pico-zxspectrum

48k/128k ZX Spectrum for Raspberry Pico Pi RP2040

This is an attempt to make a basic 48k/128k ZX Spectrum emulation on the RP2040 with DVI output.

Uses Wren's Amazing PicoDVI and CarlK's Super no OS FAT FS for Pico libraries.

Features

• DVI over HDMI output
• USB Keyboard input
• PWM sound for ear, mic and AY-3-8912
• 12 quick save slots
• Load from .z80 snapshot files
• Read from .tap tape files

Screen shots

Wiring

	SPI0	GPIO	Pin	SPI	MicroSD 0	HDMI/DVI	Description
MISO	RX	4	6	DO	DO		Master In, Slave Out
CS0	CSn	5	7	SS or CS	CS		Slave (or Chip) Select
SCK	SCK	2	4	SCLK	CLK		SPI clock
MOSI	TX	3	5	DI	DI		Master Out, Slave In
CD		22	29		CD		Card Detect
GND			3		GND		Ground
3v3			36		3v3		3.3 volt power
GND			18,23			GND	Ground
GP16		16	21			TX2+	Data channel 2+
GP17		17	22			TX2-	Data channel 2-
GP18		18	24			TX1+	Data channel 1+
GP19		19	25			TX1-	Data channel 1-
GP12		12	16			TX0+	Data channel 0+
GP13		13	17			TX0-	Data channel 0-
GP14		14	19			TXC+	Clock +
GP15		15	20			TXC-	Clock -
GP20		20	26				PWM audio out

Components

Issues

USB host mode seems to work very reliably unless the keyboard is removed and reconnected, which causes the Pico to 'panic'.

This allows usb reconnect:
https://github.com/hathach/tinyusb/pull/1193/files

The Z80 is interrupted at the end of each frame at 60hz. The original Spectrum wrote frames at 50hz, so some code runs more frequently than it used to.

Some of the FAT SPI routines need to be kept in RAM, needs to be documented.

Build

This code needs to be cloned into the 'apps' folder of the PicoDVI library.

cd PicoDVI/software/apps
git clone git@github.com:fruit-bat/pico-zxspectrum.git zxspectrum
git clone git@github.com:fruit-bat/no-OS-FatFS-SD-SPI-RPi-Pico.git

In the 'apps' folder add the following line to CMakeLists.txt

add_subdirectory(zxspectrum)
add_subdirectory(no-OS-FatFS-SD-SPI-RPi-Pico/FatFs_SPI)

In the build folder:

cmake -DPICO_COPY_TO_RAM=0 ..
make -j4 ZxSpectrum
cp apps/zxspectrum/ZxSpectrum.uf2 /media/pi/RPI-RP2/

Prepare an SD card

The following folders need to be created on the SD card:

Folder	Contents
zxspectrum/snapshots	Put your .z80 snapshot files in here.
zxspectrum/quicksaves	Folder for quick saves.
zxspectrum/tapes	Folder for .tap tape files.

Special keys

Key	Action
AltGr	Symbol
F4	Toggle the Z80 moderator. Cycles through 3.5Mhz, 4.0Mhz and unmoderated
F5	play current tape
F6	play previous tape
F7	play next tape
F8	Reload current snap
F9	previous snap
F10	next snap
F11	Reset as 48k Spectrum
F12	Reset as 128k Spectrum
LCtrl + F1-F12	Quick save (LCtrl+F1 = save slot 1, LCtrl+F2 = save slot 2, etc)
LAlt + F1-F12	Quick load (LAlt+F1 = load slot 1, LAlt+F2 = load slot 2, etc)

Missing features

• HUD
• Audio input

References

Wren's Amazing PicoDVI
Z80 file format documentation
http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout
http://www.breakintoprogram.co.uk/computers/zx-spectrum/keyboard
http://www.breakintoprogram.co.uk/computers/zx-spectrum/interrupts
http://mdfs.net/Software/Spectrum/Harston/
https://www.1000bit.it/support/manuali/sinclair/zxspectrum/sm/section1.html
https://k1.spdns.de/Vintage/Sinclair/82/Sinclair%20ZX%20Spectrum/ROMs/gw03%20'gosh%2C%20wonderful'%20(Geoff%20Wearmouth)/gw03%20info.htm
https://worldofspectrum.org/faq/reference/48kreference.htm
https://worldofspectrum.org/faq/reference/128kreference.htm
http://www.zxdesign.info/cassette.shtml
https://uelectronics.info/2015/03/21/zx-spectrum-and-loaders-part-one/
https://mdfs.net/Software/Spectrum/ROMImages/
https://worldofspectrum.org/ZXSpectrum128Manual/sp128p13.html
https://cpctech.cpc-live.com/docs/ay38912/psgspec.htm
http://www.armory.com/~rstevew/Public/SoundSynth/Novelty/AY3-8910/start.html