4 hours ago, paulscottrobson said:
So there's a compromise, which is essentially video on one chip, and everything else with real parts. The main problem with this seems to be timing, which seems to have caused various other CPLD and MCUs to be added (not sure exactly what), and some things moved to Vera. So sound is now on Vera, and it's a moot point whether there's an advantage in having a real sound chip as well. The PS/2 keyboard interface was supposed to be done over the PIA as well, never quite sure how/if that worked given it's a slow clock. It wouldn't surprise me if that moves onto Vera as well. ...
Pinning down some details that are a bit loose here.
There aren't "various other CPLD and MCU's" added due to problems with "timing". The problems with timing were handled by getting the chip select sequence with R/W and clock phase right for the chips which variously expect 6502 style bus timing (leading select), Z80 style bus timings (synchronous select) and PICBUS style timings (leading R/W), but that was a matter of getting the correct versions of chip select signals from the glue logic chip select circuitry, as some needed to be OR'd synchronous with the clock and some needed to be asynchronous.
The problem with timing with the AY3 sound chip led to replacement with a different PSG sound chip, the SAA1099. IIRC, it was mentioned on Facebook that Frank's plan for Vera from the outset was to include PSG capabilities, so PSG on Vera is more about the design goals of the Vera designer making the SAA1099 PSG redundant than about issues integrating the SAA1099 sound chip. The YM2151 is an FM chip, which completes the 1980's "chiptunes trinity" of PSG, FM and PCM.
The MCU is an 8bit MCU ATTiny to handle the power management on the ATX power supply, which is not a pure old fashioned "dumb" power supply but includes a signal from the PS whether some characteristic of the current is valid. The version 1 and 2 prototypes had a circuit done with glue logic which apparently was working with the PS they had but when tried with some other ATX power supplies could be a bit flaky. After all, ATX power supplies assume that the motherboard has a microcontroller handling power on/off etc. It is accessed via I2C bit banged on a 6522 VIA.
The PS2 can't move to Vera, there aren't enough pins. The two options are handling the PS2 with a VIA or handling it with a version of the ATTiny with more pins (which would, of course, be quite period "consistent", as the original AT keyboard/mouse interface that the PS2 was evolved from was handled with an 8bit MCU). If they end up using the ATTiny, then an MCU may end up being used to deal with a timing issue, but it was added to integrate with ATX power supplies under the ATX specification, rather than "it works with what we have on hand".