This runs entirely in your browser. Your firmware file is not uploaded anywhere, and the patcher refuses anything that isn't exactly Roland 5.52.
DOOM OS is included. The patched file contains DOOM OS 0.6.2-alpha (3824) and the MIDI Conductor together; patch Roland's stock file, not an existing DOOM OS one.
Experimental. Flashing modified firmware can brick your SP-404MKII, and this has only been tested on one unit
running Roland 5.52 with DOOM OS 0.6.2-alpha (build 3824). The patch hooks a few of Roland's own routines, which the DOOM OS author has called risky.
Keep the original Roland files so you can go back. Use at your own risk.
Release
0.2.0 alpha
For firmware
5.52
Includes
DOOM OS 0.6.2-alpha (3824), built in. Accepts only Roland 5.52.
Released
9 October 2026
1. Choose the file
Drop SP404MKII_APP1.bin from Roland's 5.52 update below. Keep the original SP404MKII_APP0.bin from the same download.
2. Install it
Download the patched SP404MKII_APP1.bin, keep that name, and install it with Roland's original SP404MKII_APP0.bin the way you install DOOM OS
(see the DOOM OS manual). To go back, install the original Roland files.
Then read the manual: SHIFT + FX1..FX6 turns MIDI mode on.