So the MIDI 2.0 spec just dropped and I'm skimming it. Highlights: - New layer above everything called UMP wrapping both old MIDI 1.0 messages and new stuff. - New addressing level of 16 groups on top of channels. So now one stream carries 16 "mega-channels" of 16ch each.
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Now the thing is the new UMP packet format does not define any mapping to physical transports, and AFAICT the negotiation is between MIDI1/MIDI2 features, not the underlying transport. So how is UMP defined over e.g. existing USB-MIDI or DIN UART MIDI transports? No idea.
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It seems no physical layer mappings are defined in the MIDI 2.0 spec itself, that's for another document to lay out including any negotiation.
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According to their website, they're focusing on USB first (I guess the old 31kbit UART transport is deprecated, unsurprisingly), and a new mapping for UMP over USB(-audio?) needs to be written before that works. So no automatic backwards compat with MIDI1 byte streams.
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One thing they did do is make the UMP format self-delimiting. The message type alone determines message length, and they arbitrarily pre-assigned some lengths to all the unused message types. So transports should be able to deliver UMP messages with future expansions cleanly.
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OTOH it is *not* robust at the 32bit word level, so the underlying transport has to guarantee that. If you drop or corrupt a word expect things to explode.
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(MIDI1 was slightly better at this with the start/continue markers, but in practice this was useless anyway because as soon as you drop any data you get stuck notes so you're screwed anyway)
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Oh yeah, another fix: 7-bit sysex messages are still atomic (except for realtime messages) to preserve MIDI 1.0 compat, but the new 8-bit sysex messages *are* interleavable with other messages and even up to 256 sysex messages may be interleaved together in streams.
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