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Midi2 | System Exclusive 8 Messages | Unexpected End of Data

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Ben
 Ben
Posts: 1
New Member
Topic starter
 

Hi,

I've got an issue with the universal midi packet spec (M2-104-UM_v1-0_UMP_and_MIDI_2-0_Protocol_Specification) in the System Exclusive 8 Messages, Unexpected End of Data specification.

4.5.1 Unexpected End of Data
If the Sender runs out of payload data before sending a System Exclusive 8 End UMP, then the Sender shall send a System Exclusive 8 End UMP with all data bytes set to zero, and the # of bytes field set to either of the two following values:
• 0x1 if the Sender knows that the previous data in the SysEx8 message is valid.
• 0xF if the previous data is an incomplete message, or if the resulting quality of previous data is unknown.

But it also states just above:

# of bytes
This 4-bit field declares the number of valid data bytes in each UMP, starting from and including the Stream ID through to the end of the 128-bit UMP (i.e., 1 to 14 bytes). Stream ID is mandatory (1 byte), so a value of 0x0 is not valid in the # of bytes field.

This would make it impossible to send an ordinary System Exclusive 8 End UMP message containing no data with stream id 0x0. Such a message would be read as an unexpected end of data message (with previously sent data valid).

Is this intended?

 
Posted : 02/11/2022 10:12 am
Eddie Lotter
Posts: 295
Reputable Member
 

[quotePost id=16455]This would make it impossible to send an ordinary System Exclusive 8 End UMP message containing no data with stream id 0x0. Such a message would be read as an unexpected end of data message (with previously sent data valid).

Is this intended?[/quotePost]
My reading of the spec is that an "ordinary" SysEx8 End UMP will never have no data. If it does, then it is, by definition, not "ordinary".
Can you describe a scenario where you would want to send an "ordinary" SysEx8 End UMP with no data?

 
Posted : 02/11/2022 12:22 pm
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