Unimplemented:
            
  A nice GUI
  Gamma
  CLK_70
  DIP switches
  Audio:
   CODEC
   PSGs (partial)
   SIDs
   OPL3
  Timing:
   VIA timers/serial/handshake
  PS/2 mouse
  Mouse pointer PS/2 input (Pointer display works)
  C64 keyboard
  UART (RS232 or WiFi)
  DMA interrupts
  Buzzer (maybe implement with audio? could just ignore it)
  F256jr status LEDs
  Software reset
  Hardware version info
  CPU selection (6809, 65816)
  Upload new flash
  Boot from RAM
  RAM expansion
  Flash expansion
  SDCard insertion interrupt

Acceptable lameness: (for now)
  
  CPU: Not cycle accurate. Each instruction takes 1 cycle per byte read/written. Closer, but real CPU takes more.
  DMA: occurs instantly, BUSY is always 0
  PS/2 keyboard: Output to it is always ACKed and ignored
  NES/SNES: scan happens instantly
  SPI: Only direct support for SD card commands that the microkernel uses
  PRNG: Always gives random numbers, all else ignored. Won't match real thing without cycle exactness anyway.
  IEC: not implemented in emulator
  RTC: Watchdog timer ignored