30 Sep
2016
30 Sep
'16
10:32 p.m.
Hi Clemens,
On 30/09/16 19:46, Clemens Ladisch wrote:
Felipe Ferreri Tonello wrote:
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
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.