diff options
Diffstat (limited to 'sound/usb/midi.c')
| -rw-r--r-- | sound/usb/midi.c | 80 |
1 files changed, 74 insertions, 6 deletions
diff --git a/sound/usb/midi.c b/sound/usb/midi.c index 779d97d31f17..826ac870f246 100644 --- a/sound/usb/midi.c +++ b/sound/usb/midi.c @@ -489,16 +489,84 @@ static void ch345_broken_sysex_input(struct snd_usb_midi_in_endpoint *ep, /* * CME protocol: like the standard protocol, but SysEx commands are sent as a - * single USB packet preceded by a 0x0F byte. + * single USB packet preceded by a 0x0F byte, as are system realtime + * messages and MIDI Active Sensing. + * Also, multiple messages can be sent in the same packet. */ static void snd_usbmidi_cme_input(struct snd_usb_midi_in_endpoint *ep, uint8_t *buffer, int buffer_length) { - if (buffer_length < 2 || (buffer[0] & 0x0f) != 0x0f) - snd_usbmidi_standard_input(ep, buffer, buffer_length); - else - snd_usbmidi_input_data(ep, buffer[0] >> 4, - &buffer[1], buffer_length - 1); + int remaining = buffer_length; + + /* + * CME send sysex, song position pointer, system realtime + * and active sensing using CIN 0x0f, which in the standard + * is only intended for single byte unparsed data. + * So we need to interpret these here before sending them on. + * By default, we assume single byte data, which is true + * for system realtime (midi clock, start, stop and continue) + * and active sensing, and handle the other (known) cases + * separately. + * In contrast to the standard, CME does not split sysex + * into multiple 4-byte packets, but lumps everything together + * into one. In addition, CME can string multiple messages + * together in the same packet; pressing the Record button + * on an UF6 sends a sysex message directly followed + * by a song position pointer in the same packet. + * For it to have any reasonable meaning, a sysex message + * needs to be at least 3 bytes in length (0xf0, id, 0xf7), + * corresponding to a packet size of 4 bytes, and the ones sent + * by CME devices are 6 or 7 bytes, making the packet fragments + * 7 or 8 bytes long (six or seven bytes plus preceding CN+CIN byte). + * For the other types, the packet size is always 4 bytes, + * as per the standard, with the data size being 3 for SPP + * and 1 for the others. + * Thus all packet fragments are at least 4 bytes long, so we can + * skip anything that is shorter; this also conveniantly skips + * packets with size 0, which CME devices continuously send when + * they have nothing better to do. + * Another quirk is that sometimes multiple messages are sent + * in the same packet. This has been observed for midi clock + * and active sensing i.e. 0x0f 0xf8 0x00 0x00 0x0f 0xfe 0x00 0x00, + * but also multiple note ons/offs, and control change together + * with MIDI clock. Similarly, some sysex messages are followed by + * the song position pointer in the same packet, and occasionally + * additionally by a midi clock or active sensing. + * We handle this by looping over all data and parsing it along the way. + */ + while (remaining >= 4) { + int source_length = 4; /* default */ + + if ((buffer[0] & 0x0f) == 0x0f) { + int data_length = 1; /* default */ + + if (buffer[1] == 0xf0) { + /* Sysex: Find EOX and send on whole message. */ + /* To kick off the search, skip the first + * two bytes (CN+CIN and SYSEX (0xf0). + */ + uint8_t *tmp_buf = buffer + 2; + int tmp_length = remaining - 2; + + while (tmp_length > 1 && *tmp_buf != 0xf7) { + tmp_buf++; + tmp_length--; + } + data_length = tmp_buf - buffer; + source_length = data_length + 1; + } else if (buffer[1] == 0xf2) { + /* Three byte song position pointer */ + data_length = 3; + } + snd_usbmidi_input_data(ep, buffer[0] >> 4, + &buffer[1], data_length); + } else { + /* normal channel events */ + snd_usbmidi_standard_input(ep, buffer, source_length); + } + buffer += source_length; + remaining -= source_length; + } } /* |