Remove duplicate CD modes #12012
Remove duplicate CD modes #12012
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| else if (!strcmp(typestring, "MODE2/2336")) | ||
| { | ||
| *trktype = CD_TRACK_MODE2_FORM_MIX; | ||
| *datasize = 2336; | ||
| } |
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I get that this code is unreachable so this won’t change behaviour, but what’s it supposed to be doing? The place where it actually catches this is at line 630:
else if (!strcmp(typestring, "MODE2/2336"))
{
*trktype = CD_TRACK_MODE2;
*datasize = 2336;
}It gives CD_TRACK_MODE2_FORM_MIX. Why is it trying to use CD_TRACK_MODE2_FORM_MIX for the same track type here?
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I have a strong feeling that this was a slip of the mind type of mistake. Looking at the original commit that introduced the two MODE2/2336s, it looks like they just added a corresponding MODEx/y for all of the existing .toc type strings.
.toc defines both MODE2 and MODE2_FORM_MIX, and both also are defined as 2336 bytes per sector.
"The block length of the input data depends on the : AUDIO: 2352 bytes (588 samples), MODE1: 2048 bytes, MODE1_RAW: 2352 bytes, MODE2: 2336 bytes, MODE2_FORM1: 2048 bytes, MODE2_FORM2: 2324 bytes, MODE2_FORM_MIX: 2336 bytes including the sub-header, MODE2_RAW: 2352 bytes."
source: https://manpages.ubuntu.com/manpages/focal/en/man1/cdrdao.1.html
CD_TRACK_MODE2_FORM_MIX is like a meta type. It means the track is either MODE2_FORM1 or MODE2_FORM2, padded to the same block size and has the sub-header included in the 2336 bytes. MODE2_FORM1's user data size is 2048 bytes and MODE2_FORM2's user data size is 2328 bytes. The subheader for both form 1 and form 2 is 8 bytes.
CD_TRACK_MODE2 means it's 2336 bytes of just user data (no headers).
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Right, CD_TRACK_MODE2 is the CD-ROM Mode 2 data track format, with 2,336 bytes of data per sector, and no additional error detection/correction data.
But do CD_TRACK_MODE2_FORM1 and CD_TRACK_MODE2_FORM2 really make sense? The whole point of CD-ROM XA tracks is that they can contain a mixture of Form 1 and Form 2 sectors (with and without additional error correction data, respectively). Or are these “artificial” formats for authoring, where the software interpreting the data is expected to generate a track containing only a single form?
And why would there be padding in a CD_TRACK_MODE2_FORM_MIX track? The sector payload size is the same for both forms. Form 1 is 8-byte subheader, 2,048-byte data, 4-byte checksum, 276-byte ECC = 2,336 bytes total. Form 2 is 8-byte subheader, 2,324-byte data, 4-byte checksum = 2,336 bytes total. Or is there some weirdess where the checksum and ECC bytes are treated as “padding” and replaced with the appropriate calculated content?
src/lib/util/cdrom.cpp
Outdated
| else if (!strcmp(typestring, "MODE2/2352")) | ||
| { | ||
| *trktype = CD_TRACK_MODE2_RAW; | ||
| *datasize = 2352; | ||
| } |
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There’s no other place that catches MODE2/2352 so it isn’t a duplicate. Why did you remove it?
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oh sorry i confused it with MODE1/2352
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I've read the ISO9660 spec and I can't find a mention of a mixed form Mode2 track, can we get someone who is familiar with CDI and Dreamcast discs in here? |
It has nothing to do with Dreamcast – it’s CD-ROM XA. The Philips spec is easy enough to find. |
Resolves #9084