3 * Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)
5 * This program is free software: you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, version 3 of the License.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program. If not, see <http://www.gnu.org/licenses/>.
26 #include "AlsaBridge.h"
29 static std::atomic<bool> run{true};
31 void interrupt(int signal) {
36 * The support for Pioneer DJ DJM-250MK2 (an external USB sound card / mixer) was added to the Linux (kernel) by these patches:
38 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=73d8c94084341e2895169a0462dbc18167f01683 (playback)
39 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=14335d8b9e1a2bf006f9d969a103f9731cabb210 (recording)
40 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=cdc01a1558dedcee3daee7e1802d0349a07edb87 (mixer setup)
42 * These patches are enough for playback and for recording from post CH faders.
44 * However this mixer is somehow incapacitated and if we want to record the raw signal from the PHONO or LINE channels,
45 * we only get silence. This feature is important for DVS (Digital Vinyl Systems) setups where
46 * the timecode signal from special control vinyls flows from mixer to the computer
47 * where it is interpreted in a software like MIXXX and used for controlling the playback of files on our computer.
48 * The signal (usually music) from these files flows back to the mixer and then to speakers and headphones.
50 * To make this work and enjoy all the features of the device we have bought, we need to tell the mixer that we
51 * want the signal instead of silence on given channels. And this is the purpose of the djm-fix utility and
52 * it is done by sending some magic packet to the mixer.
54 * Implementation of this magic in the AlsaBridge.cpp file is based on publicly available documentation
55 * that can be found at <https://mixb.me/CDJHidProtocol/hid-analysis/handshake.html>.
56 * This page pointed me to the proper hash function (according to the constants, it is bit uncommon but publicly known Fowler–Noll–Vo hash function, FNV)
57 * and some magic bits. I wrote this standalone C++ program that talks with the mixer over MIDI SysEx messages and does the magic.
59 * When this program is started, it finds the mixer and makes it fully working.
60 * It needs to be running all the time, otherwise we will get silence on the PHONO/LINE channels again.
62 * Install dependencies:
63 * apt install mercurial make pkg-config g++ libasound2-dev # in Debian or Ubuntu (it will be similar in other distributions)
66 * hg clone https://hg.frantovo.cz/midi/djm-fix/ # primary source
67 * hg clone https://hg.globalcode.info/midi/djm-fix/ # or we can use this mirror
70 * make # we can skip this step, it will be compiled on the first run
73 * make run # in most cases
74 * build/djm-fix 'Pioneer DJ.*' # or provide custom name pattern (regular expression) to select the proper card
79 * Look for updates in the Mercurial repositories and at <https://blog.frantovo.cz/c/387/>.
82 int main(int argc, char**argv) {
83 using L = djmfix::logging::Level;
84 std::unique_ptr<djmfix::logging::Logger> logger(djmfix::logging::create(std::cerr, L::INFO));
86 logger->log(L::INFO, "djm-fix started");
87 std::string cardNamePattern = argc == 2 ? argv[1] : "Pioneer DJ.*";
89 signal(SIGINT, interrupt);
90 std::unique_ptr<djmfix::DJMFix> djmFix(djmfix::create(logger.get()));
91 std::unique_ptr<djmfix::alsa::AlsaBridge> alsaBridge(djmfix::alsa::create(djmFix.get(), cardNamePattern, logger.get()));
94 while (run) std::this_thread::sleep_for(std::chrono::milliseconds(100));
96 std::cerr << std::endl;
97 logger->log(L::INFO, "djm-fix stopping");
102 } catch (const std::exception& e) {
103 logger->log(L::SEVERE, e.what());