Re: ISO file format vs. SCSI CD model
- From: "swansnow" <corinna.schultz@xxxxxxxxx>
- Date: 13 Jun 2006 09:03:57 -0700
I want to write a program (or driver, or module, I haven't decided) to
emulate a CD drive (RW), but using a file as the device, and I'm
thinking about what kind of file formats are used. I don't know too
much about this -- I'm still educating myself. I've read through the
MMC and SAM docs, and some other stuff.
The two options I'm thinking of are: how to emulate a CD drive if I
start with an empty file, and how to do it if I start with an ISO
image. I want to be able to read and write. Currently, I'm not
considering the possibility of burning the file back onto a CD. Though
if I keep the ISO file format, I suppose writing back to a physcial CD
would be easy.
(This idea is kind of like the loopback mount you can do in Linux, but
I don't want to look at that code :) )
Grant Edwards wrote:
The ISO file only contains the "payload".
I suspect that generating the ISO file unencodes the 8-to-14 encoding
and error-correction (that happens at the device level?) Does it also
de-interleave the frames, and remove the sync bytes?
But still, how do you resolve LBA addresses, or track numbers?
Does an ISO file contain the iso filesystem (with a table of contents
at the beginning and so forth)?
Don't the standards you've looked at specify how a 2K block of
"user" data is encoded on the disk surface?
Yes, there is some metadata that is present in the user data area of a
disc, and it's unclear to me what happens to it when an ISO is made.
Why does it matter unless you're actually designing drive electronics?
(See above - I'm wanting to write an emulator)
So then when you rip an ISO image (to, say, play a game without having
the physical CDs) the ripping software does a lot of stuff behind the
scenes? I've seen people say that you can get an iso image by using dd
-- does that mean that dd doesn't just copy bytes from the device? Or
perhaps, the device driver only returns user data to dd's request for
bytes?
And then when you burn an iso image to a CD, all that metadata is added
back in?
I have a lot of questions, I know... :-)
I know just enough to be confused. Thanks for your help.
-Corinna
.
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