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        MIDI-OX >> Questions and Discussion >> USB MIDI Devices and SysEx using MS Drivers
        
(Message started by: Jamie OConnell on Mar 27^th, 2008, 2:45pm)

Title: USB MIDI Devices and SysEx using MS Drivers
Post by Jamie OConnell on Mar 27^th, 2008, 2:45pm

Other manufacturers use the MS Port Class driver as well. There are several known problems transmitting SysEx buffers using this driver (not sure why Microsoft does not fix it?). A rudimentary Google search turns up the following:

The Microsoft driver isn't multiclient capable. This means, that only one program can allocate a MIDI port at the same time.
The Microsoft driver isn't able to send one SysEx string which is distributed over multiple buffers without errors. The complete SysEx string has to be sent from a single buffer (this affects the MIOS download, in the MIDI-OX port config menu, you have to increase the Low level Output buffer size from 256 to 2048).

Method to Test a MIDI interface using a Hardware Loopback

A) Take a MIDI cable and attach the MIDI Interface Output port to the MIDI Interface Input port. If you have an interface with two Male MIDI plugs, get a double female adapter to allow the connection.
B) Open the Port as both Input and Output in MIDI-OX
C) Ensure "Pass SysEx" is checked in MIDI-OX Options Menu.
D) Open the SysEx view (View | SysEx...)
E) Open a large SysEx dump file (.syx) in the SysEx Command Window (Command Window | Load File...)
F) Choose: Command Window | Send/Receive SysEx
G) When the dump finishes, choose: SysEx | Compare Windows

If the Windows are not identical there is corruption introduced during transmission.