Misc notes==========- **MPU401 kernel module.** If your soundcard supports MIDI input andoutput, chances are that it is powered by an MPU401 chip. Becausethis interface is so popular, BeOS comes with a kernel module thatmakes it easy to write drivers for the MPU401. Thanks to Greg Crain,we now have an open source version of this kernel module.The mpu401 module lives in ``src/add-ons/kernel/generic/mpu401``. Itsupports both the v1 and (undocumented) v2 protocols, although v2 isnot complete since we don't really know how it works. Unfortunately,almost no existing drivers use v1; most of the drivers provided by Berequire v2. Currently, the module returns B_ERROR when a MIDI deviceis opened with v2.For an example on how to use the MPU401 module in your own driver,see the source code for the "emuxki" driver elsewhere in the sourcetree.- **Clients without a BApplication.** Sometimes the midi_server's debugoutput shows an "Application -1 not registered" error message. Thismeans it cannot figure out which app an incoming BMessage came from.The server ignores those messages.How can this happen? libmidi2 has two ways of sending messages to themidi_server: it either expects a reply back or not. In the firstcase, it is obvious to the midi_server what the reply address of themessage is. In the second case, even though it is not necessary forthe server to send a message back, it still uses the reply address todetermine which app the message came from. For this, BMessenger usesbe_app_messenger of the client app.However, if the client app has no BApplication object, there is nobe_app_messenger either. Now, the midi_server cannot determine wherethe message came from and will ignore it. Is this important? Forexample, when such a client app Release()'s its endpoints, it sends amessage to the server without a return address. Now the serverignores that message and does not remove the endpoint from theroster. Of course, after the client app has died, the endpoints willbe removed eventually. Does all of this matter? Not really, becauseonly trivial apps will have no BApplication object.