Hi Clemens and others, Any thoughts on this? I would like to start working on it.
On 30/09/16 21:32, Felipe Ferreri Tonello wrote: > 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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