Re: RTP-MIDI strange field masks?

[Evan Huus <eapache () gmail com>]

I haven’t actually looked at the code, so it’s possible we’re doing the
masking but not actually combining the bits into a single 14-bit value
properly still. I wouldn’t expect a simple mask value to accomplish that.

Evan

On Thu, Jul 8, 2021 at 14:32 Evan Huus <eapache () gmail com> wrote:

> Based on the 0xxxxxxx of your example and references like [1], I believe
> the masks are correct. MIDI seems to mostly use seven bit bytes schmucked
> together for some reason, so ignoring the high bit of each byte seems
> correct to me.
>
> Evan
>
> [1] http://midi.teragonaudio.com/tech/midispec/wheel.htm
>
> On Thu, Jul 8, 2021 at 13:58 Martin Mathieson via Wireshark-dev <
> wireshark-dev () wireshark org> wrote:
>
> > These mask fields (0x7f7f, 0x7f7f7f7f, etc) look wrong to me, but I am
> > worried I might be missing something?
> > Looking at an example in RFC 4695 (Song Position Pointer) I think this
> > (on page 157) is saying that is it just a 2-byte field (and should
> > therefore have a non-mask of 0x0)?
> >
> > | Song Position Pointer          | 11110010 0xxxxxxx 0yyyyyyy |
> >
> >
> > These warnings are from ./tools/check_typed_item_calls.py --mask
> >
> >
> > Warning:  epan/dissectors/packet-rtp-midi.c filter= rtpmidi.deltatime_2
> >  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter= rtpmidi.deltatime_3
> >  - mask with non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter= rtpmidi.deltatime_4
> >  - mask with non-contiguous bits 0x7f7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter= rtpmidi.pitch_bend  -
> > mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sj_chapter_x_first_2  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sj_chapter_x_first_3  - mask with non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sj_chapter_x_first_4  - mask with non-contiguous bits 0x7f7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.song_position_pointer  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_general_information_device_family  - mask
> > with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_general_information_device_family_member
> >  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_general_information_software_revision  -
> > mask with non-contiguous bits 0x7f7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_sample_number  - mask with
> > non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_sample_period  - mask with
> > non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_sample_length  - mask with
> > non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_loop_start  - mask with
> > non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_loop_end  - mask with
> > non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_sample_dump_lp_trans_ln  - mask with
> > non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_non_realtime_fd_length  - mask with non-contiguous
> > bits 0x7f7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_tune_freq  - mask with non-contiguous bits 0x7f7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_rt_ni_barnum  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_rt_dc_volume  - mask with non-contiguous bits 0x7f7f
> > Warning:  epan/dissectors/packet-rtp-midi.c filter=
> > rtpmidi.sysex_common_rt_dc_balance  - mask with non-contiguous bits 0x7f7f
> >
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