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Re: [Libcdio-devel] OpenBSD vs libcdio vs Audacious

From: Thomas Schmitt
Subject: Re: [Libcdio-devel] OpenBSD vs libcdio vs Audacious
Date: Sun, 27 Jan 2019 17:18:52 +0100


> cmd: be 00 00 00 00 00 00 00 25 78 | datalen = 87024

The datalen is suspiciously high.

> Is there perhaps some constraint on the transfer length? Must it be an even
> number, or a power of two, for example?

The operating system SCSI passthrough facilities have limits for a single
transfer. (The drives may have too.)
With CD and DVD you can surely expect up to 32 KiB. With BD it's 64 KiB
(or else no fast streaming).

> Did I say bits? It's probably bytes.

37 sectors of 2352 bytes.

Odd numbers of sectors are OK. cdrecord with CD uses 0x1F = 31 sectors
with command WRITE(10). Further:  At the end of a CD or DVD DAO run,
arbitrary small numbers of sectors have to be written to exactly fit the

> cmd: be 00 00 00 00 00 00 00 12 78 | datalen = 42336

It then repeats the READ CD command at the same address (sector 0) but
requesting only 18 sectors. This seems to succeed.
Then it goes on with steps of 0x12 = 18 sectors.
So all sectors got read. None were skipped.

This all looks like a calibration attempt to determine the permissible
size of a transaction. (Once per track could make sense with mixed
mode CD where sector sizes vary from track to track.)

Have a nice day :)


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