/**
* DJM-Fix
* Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <memory>
#include <iostream>
#include <chrono>
#include <thread>
#include <csignal>
#include <atomic>
#include "DJMFix.h"
#include "AlsaBridge.h"
static std::atomic<bool> run{true};
void interrupt(int signal) {
run = false;
std::cerr << "interrupt()" << std::endl; // TODO: do not mess STDIO
}
/**
* The support for Pioneer DJ DJM-250MK2 (an external USB sound card / mixer) was added to the Linux (kernel) by these patches:
*
* - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=73d8c94084341e2895169a0462dbc18167f01683 (playback)
* - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=14335d8b9e1a2bf006f9d969a103f9731cabb210 (recording)
* - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=cdc01a1558dedcee3daee7e1802d0349a07edb87 (mixer setup)
*
* These patches are enough for playback and for recording from post CH faders.
*
* However this mixer is somehow incapacitated and if we want to record the raw signal from the PHONO or LINE channels,
* we only get silence. This feature is important for DVS (Digital Vinyl Systems) setups where
* the timecode signal from special control vinyls flows from mixer to the computer
* where it is interpreted in a software like MIXXX and used for controlling the playback of files on our computer.
* The signal (usually music) from these files flows back to the mixer and then to speakers and headphones.
*
* To make this work and enjoy all the features of the device we have bought, we need to tell the mixer that we
* want the signal instead of silence on given channels. And this is the purpose of the djm-fix utility and
* it is done by sending some magic packet to the mixer.
*
* Implementation of this magic in the AlsaBridge.cpp file is based on publicly available documentation
* that can be found at <https://mixb.me/CDJHidProtocol/hid-analysis/handshake.html>.
* 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)
* and some magic bits. I wrote this standalone C++ program that talks with the mixer over MIDI SysEx messages and does the magic.
*
* When this program is started, it finds the mixer and makes it fully working.
* It needs to be running all the time, otherwise we will get silence on the PHONO/LINE channels again.
*
* Install dependencies:
* apt install mercurial make pkg-config g++ libasound2-dev # in Debian or Ubuntu (it will be similar in other distributions)
*
* Download djm-fix:
* hg clone https://hg.frantovo.cz/midi/djm-fix/ # primary source
* hg clone https://hg.globalcode.info/midi/djm-fix/ # or we can use this mirror
*
* Compile:
* make # we can skip this step, it will be compiled on the first run
*
* Run:
* make run
*
* Stop:
* press Ctrl+C
*/
int main(int argc, char**argv) {
std::string deviceName = argc == 2 ? argv[1] : "hw:1"; // FIXME: parse CLI options + automatic device search
signal(SIGINT, interrupt);
std::unique_ptr<djmfix::DJMFix> djmFix(djmfix::create());
std::unique_ptr<djmfix::alsa::AlsaBridge> alsaBridge(djmfix::alsa::create(djmFix.get(), deviceName));
alsaBridge->start();
while (run) std::this_thread::sleep_for(std::chrono::milliseconds(100));
alsaBridge->stop();
return 0;
}