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List:       linux-bluetooth
Subject:    Re: [PATCH BlueZ] profiles/midi: Added MIDI over BLE profile implementation
From:       Luiz Augusto von Dentz <luiz.dentz () gmail ! com>
Date:       2016-11-29 12:25:07
Message-ID: CABBYNZK4_mQ0nAEbR1he2YK2iUkJHagE68Xej8xNy+3U-Z0rOA () mail ! gmail ! com
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Hi Felipe,

On Tue, Nov 29, 2016 at 2:19 PM, Felipe Ferreri Tonello
<eu@felipetonello.com> wrote:
> Hi all,
> 
> Ping on this?
> 
> I already have a v2 ready but waiting for more comments to send.
> 
> More comments below.
> 
> On 21/11/16 12:25, Felipe Ferreri Tonello wrote:
> > Hi Luiz,
> > 
> > On November 21, 2016 11:47:04 AM GMT+00:00, Luiz Augusto von Dentz \
> > <luiz.dentz@gmail.com> wrote:
> > > Hi Felipe,
> > > 
> > > On Mon, Nov 21, 2016 at 1:21 PM, Felipe Ferreri Tonello
> > > <eu@felipetonello.com> wrote:
> > > > Hi all,
> > > > 
> > > > On 18/11/16 14:59, Felipe F. Tonello wrote:
> > > > > This plugin implements the Central roli of MIDI over Bluetooth
> > > > > Low-Energy (BLE-MIDI) 1.0 specification as published by MMA in
> > > > > November/2015.
> > > > > 
> > > > > It was implmemented as a bluez plugin because of latency
> > > requirements
> > > > > of MIDI. There are still room for improvements on this regard.
> > > > > 
> > > > > Since all parsing and state-machine code is in libmidi.[hc] it
> > > should be
> > > > > simple to implement Peripheral role as a GATT service as well.
> > > > > 
> > > > > I have also implemented several unit-tests that can be easily
> > > extended
> > > > > without adding any code, just use-cases.
> > > > > 
> > > > > Files added:
> > > > > * profiles/midi/midi.c: Actual GATT plugin
> > > > > * profiles/midi/libmidi.[ch]: MIDI parsers
> > > > > * unit/test-midi.c: Unit-tests
> > > 
> > > Btw, usually we stayed away from alsa/audio dependencies since they
> > > are quite time sensitive which may impact in the responsiveness of
> > > bluetoothd, so I wonder if you document anything in this regard? Also
> > > please keep in mind many parts of bluetoothd are not thread-safe so if
> > > there are other threads involved Im afraid we won't be taking more
> > > than the GATT plugin leaving the remaining code to be done somewhere
> > > else.
> > 
> > Yes, this is time sensitive, as it requires low-latency connection intervals, but \
> > I didn't notice any problems with it. I have tested with two devices connected at \
> > the same time and it works very well. What sort of document are you referring to? \
> > As this profile is quite unique in terms of low-latency GATT services it may be \
> > interesting to optimise it in future if necessary. 
> > On the thread note, I was aware of this and implemented in a way thst doesn't \
> > require any extra threads.
> 
> This plugin doesn't require any new threads. It relies on notifications
> from a device to parse and render proper events that are queued in the
> kernel, causing no blocks at all. Even if an error occur, it will be
> handled and returned control to bluetoothd.
> 
> It also adds a new file descriptor to be read using struct io. That is
> necessary to read events from applications and render raw BLE packets to
> be sent to the device with a write without response command. It doesn't
> block as well.
> 
> Even though this adds a new dependency, ALSA, it is not an audio plugin.
> It is rather a MIDI plugin, which is a byte stream protocol with low
> throughput but requires low-latency.

Please add this to the commit message of the v2, I will be checking
for other problems when applying it.

Luiz Augusto von Dentz
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