30 void interrupt(int signal) { |
30 void interrupt(int signal) { |
31 run = false; |
31 run = false; |
32 std::cerr << "interrupt()" << std::endl; // TODO: do not mess STDIO |
32 std::cerr << "interrupt()" << std::endl; // TODO: do not mess STDIO |
33 } |
33 } |
34 |
34 |
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35 /** |
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36 * The support for Pioneer DJ DJM-250MK2 (an external USB sound card / mixer) was added to the Linux (kernel) by these patches: |
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37 * |
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38 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=73d8c94084341e2895169a0462dbc18167f01683 (playback) |
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39 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=14335d8b9e1a2bf006f9d969a103f9731cabb210 (recording) |
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40 * - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/usb?id=cdc01a1558dedcee3daee7e1802d0349a07edb87 (mixer setup) |
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41 * |
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42 * These patches are enough for playback and for recording from post CH faders. |
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43 * |
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44 * However this mixer is somehow incapacitated and if we want to record the raw signal from the PHONO or LINE channels, |
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45 * we only get silence. This feature is important for DVS (Digital Vinyl Systems) setups where |
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46 * the timecode signal from special control vinyls flows from mixer to the computer |
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47 * where it is interpreted in a software like MIXXX and used for controlling the playback of files on our computer. |
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48 * The signal (usually music) from these files flows back to the mixer and then to speakers and headphones. |
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49 * |
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50 * To make this work and enjoy all the features of the device we have bought, we need to tell the mixer that we |
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51 * want the signal instead of silence on given channels. And this is the purpose of the djm-fix utility and |
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52 * it is done by sending some magic packet to the mixer. |
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53 * |
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54 * Implementation of this magic in the AlsaBridge.cpp file is based on publicly available documentation |
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55 * that can be found at <https://mixb.me/CDJHidProtocol/hid-analysis/handshake.html>. |
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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) |
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57 * and some magic bits. I wrote this standalone C++ program that talks with the mixer over MIDI SysEx messages and does the magic. |
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58 * |
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59 * When this program is started, it finds the mixer and makes it fully working. |
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60 * It needs to be running all the time, otherwise we will get silence on the PHONO/LINE channels again. |
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61 * |
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62 * Install dependencies: |
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63 * apt install mercurial make pkg-config g++ libasound2-dev # in Debian or Ubuntu (it will be similar in other distributions) |
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64 * |
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65 * Download djm-fix: |
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66 * hg clone https://hg.frantovo.cz/midi/djm-fix/ # primary source |
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67 * hg clone https://hg.globalcode.info/midi/djm-fix/ # or we can use this mirror |
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68 * |
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69 * Compile: |
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70 * make # we can skip this step, it will be compiled on the first run |
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71 * |
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72 * Run: |
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73 * make run |
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74 * |
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75 * Stop: |
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76 * press Ctrl+C |
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77 */ |
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78 |
35 int main(int argc, char**argv) { |
79 int main(int argc, char**argv) { |
36 std::string deviceName = argc == 2 ? argv[1] : "hw:1"; // FIXME: parse CLI options + automatic device search |
80 std::string deviceName = argc == 2 ? argv[1] : "hw:1"; // FIXME: parse CLI options + automatic device search |
37 |
81 |
38 signal(SIGINT, interrupt); |
82 signal(SIGINT, interrupt); |
39 std::unique_ptr<djmfix::DJMFix> djmFix(djmfix::create()); |
83 std::unique_ptr<djmfix::DJMFix> djmFix(djmfix::create()); |
40 std::unique_ptr<djmfix::alsa::AlsaBridge> alsaBridge(djmfix::alsa::create(djmFix.get(), deviceName)); |
84 std::unique_ptr<djmfix::alsa::AlsaBridge> alsaBridge(djmfix::alsa::create(djmFix.get(), deviceName)); |
41 |
85 |
42 alsaBridge->start(); |
86 alsaBridge->start(); |