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Diffstat (limited to 'Documentation/sound/designs/midi-2.0.rst')
| -rw-r--r-- | Documentation/sound/designs/midi-2.0.rst | 39 |
1 files changed, 33 insertions, 6 deletions
diff --git a/Documentation/sound/designs/midi-2.0.rst b/Documentation/sound/designs/midi-2.0.rst index d55b0a4c6acb..27d0d3dea1b0 100644 --- a/Documentation/sound/designs/midi-2.0.rst +++ b/Documentation/sound/designs/midi-2.0.rst @@ -68,6 +68,15 @@ default instead of the MIDI 1.0 interface (at altset 0). You can switch back to the binding with the old MIDI 1.0 interface by passing `midi2_enable=0` option to snd-usb-audio driver module, too. +The USB audio driver tries to query the UMP Endpoint and UMP Function +Block information that are provided since UMP v1.1, and builds up the +topology based on those information. When the device is older and +doesn't respond to the new UMP inquiries, the driver falls back and +builds the topology based on Group Terminal Block (GTB) information +from the USB descriptor. Some device might be screwed up by the +unexpected UMP command; in such a case, pass `midi2_probe=0` option to +snd-usb-audio driver for skipping the UMP v1.1 inquiries. + When the MIDI 2.0 device is probed, the kernel creates a rawmidi device for each UMP Endpoint of the device. Its device name is `/dev/snd/umpC*D*` and different from the standard rawmidi device name @@ -101,11 +110,15 @@ opening `/dev/snd/midiC*D*` will end up with opening the first substream. Each UMP Endpoint can provide the additional information, constructed -from USB MIDI 2.0 descriptors. And a UMP Endpoint may contain one or -more UMP Blocks, where UMP Block is an abstraction introduced in the -ALSA UMP implementations to represent the associations among UMP -Groups. UMP Block corresponds to Group Terminal Block (GTB) in USB -MIDI 2.0 specifications but provide a few more generic information. +from the information inquired via UMP 1.1 Stream messages or USB MIDI +2.0 descriptors. And a UMP Endpoint may contain one or more UMP +Blocks, where UMP Block is an abstraction introduced in the ALSA UMP +implementations to represent the associations among UMP Groups. UMP +Block corresponds to Function Block in UMP 1.1 specification. When +UMP 1.1 Function Block information isn't available, it's filled +partially from Group Terminal Block (GTB) as defined in USB MIDI 2.0 +specifications. + The information of UMP Endpoints and UMP Blocks are found in the proc file `/proc/asound/card*/midi*`. For example:: @@ -207,6 +220,8 @@ The "MIDI 2.0" port is for a UMP Endpoint, and its difference from other UMP Group ports is that UMP Endpoint port sends the events from the all ports on the device ("catch-all"), while each UMP Group port sends only the events from the given UMP Group. +Also, UMP groupless messages (such as the UMP message type 0x0f) are +sent only to the UMP Endpoint port. Note that, although each UMP sequencer client usually creates 16 ports, those ports that don't belong to any UMP Blocks (or belonging @@ -273,6 +288,11 @@ Rawmidi API Extensions The direction is either `SNDRV_UMP_DIR_INPUT`, `SNDRV_UMP_DIR_OUTPUT` or `SNDRV_UMP_DIR_BIDIRECTION`. +* For the device supports UMP v1.1, the UMP MIDI protocol can be + switched via "Stream Configuration Request" message (UMP type 0x0f, + status 0x05). When UMP core receives such a message, it updates the + UMP EP info and the corresponding sequencer clients as well. + Control API Extensions ====================== @@ -337,7 +357,7 @@ Sequencer API Extensions `group_filter` bitmap. The filter consists of bitmap from 1-based Group numbers. For example, when the bit 1 is set, messages from Group 1 (i.e. the very first group) are filtered and not delivered. - The bit 0 is reserved for future use. + The bit 0 is used for filtering UMP groupless messages. * Two new ioctls are added for UMP-capable clients: `SNDRV_SEQ_IOCTL_GET_CLIENT_UMP_INFO` and @@ -349,3 +369,10 @@ Sequencer API Extensions For an Endpoint data, pass 0 to the `type` field, while for a Block data, pass the block number + 1 to the `type` field. Setting the data for a kernel client shall result in an error. + +* With UMP 1.1, Function Block information may be changed + dynamically. When the update of Function Block is received from the + device, ALSA sequencer core changes the corresponding sequencer port + name and attributes accordingly, and notifies the changes via the + announcement to the ALSA sequencer system port, similarly like the + normal port change notification. |