Add the brief document for describing the MIDI 2.0 implementation on
Linux kernel. Both rawmidi and sequencer API extensions are
described.
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
Documentation/sound/designs/index.rst | 1 +
Documentation/sound/designs/midi-2.0.rst | 342 +++++++++++++++++++++++
2 files changed, 343 insertions(+)
create mode 100644 Documentation/sound/designs/midi-2.0.rst
diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index 1eb08e7bae52..b79db9ad8732 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -15,3 +15,4 @@ Designs and Implementations
oss-emulation
seq-oss
jack-injection
+ midi-2.0
diff --git a/Documentation/sound/designs/midi-2.0.rst b/Documentation/sound/designs/midi-2.0.rst
new file mode 100644
index 000000000000..91634b2fafdc
--- /dev/null
+++ b/Documentation/sound/designs/midi-2.0.rst
@@ -0,0 +1,342 @@
+=================
+MIDI 2.0 on Linux
+=================
+
+General
+=======
+
+MIDI 2.0 is an extended protocol for providing higher resolutions and
+more fine controls over the legacy MIDI 1.0. The fundamental changes
+introduced for supporting MIDI 2.0 are:
+
+- Support of Universal MIDI Packet (UMP)
+- Support of MIDI 2.0 protocol messages
+- Transparent conversions between UMP and legacy MIDI 1.0 byte stream
+- MIDI-CI for property and profile configurations
+
+UMP is a new container format to hold all MIDI protocol 1.0 and MIDI
+2.0 protocol messages. Unlike the former byte stream, it's 32bit
+aligned, and each message can be put in a single packet. UMP can send
+the events up to 16 "UMP Groups", where each UMP Group contain up to
+16 MIDI channels.
+
+MIDI 2.0 protocol is an extended protocol to achieve the higher
+resolution and more controls over the old MIDI 1.0 protocol.
+
+MIDI-CI is a high-level protocol that can talk with the MIDI device
+for the flexible profiles and configurations. It's represented in the
+form of special SysEx.
+
+For Linux implementations, the kernel supports the UMP transport and
+the encoding/decoding of MIDI protocols on UMP, while MIDI-CI is
+supported in user-space over the standard SysEx.
+
+As of this writing, only USB MIDI device supports the UMP and Linux
+2.0 natively. The UMP support itself is pretty generic, hence it
+could be used by other transport layers, although it could be
+implemented differently (e.g. as a ALSA sequencer client), too.
+
+The access to UMP devices are provided in two ways: the access via
+rawmidi device and the access via ALSA sequencer API.
+
+ALSA sequencer API was extended to allow the payload of UMP packets.
+It's allowed to connect freely between MIDI 1.0 and MIDI 2.0 sequencer
+clients, and the events are converted transparently.
+
+
+Kernel Configuration
+====================
+
+The following new configs are added for supporting MIDI 2.0:
+`CONFIG_SND_UMP`, `CONFIG_SND_UMP_LEGACY_RAWMIDI`,
+`CONFIG_SND_SEQ_UMP`, `CONFIG_SND_SEQ_UMP_CLIENT`, and
+`CONFIG_SND_USB_AUDIO_MIDI_V2`. The first visible one is
+`CONFIG_SND_USB_AUDIO_MIDI_V2`, and when you choose it (to set `=y`),
+the core support for UMP (`CONFIG_SND_UMP`) and the sequencer binding
+(`CONFIG_SND_SEQ_UMP_CLIENT`) will be automatically selected.
+
+Additionally, `CONFIG_SND_UMP_LEGACY_RAWMIDI=y` will enable the
+support for the legacy raw MIDI device for UMP Endpoints.
+
+
+Rawmidi Device with USB MIDI 2.0
+================================
+
+When a device supports MIDI 2.0, the USB-audio driver probes and uses
+the MIDI 2.0 interface (that is found always at the altset 1) as
+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.
+
+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
+`/dev/snd/midiC*D*` for MIDI 1.0, in order to avoid confusing the
+legacy applications accessing mistakenly to UMP devices.
+
+You can read and write UMP packet data directly from/to this UMP
+rawmidi device. For example, reading via `hexdump` like below will
+show the incoming UMP packets of the card 0 device 0 in the hex
+format::
+
+ % hexdump -C /dev/snd/umpC0D0
+ 00000000 01 07 b0 20 00 07 b0 20 64 3c 90 20 64 3c 80 20 |... ... d<. d<. |
+
+Unlike the MIDI 1.0 byte stream, UMP is a 32bit packet, and the size
+for reading or writing the device is also aligned to 32bit (which is 4
+bytes).
+
+The 32-bit words in the UMP packet payload are always in CPU native
+endianness. Transport drivers are responsible to convert UMP words
+from / to system endianness to required transport endianness / byte
+order.
+
+When `CONFIG_SND_UMP_LEGACY_RAWMIDI` is set, the driver creates
+another standard raw MIDI device additionally as `/dev/snd/midiC*D*`.
+This contains 16 substreams, and each substream corresponds to a
+(0-based) UMP Group. Legacy applications can access to the specified
+group via each substream in MIDI 1.0 byte stream format. With the
+ALSA rawmidi API, you can open the arbitrary substream, while just
+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.
+The information of UMP Endpoints and UMP Blocks are found in the proc
+file `/proc/asound/card*/midi*`. For example::
+ % cat /proc/asound/card1/midi0
+ ProtoZOA MIDI
+
+ Type: UMP
+ EP Name: ProtoZOA
+ EP Product ID: ABCD12345678
+ UMP Version: 0x0000
+ Protocol Caps: 0x00000100
+ Protocol: 0x00000100
+ Num Blocks: 3
+
+ Block 0 (ProtoZOA Main)
+ Direction: bidirection
+ Active: Yes
+ Groups: 1-1
+ Is MIDI1: No
+
+ Block 1 (ProtoZOA Ext IN)
+ Direction: output
+ Active: Yes
+ Groups: 2-2
+ Is MIDI1: Yes (Low Speed)
+ ....
+
+Note that `Groups` field shown in the proc file above indicates the
+1-based UMP Group numbers (from-to).
+
+Those additional UMP Endpoint and UMP Block information can be
+obtained via the new ioctls `SNDRV_UMP_IOCTL_ENDPOINT_INFO` and
+`SNDRV_UMP_IOCTL_BLOCK_INFO`, respectively.
+
+The rawmidi name and the UMP Endpoint name are usually identical, and
+in the case of USB MIDI, it's taken from `iInterface` of the
+corresponding USB MIDI interface descriptor. If it's not provided,
+it's copied from `iProduct` of the USB device descriptor as a
+fallback.
+
+The Endpoint Product ID is a string field and supposed to be unique.
+It's copied from `iSerialNumber` of the device for USB MIDI.
+
+The protocol capabilities and the actual protocol bits are defined in
+`asound.h`.
+
+
+ALSA Sequencer with USB MIDI 2.0
+================================
+
+In addition to the rawmidi interfaces, ALSA sequencer interface
+supports the new UMP MIDI 2.0 device, too. Now, each ALSA sequencer
+client may set its MIDI version (0, 1 or 2) to declare itself being
+either the legacy, UMP MIDI 1.0 or UMP MIDI 2.0 device, respectively.
+The first, legacy client is the one that sends/receives the old
+sequencer event as was. Meanwhile, UMP MIDI 1.0 and 2.0 clients send
+and receive in the extended event record for UMP. The MIDI version is
+seen in the new `midi_version` field of `snd_seq_client_info`.
+
+A UMP packet can be sent/received in a sequencer event embedded by
+specifying the new event flag bit `SNDRV_SEQ_EVENT_UMP`. When this
+flag is set, the event has 16 byte (128 bit) data payload for holding
+the UMP packet. Without the `SNDRV_SEQ_EVENT_UMP` bit flag, the event
+is treated as a legacy event as it was (with max 12 byte data
+payload).
+
+With `SNDRV_SEQ_EVENT_UMP` flag set, the type field of a UMP sequencer
+event is ignored (but it should be set to 0 as default).
+
+The type of each client can be seen in `/proc/asound/seq/clients`.
+For example::
+ % cat /proc/asound/seq/clients
+ Client info
+ cur clients : 3
+ ....
+ Client 14 : "Midi Through" [Kernel Legacy]
+ Port 0 : "Midi Through Port-0" (RWe-)
+ Client 20 : "ProtoZOA" [Kernel UMP MIDI1]
+ UMP Endpoint: ProtoZOA
+ UMP Block 0: ProtoZOA Main [Active]
+ Groups: 1-1
+ UMP Block 1: ProtoZOA Ext IN [Active]
+ Groups: 2-2
+ UMP Block 2: ProtoZOA Ext OUT [Active]
+ Groups: 3-3
+ Port 0 : "MIDI 2.0" (RWeX) [In/Out]
+ Port 1 : "ProtoZOA Main" (RWeX) [In/Out]
+ Port 2 : "ProtoZOA Ext IN" (-We-) [Out]
+ Port 3 : "ProtoZOA Ext OUT" (R-e-) [In]
+
+Here you can find two types of kernel clients, "Legacy" for client 14,
+and "UMP MIDI1" for client 20, which is a USB MIDI 2.0 device.
+A USB MIDI 2.0 client gives always the port 0 as "MIDI 2.0" and the
+rest ports from 1 for each UMP Group (e.g. port 1 for Group 1).
+In this example, the device has three active groups (Main, Ext IN and
+Ext OUT), and those are exposed as sequencer ports from 1 to 3.
+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.
+
+Note that, although each UMP sequencer client usually creates 16
+ports, those ports that don't belong to any UMP Blocks (or belonging
+to inactive UMP Blocks) are marked as inactive, and they don't appear
+in the proc outputs. In the example above, the sequencer ports from 4
+to 16 are present but not shown there.
+
+The proc file above shows the UMP Block information, too. The same
+entry (but with more detailed information) is found in the rawmidi
+proc output.
+
+When clients are connected between different MIDI versions, the events
+are translated automatically depending on the client's version, not
+only between the legacy and the UMP MIDI 1.0/2.0 types, but also
+between UMP MIDI 1.0 and 2.0 types, too. For example, running
+`aseqdump` program on the ProtoZOA Main port in the legacy mode will
+give you the output like::
+
+ % aseqdump -p 20:1
+ Waiting for data. Press Ctrl+C to end.
+ Source Event Ch Data
+ 20:1 Note on 0, note 60, velocity 100
+ 20:1 Note off 0, note 60, velocity 100
+ 20:1 Control change 0, controller 11, value 4
+
+When you run `aseqdump` in MIDI 2.0 mode, it'll receive the high
+precision data like::
+
+ % aseqdump -u 2 -p 20:1
+ Waiting for data. Press Ctrl+C to end.
+ Source Event Ch Data
+ 20:1 Note on 0, note 60, velocity 0xc924, attr type = 0, data = 0x0
+ 20:1 Note off 0, note 60, velocity 0xc924, attr type = 0, data = 0x0
+ 20:1 Control change 0, controller 11, value 0x2000000
+
+while the data is automatically converted by ALSA sequencer core.
+
+
+Rawmidi API Extensions
+======================
+
+* The additional UMP Endpoint information can be obtained via the new
+ ioctl `SNDRV_UMP_IOCTL_ENDPOINT_INFO`. It contains the associated
+ card and device numbers, the bit flags, the protocols, the number of
+ UMP Blocks, the name string of the endpoint, etc.
+
+ The protocols are specified in two field, the protocol capabilities
+ and the current protocol. Both contain the bit flags specifying the
+ MIDI protocol version (`SNDRV_UMP_EP_INFO_PROTO_MIDI1` or
+ `SNDRV_UMP_EP_INFO_PROTO_MIDI2`) in the upper byte and the jitter
+ reduction timestamp (`SNDRV_UMP_EP_INFO_PROTO_JRTS_TX` and
+ `SNDRV_UMP_EP_INFO_PROTO_JRTS_RX`) in the lower byte.
+
+ A UMP Endpoint may contain up to 32 UMP Blocks, and the number of
+ the currently assigned blocks are shown in the Endpoint information.
+
+* Each UMP Block information can be obtained via another new ioctl
+ `SNDRV_UMP_IOCTL_BLOCK_INFO`. The block ID number (0-based) has to
+ be passed for the block to query. The received data contains the
+ associated the direction of the block, the first associated group ID
+ (0-based) and the number of groups, the name string of the block,
+ etc.
+
+ The direction is either `SNDRV_UMP_DIR_INPUT`,
+ `SNDRV_UMP_DIR_OUTPUT` or `SNDRV_UMP_DIR_BIDIRECTION`.
+
+
+Control API Extensions
+======================
+
+* The new ioctl `SNDRV_CTL_IOCTL_UMP_NEXT_DEVICE` is introduced for
+ querying the next UMP rawmidi device, while the existing ioctl
+ `SNDRV_CTL_IOCTL_RAWMIDI_NEXT_DEVICE` queries only the legacy
+ rawmidi devices.
+
+ For setting the subdevice (substream number) to be opened, use the
+ ioctl `SNDRV_CTL_IOCTL_RAWMIDI_PREFER_SUBDEVICE` like the normal
+ rawmidi.
+
+
+Sequencer API Extensions
+========================
+
+* `midi_version` field is added to `snd_seq_client_info` to indicate
+ the current MIDI version (either 0, 1 or 2) of each client.
+ When `midi_version` is 1 or 2, the alignment of read from a UMP
+ sequencer client is also changed from the former 28 bytes to 32
+ bytes for the extended payload. The alignment size for the write
+ isn't changed, but each event size may differ depending on the new
+ bit flag below.
+
+* `SNDRV_SEQ_EVENT_UMP` flag bit is added for each sequencer event
+ flags. When this bit flag is set, the sequencer event is extended
+ to have a larger payload of 16 bytes instead of the legacy 12
+ bytes, and the event contains the UMP packet in the payload.
+
+* The new sequencer port type bit (`SNDRV_SEQ_PORT_TYPE_MIDI_UMP`)
+ indicates the port being UMP-capable.
+
+* The sequencer ports have new capability bits to indicate the
+ inactive ports (`SNDRV_SEQ_PORT_CAP_INACTIVE`) and the UMP Endpoint
+ port (`SNDRV_SEQ_PORT_CAP_UMP_ENDPOINT`).
+
+* The event conversion of ALSA sequencer clients can be suppressed the
+ new filter bit `SNDRV_SEQ_FILTER_NO_CONVERT` set to the client info.
+ For example, the kernel pass-through client (`snd-seq-dummy`) sets
+ this flag internally.
+
+* The port information gained the new field `direction` to indicate
+ the direction of the port (either `SNDRV_SEQ_PORT_DIR_INPUT`,
+ `SNDRV_SEQ_PORT_DIR_OUTPUT` or `SNDRV_SEQ_PORT_DIR_BIDIRECTION`).
+
+* Another additional field for the port information is `ump_group`
+ which specifies the associated UMP Group Number (1-based).
+ When it's non-zero, the UMP group field in the UMP packet updated
+ upon delivery to the specified group (corrected to be 0-based).
+ Each sequencer port is supposed to set this field if it's a port to
+ specific to a certain UMP group.
+
+* Each client may set the additional event filter for UMP Groups in
+ `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.
+
+* Two new ioctls are added for UMP-capable clients:
+ `SNDRV_SEQ_IOCTL_GET_CLIENT_UMP_INFO` and
+ `SNDRV_SEQ_IOCTL_SET_CLIENT_UMP_INFO`. They are used to get and set
+ either `snd_ump_endpoint_info` or `snd_ump_block_info` data
+ associated with the sequencer client. The USB MIDI driver provides
+ those information from the underlying UMP rawmidi, while a
+ user-space client may provide its own data via `*_SET` ioctl.
+ 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.
--
2.35.3
