Re: Obtaining an IOSCSIMultimediaCommandsDevice instance

Hi again Chris,

OS X does not support sending read/write commands except via the BSD

layer (read/write/pread/pwrite/ioctl). Do you suspect that the drive

is not accessing the media during a particular test you are running

and therefore must use FUA?

I am in the process of creating an error correcting CD audio extractor for

OS X.  Part of the error-correcting algorithm is to read the same sector

directly from the media several times and then compare the results.  If

the reads match, it is assumed to be good; if they don't, the drive speed

is slowed, the sector is re-read and compared again, etc.  Obviously if I

read the sector once from disc and then the subsequent reads return

identical data because of the drive's cache the scheme will fail. 

Unfortunately, this is exactly what happens using the DKIOCCDREAD ioctl. 

Hence the need to use FUA!

I am aware of "hackish" ways around this such as reading data blocks

larger than the drive's cache, but this is just that- a hack when nothing

better is available.  Plus, some drives have large caches!

Stephen

-- Chris

On Jan 24, 2006, at 4:45 PM, email@hidden wrote:

Chris,

I am familiar with the ioctls in IOCDMediaBSDClient (READ, READ

TOC, etc).

I would like to use (primarily) the READ (10 or 12) command.  I

need to

set the FUA bit- I don't believe this is possible with the DKIOCCDREAD

ioctl.

Stephen --

What type of raw commands are you trying to send? Have you looked at

the list of CD ioctls OS X supports?

-- Chris

On Jan 24, 2006, at 3:46 PM, email@hidden wrote:

Hi Chris,

Thanks for the response!

You might want to start out with what you are trying to achieve.

Are

you trying to send commands from kernel-level code or user-level

code?

Preferably user-level.

If the latter, you might want to check out the sample code found

in /

Developer/Examples/IOKit/scsi/SCSITaskLib and consult Accessing

Hardware From Applications (http://developer.apple.com/

documentation/

DeviceDrivers/Conceptual/AccessingHardware/AH_Intro/

chapter_1_section_1.html).

I've read these now (thanks for the pointer), and also consulted the

example code, but I'm still confused.  The problem for me is that

this all

seems geared towards CD/DVD authoring and authoring-capable

devices.  For

my application authoring doesn't matter.  All I "need" to do is

send a

small subset of the MMC-2 commands to the drive to access an audio

CD.  I

have had some success creating an MMCDeviceInterface, but that

really

doesn't help me because I can't obtain exclusive access from

SCSITaskDeviceInterface.  Even if I could, I'm not sure how that

would

help me because I really don't want to send raw SCSI tasks.  I

still don't

understand enough about IOServiceGetMatchingServices to know which

key to

pass in to try and get an IOSCSIMultimediaCommandsDevice.

Stephen

HTH,

-- Chris

On Jan 24, 2006, at 2:30 PM, email@hidden wrote:

I will start by saying the IOKit is pretty much a black box for

me.  I've

done only basic tasks such as creating a dictionary and calling

IOServiceGetMatchingServices for it.  Unless I've missed

something,

the

IOKit documentation is slightly less than stunning so I'm asking

for help

here.

I want to create an IOSCSIMultimediaCommandsDevice for

accessing an

audio

CD using MMC-2 commands.

If I may rant for a moment, the superclass to

IOSCSIMultimediaCommandsDevice is IOSCSIPrimaryCommandsDevice

defined in

"IOSCSIPrimaryCommandsDevice.h".  I don't even have that header

file in my

10.4u SDK!  It's only in the 10.3.9 IOKit.  To boot, that class'

superclass is IOSCSIProtocolInterface which also appears only to

exist in

my 10.3.9 SDK.

Anyway, IOSCSIMultimediaCommandsDevice is a subclass of IOService.

Can

anyone step me through how I would go about obtaining an instance

of this

class?

Thanks!

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