SET READ AHEAD and READ_CD

keiji_katata at post.pioneer.co.jp keiji_katata at post.pioneer.co.jp
Mon Aug 18 00:17:58 PDT 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* keiji_katata at post.pioneer.co.jp
*

Hi Henry,

SET READ AHEAD command is designed for DVD Video playback. DVD Video has
some trick play e.g. multi-angle playback. Old DVD ROM drive had heavy
pick-up head and slow 1X read speed (11.08Mb/s). So to skip different angle
data, SET READ AHEAD command was born. Currently SET READ AHEAD command is
useless. Because DVD ROM drive has 2X or higher data read speed.

I think there are 3 different types of drive.

Type 1: The drive does not support SET READ AHEAD command.
Type 2: The drive supports SET READ AHEAD command only for READ10, READ12
or only for DVD.
Type 3: The drive supports SET READ AHEAD command for all cases.

I think many of DVD-ROM drives are type 1. There are 2 reasons. Reason 1:
DVD-ROM data read speed is 2X or higher, then no DVD playback software uses
SET READ AHEAD command for DVD Video playback. Reason 2: DVD-ROM drive
decoder IC can not support SET READ AHEAD command. Low cost DVD-ROM drive
uses decoder IC auto-decode to read CD/DVD disc. Those ICs can handle
single ring buffer, so they can not support discontinuity of buffered data.

Type 2 is my implementation. So for CD DA playback, SET READ AHEAD setting
is ignored.

Many current and future drives may not support SET READ AHEAD command for
CD-DA playback.
Why do you need SET READ AHEAD command? What is "optimize audio playback"?
Between Track and Track, CD-DA has 2 seconds silent gap. Drive seek may be
done less than 0.3 sec. If playback software has 1 min. of audio data
buffer, drive has 4X CAV or higher speed usually, audience should not have
any silent time without actual silence.

Keiji Katata
PIONEER CORP.





"Henry Gabryjelski" <henrygab at windows.microsoft.com>@avc-pioneer.com on
2003/08/16 01:30:02

mtfuji5 at avc-pioneer.com$B$KJV?.$7$F$/$@$5$$(J

$BAw?.<T(J:     owner-mtfuji5 at avc-pioneer.com




$B08 at h(J:  <mtfuji5 at avc-pioneer.com>, <T10 at t10.org>
cc:
bcc:
$B7oL>(J:  SET READ AHEAD and  READ_CD



If a drive is reading audio from a CD track (let's say 2744 bytes/sector
for
audio, C2, and subcode data) using READ_CD, and receives a SET READ AHEAD
command (to skip a track of audio, for example), will current market drives
perform at least as well as if this command was not sent?

Also, for future drives, would it be difficult to implement support for
this
type of command sequence to help optimize audio playback?

This would, in conjunction with a CD speed selection process, allow for
much
slower media spin rates while still playing audio CDs; This is important
for
many reasons, such as workplace noise regulations for various countries.

Thanks,
.








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