So up to two SRAMs can be installed on this tiny 2″ x 2″ board. To the right is the connector, and the SRAMs are on the left. With current SRAM sizes, you can install 32-megabit SRAMs. That’s 4 Megabyte each. This will be in addition to the 8MB onboard SDRAM.
Our current memory controller, while integrated and functioning fine, is just too slow. I already have the SRAMs and the connectors, from my previous attempt hardwire attempt. See bottom photo at previous link. But there were hardware “bugs”, maybe solder bridges or wiring mistakes, that I simply didn’t feel like messing around with. This PCB is a heck of a lot cleaner solution, and the chance for problems will be lower. The signal quality will be much better.
I’m in the process of writing a Finite State Machine to perform an independent test of the memory. And then I’ve got to find a place in the memory map for it, and then write some glue logic to integrate it. This should be easier now that I’ve done the FLASH(the UFM) and the SDRAM.
The SDRAM controller has really high latency (on the order of 8+ cycles) and while there were probably workarounds, the single-cycle 10ns latency of these SRAMs is just so attractive, that I think I’m shooting myself in the foot by not chasing the solution down earlier.
I submitted this PCB to Elecrow PCB in China. I had originally tried using 3pcb/pcbway, but their lack of communication and bait-and-switch pricing quote practically ensured my lack of business. Elecrow, on the other hand, has been great with communication. Their pricing is great. I ordered red-colored PCBs for no extra charge and I’m really looking forward to getting them. I paid extra for their rush service, and for fedex. I could have them as early as the end of the week, but we’ll see!
Again, I have to thank my friend Brian for his kicad skills. It would have taken me much longer, with questionable results.