l i n u x - u s e r s - g r o u p - o f - d a v i s
L U G O D
 
Next Meeting:
October 7: Social gathering
Next Installfest:
TBD
Latest News:
Aug. 18: Discounts to "Velocity" in NY; come to tonight's "Photography" talk
Page last updated:
2006 Jan 27 17:20

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

Report this post as spam:

(Enter your email address)
Re: [vox-tech] update on the audio CD problem
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [vox-tech] update on the audio CD problem



On Fri 27 Jan 06,  3:17 PM, Bill Kendrick <nbs@sonic.net> said:
> On Fri, Jan 27, 2006 at 04:05:23PM -0500, Peter Jay Salzman wrote:
> > No.  The CPU is involved in many read-copy operations when the signal passes
> > through the sound card.
> <snip>
> 
> It was my understanding that in this "analog" CD audio playback scheme,
> the data is extracted by the CD Drive itself, converted to analog with the
> drive's own built-in DAC (just like what's in a CD Walkman or a stereo),
> and then wired directly to the sound card's "Line In" pins, and passed
> along to the speakers.  (Mixed on the card in an analog state.)
> 
> So in this case, the only time the PC's CPU is used is to tell the CD player
> "Play", then it sits idle.  Everything is done by the CDROM drive.

you're not thinking low level enough.  system calls are performed by the
kernel.  when a read() is performed, the kernel reads data from a file
abstraction of a hardware device.  the data is in kernel space.  the data
must be recopied into user space.

now the kernel must execute write().  it reads data in user space back into
kernel space to perform the write() to the sound card's file abstraction.

a kernel always executes system calls in kernel mode.

> In the "digital extraction" mode (which Norm has to do -- perhaps because
> that little wire connecting the CD drive to the soundcard is missing),
> the CPU is used to actually take the data off the CD and send it to the
> sound card (via the motherboard, rather than that little wire).

not quite.  with digital extraction, DMA transfer is used to transfer data
directly from the ATA device to userland memory.  that's the whole point of
DMA transfer.

pete
_______________________________________________
vox-tech mailing list
vox-tech@lists.lugod.org
http://lists.lugod.org/mailman/listinfo/vox-tech



LinkedIn
LUGOD Group on LinkedIn
Sign up for LUGOD event announcements
Your email address:
facebook
LUGOD Group on Facebook
'Like' LUGOD on Facebook:

Hosting provided by:
Sunset Systems
Sunset Systems offers preconfigured Linux systems, remote system administration and custom software development.

LUGOD: Linux Users' Group of Davis
PO Box 2082, Davis, CA 95617
Contact Us

LUGOD is a 501(c)7 non-profit organization
based in Davis, California
and serving the Sacramento area.
"Linux" is a trademark of Linus Torvalds.

Sponsored in part by:
O'Reilly and Associates
For numerous book donations.