From: Ronan Farrell (rfarrell at domain parthus.com)
Date: Thu 25 May 2000 - 17:59:04 IST
> > What's a CDRW us a DSP for?
> Not sure, actually. Generating laser pulses ?
More likely they are used to do some of the channel filtering and
pre-emphasis that is necessary in constructing the signal for use in
both timing the laser pulse, but also the position of the drive head
on the disk. There are rules that are used when saving data to
hard-disks/CDR's to facilitate signal reconstruction, for example
maximum number of 1's or 0's in a row. It is probably also used in the
read channel for signal reconstruction. Some modern drives keep the
drive rotating at constant angular velocity rather than linear velocity
and hence need to do on the fly frequency stretching/compacting of the
data on the fly.
A DSP chip is in many ways nothing more than an extremely fast
number-crunching processor. Any task that requires intensive processing
but also needs programmability will need a DSP chip. The trade-off is
usually custom hardware (fast but long-time to develop) vs off-the-shell
cpu's (slower but quicker to develop).
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