fix: include trailing reserved bytes

[dpezely]

The MIDI 2.0 spec documents could be better about total required number of bytes for each type of message, so it's too easy to miss where 128 bits are required.

• Trailing portions of a MIDI message that are specified as "Reserved" must be included even when all zeros
  • e.g., Set Tempo looks like it should fit within 64 bits but requires 128 bits
• Relevant tests are revised for appending appropriate number of zeroed bytes
• All passed: cargo test --all-targets --all-features
• Appears correct when viewed within MIDI 2.0 Workbench's SMF2 window
  • Albeit, haven't generated a .midi2 file with everything that has changed

Details:

• References to individual sections below are from M2-104-UM
  • Universal MIDI Packet (UMP) Format and MIDI 2.0 Protocol spec
• For a summary with visuals, see "Appendix F: All Defined UMP Formats" and "Appendix G: All Defined Messages"
  • Table 27 4-Byte UMP Formats for Message Type 0x1: System Common & System Real Time
  • Table 32 128 bit UMP Formats for Message Type 0xD: Flex Data Messages
  • Table 33 128 bit UMP Formats for Message Type 0xF: UMP Stream Messages
• However, one table obscures the Reserved portion of some messages
  • Table 34 All Defined Message Formats (in 5 parts)
  • Beware of its rightmost column "Bytes 9-16 (64 bits)" because of portrait to landscape page rotation
• section 7.1 UMP Stream Messages

  • UMP Stream Messages are addressed to the UMP Endpoint, without a Group
    or Channel assignment. All UMP Stream Messages are 128-bit messages [...]

• section 7.4.5 MIDI 2.0 Per-Note Management Message
  • e.g., total bits must be extracted from their diagram

  • | mt=4 | group| 1111 | ch. | r+note# | flags | D | S |
| .... | .... | .... | .... | ....... | ...... | . | . |
| reserved |

• section 7.5.1 Flex Data Messages General Format
  • See first bullet point:

  • A Format field is used to optionally allow a message to have a variable size data, in multiples of 128 bits.

• Similar:
  • 7.5.3 Set Tempo Message
  • 7.5.4 Set Time Signature Message
  • 7.5.5 Set Metronome Message
  • 7.5.6 Example Set Metronome Messages
  • 7.5.7 Set Key Signature Message
• Screenshots from midi2.dev's MIDI 2.0 Workbench SMF2 window: (see below)
  • That's how this issue was discovered
  • MIDI 2.0 Workbench - zeroed reserved bytes.png (with patch)
  • MIDI 2.0 Workbench - malformed midi2 file.png
  • Reserved bytes that should be zero engulfed other messages
  • Malformed at byte offset 20 and 36, thus SMF2 window unable to identify Header / Sequence boundary
  • Images via patched Workbench; see multiple PRs there

TODO — possibly related:

• Table 27 4-Byte UMP Formats for Message Type 0x1: System Common & System Real Time
  • e.g., Tune Request uses 2 bytes with an additional 2 bytes reserved
  • midi2/src/system_common.rs mentions MinSizeUmp(1), MinSizeBytes(2)
  • That parameter for 2 bytes might need to become 4 but needs confirmation

#[midi2_proc::generate_message(
    Via(system_common::SystemCommon),
    FixedSize,
    MinSizeUmp(1),
    MinSizeBytes(2)
)]
struct TuneRequest { /* ... */ }

[BenLeadbetter]

Thanks for the contribution! I'm out of office until the 18th. I'll do a proper review, hotfix, etc after I'm back 😊

[BenLeadbetter]

Looks good to me 👍

Did you already check the remaining messages (unchanged in this PR) against the MIDI 2.0 Workbench app ?

[dpezely]

I've exercised these locally and viewed within MIDI 2.0 Workbench:

• 7.5.3 Set Tempo Message
• 7.5.4 Set Time Signature Message
• 7.5.7 Set Key Signature Message

I probably did a 1-off test with Set Metronome Message but don't recall.

The item marked with TODO is a MIDI feature that I haven't used yet.

[dpezely]

I'll make time to do another quick test for Metronome markings later today to be confirmed via MIDI 2.0 Workbench.

(If you don't have that set up already, it can be a little challenging. See PRs there for Vagrantfile and Dockerfile.)

[dpezely]

Confirmed SetMetronome UMP message bits look correct via MIDI 2.0 Workbench. See second image.

The sequence in that second image:

• byte 64 is Delta Clockstamp with very large value to exercise u20
• byte 68 is Key Signature
• Metronome (values for additional fields are bogus: 1, 2, 3, 4, 5)
• Tempo
• Time Signature

[BenLeadbetter]

Thanks for taking the time to test these!