my 32k board.
via's are too small for my comfort
header drill sizes are too small for my comfort - with the 32k board, I started having trouble getting the headers in on some prints... inconsistency in the plating I suppose.
I expect to find I do need 4 pull-ups on the JTAG port.
I need to migrate the verilog to a new project targetting this chip instead of my FPGA. And verify that my pin assignments are satisfactory.
Something that is nice about working with the CPLD, is that I can just untangle traces by re-assigning pins... This is true of the Raspberry PI connection as well. If this wasn't the case, I'd have gone nuts...
Once I get parts, to test fitting, I'll have to scrap this, and start over. but with a good idea of how to route. And then once Corey and I have hardware, there is a ton of software work to do still.
I have a side project that I'm working on with SMD parts, so I can practice.