Hi Clemens, On 30/09/16 19:46, Clemens Ladisch wrote: > Felipe Ferreri Tonello wrote: >> This event we are discussing is time based. >> The only difference is that the event time is not its delivered time, >> but some time in the past. >> >> I just want to make ALSA Sequencer support this idea, which is new and a >> requirement for MIDI over BLE to work properly. > > I see no such requirement in the BLE-MIDI specification, which says: > | To maintain precise inter-event timing, this protocol uses 13-bit > | millisecond-resolution timestamps to express the render time and event > | spacing of MIDI messages. > and: > | Correlation between the receiver’s clock and the received timestamps > | must be performed to ensure accurate rendering of MIDI messages, and > | is not addressed in this document. > > In the context of the ALSA sequencer, "rendering" means delivery.
Yes, the correlation exists on the current implementation I am working on[1]. The problem is the latency on receiving BLE packets. The timestamp the device sends and the "receiver's clock" (ALSA Seq) will very quickly get out-of-sync, causing this timestamp to be invalid. Thus we need somehow to set the event timestamp to any arbitrary value, in practice it will be the BLE-MIDI timestamps (normalized to the central timestamp, of course). [1] https://github.com/ftonello/bluez/blob/midi/profiles/midi/midi.c#L138 -- Felipe
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