This is a release of the "pico" fork of unrealspeccyp, because people keep asking for it!

See this project's README.md for more information.

Features

Spectrum 48K and 128K emulator based on unrealspeccyp.
VGA output.
Beeper output pin for 48K spectrum (i.e. just wiggling the pin like the real Spectrum!).
AY sound output for 128K spectrum.
.TAP, .SNA, .Z80 support (embedded in binary).
This port was development during pre-silicon RP2040 development. Therefore, it had to run at 48Mhz, and indeed.
both 48K and 128K emulators still run by default at a 48Mhz system clock.
Read/Write on RP2040 GPIO pins - because why not? (see bitbang app).

Some caveats

The sole reason for this project's existence was as a system test/bit of fun during early development of the RP2040, it is
not intended to be the best, full-featured emulator. I have open sourced it as people keep asking!
'Khan' is the codename I used to keep what I was doing secret :-)
No doubt these terse instructions will prove frustrating for some; feel free to submit PRs!
You cannot currently use beeper/tape noise and AY sound at the same time (as they use different mechanisms) -
actually I think there is support for using one PWM channel for each, but IDK if it still works.
I did some recent cleanup in preparation for open-source:
- Untangled the horrible mess of symlinks that had this building within another makefile project prior to the Pico
  SDK.
- Added USB keyboard support (this seems fine - though I had to hunt for more RAM, so it is possible this may
  break something - you can run with or without).
- Hopefully got a license on everything important.
- Added some I2S support - this is only for AY sound as the beeper just wiggles a pin. Sadly my I2S decoder
  doesn't like 22050Hz, so I had to up it to 24000Hz. I don't necessarily recommend using this if you can use PWM
  (the default).