Pico Micro Mac (pico-umac)

v0.21-fruitjam 28 March 2025

I (@jepler) have run roughshod across the code, breaking things willy-nilly and adding

512x342 & 640x480 digital output on HSTX
PIO USB
PSRAM support
Some Sound support on the onboard I2S DAC (speaker and headphones)

Several pre-compiled variants are offered:

400kB or 4096kB (the latter uses PSRAM, and may perform slower overall but can run more software)
512x342 or 640x480 desktop resolution (512x342 is more compatible but has black screen margins)
overclocked or not (overclocked may run faster but may be less reliable)

What works?

System beep
Dark Castle including audio
After Dark screensavers including audio
Glider works, but without sound

What doesn't work?

Hypercard "play" and some hypercard screen transitions

Some of the software I tested with:

Plug mouse & keyboard into the USB ports of the fruit jam.

Put the software (a mac HFS volume with no additional headers or metadata) on a SD card as "umac0w.img" (if you want to be able to write files) or "umac0ro.img" (if you want the drive to be read only) and press the reset button to start.

Important note on overclocking: The "oc" uf2 files overclock your RP2 chip to 264MHz. Simply including the <Adafruit_dvhstx.h> header enables this overclocking, separate from the option in the Arduino Tools menu. Just like PC overclocking, there’s some risk of reduced component lifespan, though the extent (if any) can’t be precisely quantified and could vary from one chip to another. Proceed at your own discretion.

v0.21 20 December 2024

This project embeds the umac Mac 128K emulator project into a Raspberry Pi Pico microcontroller. At long last, the worst Macintosh in a cheap, portable form factor!

It has features, many features, the best features:

Outputs VGA 640x480@60Hz, monochrome, using three resistors
USB HID keyboard and mouse
Read-only disc image in flash (your creations are ephemeral, like life itself)
Or, if you have a hard time letting go, support for rewritable disc storage on an SPI-attached SD card
Mac 128K by default, or you can make use of more of the Pico's memory and run as a Mac 208K
Since you now have more memory, you can splash out on more screen real-estate, and use 640x480 resolution!

Great features. It even doesn't hang at random! (Anymore.)

The Mac 208K was, of course, never a real machine. But, umac supports odd-sized memories, and more memory runs more things. A surprising amount of software runs on the 128K config, but if you need to run MacPaint specifically then you'll need to build both SD storage in addition to the Mac 208K config.

So anyway, you can build this project yourself for less than the cost of a beer! You'll need at least a RPi Pico board, a VGA monitor (or VGA-HDMI adapter), a USB mouse (and maybe a USB keyboard/hub), plus a couple of cheap components.

Build

Prerequisites/essentials

git submodules
- Clone the repo with --recursive, or git submodule update --init --recursive
Install/set up the Pico/RP2040 SDK
Get a ROM & disc image with sh fetch-rom-dsk.sh (needs curl & 7z (debian package p7zip-full))

Build pico-umac

Run the configure-and-build script:

$ ./fruitjam-build.sh -h
Usage: ./fruitjam-build.sh [-v] [-m KiB] [-d diskimage]

   -v: Use framebuffer resolution 640x480 instead of 512x342
   -m: Set memory size in KiB (over 400kB requires psram)
   -d: Specify disc image to include
   -o: Overclock to 264MHz (known to be incompatible with psram)

PSRAM is automatically set depending on memory & framebuffer details

Disc image

If you don't build SD support, an internal read-only disc image is stored in flash. If you do build SD support, you have the option to still include an image in flash, and this is used as a fallback if SD boot fails.

Grab a Macintosh system disc from somewhere. A 400K or 800K floppy image works just fine, up to System 3.2 (the last version to support Mac128Ks). I've used images from https://winworldpc.com/product/mac-os-0-6/system-3x but also check the various forums and MacintoshRepository. See the umac README for info on formats (it needs to be raw data without header).

The image size can be whatever you have space for in flash (typically about 1.3MB is free there), or on the SD card. (I don't know what the HFS limits are. But if you make a 50MB disc you're unlikely to fill it with software that actually works on the Mac 128K :) )

If using an SD card, use a FAT-formatted card and copy your disc image into one of the following files in the root of the card:

umac0.img: A normal read/write disc image
umac0ro.img: A read-only disc image

Software

Both CPU cores are used, and are optionally overclocked (blush) to 264MHz so that Missile Command is enjoyable to play.

The umac emulator and video output runs on core 1, and core 0 deals with USB HID input. Video DMA is initialised pointing to the framebuffer in the Mac's RAM, or to a mirrored region in SRAM depending on the configuration.

Other than that, it's just a main loop in main.c shuffling things into umac.

Quite a lot of optimisation has been done in umac and Musashi to get performance up on Cortex-M0+ and the RP2040, like careful location of certain routines in RAM, ensuring inlining/constants can be foldeed, etc. It's 5x faster than it was at the beginning.

The top-level project might be a useful framework for other emulators, or other projects that need USB HID input and a framebuffer (e.g. a VT220 emulator!).

The USB HID code is largely stolen from the TinyUSB example, but shows how in practice you might capture keypresses/deal with mouse events.

Licence

hid.c and tusb_config.h are based on code from the TinyUSB project, which is Copyright (c) 2019, 2021 Ha Thach (tinyusb.org) and released under the MIT licence. sd_hw_config.c is based on code from the no-OS-FatFS-SD-SPI-RPi-Pico project, which is Copyright (c) 2021 Carl John Kugler III.

The remainder of the code is released under the MIT licence:

Copyright (c) 2024 Matt Evans:

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

adafruit/pico-mac

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