FRANK C64

Official page: frank.rh1.tech — hub for all FRANK boards and firmware.

Commodore 64 emulator for Raspberry Pi Pico 2 (RP2350) with HDMI/VGA output, SD card, and PS/2 keyboard.

Based on Frodo4 by Christian Bauer — a portable Commodore 64 emulator.

Supported Boards

This firmware is designed for the following RP2350-based boards with integrated HDMI, SD card, PS/2, and PSRAM:

• Murmulator — A compact retro-computing platform based on RP Pico 2, designed for emulators and classic games.
• FRANK — A versatile development board based on RP Pico 2, HDMI output, and extensive I/O options.

Both boards provide all necessary peripherals out of the box—no additional wiring required.

Features

• Full Commodore 64 PAL emulation (50 Hz)
• HDMI video output — Native 640x480 (320x240) via PIO
• VGA video output — Native 640x480 (320x240) via PIO (active accent color resistor DAC)
• 8MB QSPI PSRAM support for C64 RAM and disk images
• SD card support for D64/D81 disk images
• PS/2 and USB keyboard input
• NES/SNES gamepad support (directly and via USB)
• I2S audio output — High-quality SID emulation via external DAC
• PWM audio output — SID emulation without external DAC (directly via GPIO)
• Multiple CPU speed options: 378, 428 (VGA only), 504 MHz

Screenshots

Startup Screen

Emulator boot screen showing system information and initialization status.

Commodore 64 BASIC

Classic Commodore 64 BASIC interpreter ready for input.

Game: The Last Ninja

Demonstrating full game compatibility with smooth C64 emulation.

Game: Prince of Persia

Another classic title running at native C64 resolution and colors.

Hardware Requirements

• Raspberry Pi Pico 2 (RP2350) or compatible board
• 8MB QSPI PSRAM (mandatory!)
• Video output (choose one):
  • HDMI connector — directly connected via 270Ω resistors (no encoder needed)
  • VGA connector — accent color resistor DAC
• SD card module (SPI mode)
• PS/2 or USB keyboard
• Audio output (choose one):
  • I2S DAC module (e.g., TDA1387) — recommended for high-quality audio
  • PWM audio — no external DAC needed, directly via GPIO pins

PSRAM Options

FRANK C64 requires 8MB PSRAM to run. You can obtain PSRAM-equipped hardware in several ways:

1. Solder a PSRAM chip on top of the Flash chip on a Pico 2 clone (SOP-8 flash chips are only available on clones, not the original Pico 2)
2. Build a Nyx 2 — a DIY RP2350 board with integrated PSRAM
3. Purchase a Pimoroni Pico Plus 2 — a ready-made Pico 2 with 8MB PSRAM

Board Configurations

Two GPIO layouts are supported: M1 and M2. The PSRAM pin is auto-detected based on chip package:

• RP2350B: GPIO47 (both M1 and M2)
• RP2350A: GPIO19 (M1) or GPIO8 (M2)

HDMI (via 270Ω resistors)

Signal	M1 GPIO	M2 GPIO
CLK-	6	12
CLK+	7	13
D0-	8	14
D0+	9	15
D1-	10	16
D1+	11	17
D2-	12	18
D2+	13	19

VGA (accent color resistor DAC)

VGA uses the same base pins as HDMI. See Murmulator hardware documentation for resistor DAC wiring.

SD Card (SPI mode)

Signal	M1 GPIO	M2 GPIO
CLK	2	6
CMD	3	7
DAT0	4	4
DAT3/CS	5	5

PS/2 Keyboard

Signal	M1 GPIO	M2 GPIO
CLK	0	2
DATA	1	3

NES/SNES Gamepad

Signal	M1 GPIO	M2 GPIO
CLK	14	20
LATCH	15	21
DATA	16	22

I2S Audio

Signal	M1 GPIO	M2 GPIO
DATA	26	9
BCLK	27	10
LRCLK	28	11

PWM Audio

Signal	M1 GPIO	M2 GPIO
RIGHT	26	10
LEFT	27	11

Building

Prerequisites

1. Install the Raspberry Pi Pico SDK (version 2.0+)
2. Set environment variable: export PICO_SDK_PATH=/path/to/pico-sdk
3. Install ARM GCC toolchain

Build Steps

# Clone the repository with submodules
git clone --recursive https://github.com/rh1tech/frank-c64.git
cd frank-c64

# Or if already cloned, initialize submodules
git submodule update --init --recursive

# Build using the build script (development build with USB serial debug)
./build.sh

# Or build manually with CMake
mkdir build && cd build
cmake -DPICO_PLATFORM=rp2350 \
      -DBOARD_VARIANT=M1 \
      -DVIDEO_TYPE=VGA \
      -DAUDIO_TYPE=PWM \
      -DCPU_SPEED=378 ..
make -j$(nproc)

Release Builds

To build all firmware variants with version numbering and USB HID enabled:

./release.sh

This creates versioned firmware archives in the release/ directory:

• frank-c64_m1_X_XX.zip — All M1 board variants
• frank-c64_m2_X_XX.zip — All M2 board variants

Each archive contains firmware for all combinations:

• Video: VGA, HDMI
• Audio: I2S, PWM
• CPU Speed: 378, 428 (VGA only), 504 MHz

Filename format: frank-c64_mX_video_audio_speedmhz_version.uf2

Example: frank-c64_m1_vga_pwm_378mhz_1_02.uf2

Flashing

# With device in BOOTSEL mode:
picotool load build/frank-c64.uf2

# Or with device running:
picotool load -f build/frank-c64.uf2

# Or use the flash script:
./flash.sh

SD Card Setup

1. Format an SD card as FAT32
2. Create a c64 folder in the root
3. Copy your D64 or D81 disk images to the c64 folder

Keyboard Mapping

The keyboard layout uses VICE-style positional mapping:

PC:  ` 1 2 3 4 5 6 7 8 9 0 - =
C64: <- 1 2 3 4 5 6 7 8 9 0 + -

PC:  Q W E R T Y U I O P [ ]
C64: Q W E R T Y U I O P @ *

PC:  A S D F G H J K L ; '
C64: A S D F G H J K L : ;

PC:  Z X C V B N M , . /
C64: Z X C V B N M , . /

Special Keys

PC Key	C64 Key
Esc	RUN/STOP
Backspace	INS/DEL
Return	RETURN
Shift	SHIFT
Caps Lock	SHIFT LOCK
Tab	CTRL
L-Ctrl	CTRL
L-Alt	C= (Commodore)
\	^ (up arrow)
Home	CLR/HOME
End	£ (pound)

Function Keys and System Hotkeys

PC Key	Function
F1-F8	C64 F1-F8
F9	Swap joystick port
F10	Disk selector UI
F11	RESTORE (NMI)
Ctrl+Alt+Del	Reset C64

Joystick Emulation

Arrow keys can be used for joystick control (active on port 2 by default):

Key	Joystick Action
Arrow Up	Up
Arrow Down	Down
Arrow Left	Left
Arrow Right	Right
R-Ctrl	Fire
R-Alt	Fire

Press F9 to swap between joystick port 1 and port 2.

License

GNU General Public License v2 or later. See LICENSE for details.

This project is based on:

• Frodo4 by Christian Bauer — Portable Commodore 64 emulator

Authors

• Mikhail Matveev <xtreme@rh1.tech>
• DnCraptor — VGA driver, PWM audio, build system improvements

Acknowledgments

• Christian Bauer for the original Frodo C64 emulator
• The VICE team for VIC-II implementation reference
• xrip and DnCraptor for drivers and code contributions
• The Murmulator community for hardware designs and software support
• The Raspberry Pi foundation for the RP2350 and Pico SDK
• The Commodore 64 community for preserving this classic platform