'm thinking the only practical thing those pins can be used for at this point is /CE for more SPI stuff? 5 player adapter I think is superseded by Uzenet really, so a moot point, but perhaps people would do new stuff like Uze Thermometer or such. Or multiple bit-banged SPI devices with /CE...if this is "the" expansion to the finalized Uzebox form, might as well use it all. This is random thoughts from a professed non-hardware guy so...a few grains of salt may be necessary.
Rethinking about it, to make custom things using the SNES port, we would need a SNES cables that has 7 wires. All that I have from controllers have only 5. Also, It's probably better to use the EXT port since most uzebox out there already have it. I also see wifi being better than any multitap! So I think we should keep those two free pins for future use.
The 12 is a good idea to keep us in the loop of future firmware. The addon module as it currently is, could probably remain viable as well if we play our cards right or were you thinking of a new version using the 12+ also?
The simplest would be that I make a new version.
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I know I'm late to this thread, especially since you've designed a new PCB already, but have you looked into using the SPI RAM the way that the Logic Pirate uses it? I'm not sure if you saw the post I made about it in another thread.
Doing it that way, for streaming reads from SPI RAM (after setting up the address), you should be able to read an entire byte from SPI RAM -> internal SRAM in just a few clocks. The only hurdle with this approach is I'm not sure that you have an entire PORT free on the ATmega644 to read the entire byte from SPI RAM at once. Though, if you can spare 4 pins from the same PORT, you could probably beat 18 clocks per byte just by using a single RAM chip in QSPI mode, where each clock pulse allows you to read 4 bits out at once.
The other, even crazier option that might be possible, would be to use a tri-state buffer to somehow hook all 8 lines from two QSPI RAM chips directly into the R2R DAC, so you can dump an entire byte of raw color data directly to the video chip on every clock pulse.
We definitely don't have a free port for 8 bits, not even 4 right now with the SPI RAM CS, ESP reset and prog pins. Besides, adding all those chips defeats the idea of the Uzebox being simple and two chips. I was never hot even for the SPI ram since I never saw much gain that we can't already do with the SD interface. But it should comes handy with the ESP8266 (I hope!).