7.4 KiB


This project is a bootloader and firmware for a Macintosh ROM SIMM programmer, along with control software for Mac OS X, Windows, and Linux. The ROM SIMM is compatible with the SE/30, IIx, IIcx, IIci, IIfx, and IIsi.

This particular repository contains the main firmware that runs on the programmer board. There are two variants of the firmware that are built from this source code:

  1. The firmware for my original programmer, the Big Mess o' Wires programmer, and the CayMac Vintage revision 1 programmer. These programmers use the Atmel/Microchip AT90USB646/1286 AVR microcontroller. The current compiler version used with this version of the firmware is avr-gcc 4.8.2. Using a different version of gcc may result in worse performance due to some very tight optimizations performed on this project to decrease programming time.
  2. The firmware for the CayMac Vintage ROMmate-2, which uses the Nuvoton M258KE3AE ARM Cortex-M23 microcontroller. The compiler that has been tested with this firmware is ARM GCC 6-2017-q1-update.


Binary downloads can be found at the following links:


The project is spread over a few repositories. Some of them have a wiki.

Repository Repository location Wiki location
Programmer Firmware (AVR microcontroller)
Bootloader (AVR microcontroller)
Programmer Software (Windows/Mac/Linux) none
Windows Driver (.inf file, not needed on Windows 10) none
CAD for programmer, along with 2 MB and 8 MB SIMM PCBs none
Mac ROM patcher (from none

Firmware compilation instructions


This firmware is used on my original programmer, the BMOW programmer, and CayMac's original programmer.

As mentioned earlier, this is an AVR project that is currently optimized for avr-gcc 4.8.2. It can be built using either CMake or Eclipse with the AVR Eclipse plugin. To build with CMake, make sure avr-gcc is in your path, and then run:

mkdir build_avr
cd build_avr
cmake -DCMAKE_TOOLCHAIN_FILE=../toolchain-avr.cmake ..


This firmware is used on the CayMac ROMmate-2.

Tested with ARM GCC 6-2017-q1-update. To build with CMake, make sure arm-none-eabi-gcc is in your path, and then run:

mkdir build_arm
cd build_arm
cmake -DCMAKE_TOOLCHAIN_FILE=../toolchain-m258ke.cmake ..

Common information

The build processes described above will create a SIMMProgrammer.bin file that can be programmed to the board using the Windows/Mac/Linux software. You can also generate a combined firmware image containing both the AVR and ARM builds that automatically flashes the correct firmware based on the detected board when using software version 2.0 or newer:

cat build_avr/SIMMProgrammer.bin \
    <(echo -en "\xDB\x00\xDB\x01\xDB\x02\xDB\x03\xDB\x04\xDB\x05\xDB\x06\xDB\x07") \
    <(echo -en "\xDB\x08\xDB\x09\xDB\x0A\xDB\x0B\xDB\x0C\xDB\x0D\xDB\x0E\xDB\x0F") \
    <(echo -en "\xDB\xDB\xDB\xDB\xAA\xAA\xAA\xAA\xDB\xDB\xDB\xDB\x55\x55\x55\x55") \
    build_arm/SIMMProgrammer.bin \
    > SIMMProgrammerFirmware.bin



What Where
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