SCSI emulation
==============

PUAE's SCSI emulation allows any CD-ROM drives on the host machine to be
used as Amiga SCSI devices within the emulation. You can use this to fully
support CD-ROMs, audio discs, CD-writing, etc. in AmigaOS. SCSI emulation is
also required to emulate a CD-TV or CD32.

In general, to enable SCSI emulation simply add the 'scsi=true' option to
your config file. Any useable CD or DVD devices that PUAE finds will be
available to AmigaOS via the device driver 'uaescsi.device' on consecutive
unit numbers starting at unit 0. However, depending on your host platform,
there may a number of host configuration issues which can make using the
SCSI emulation problematic.

I'll start with the easy stuff. If you're running PUAE on AmigaOS (or a
clone) or BeOS, then don't worry. The SCSI emulation works transparently.
Just set the 'scsi=true' config option and away you go.


Linux
-----

Starting with version 0.8.29, UAE's SCSI emulation can directly
communicate with the Linux kernel's CD-ROM driver to access a single
CD/DVD drive (it currently doesn't support multiple drives, unlike the
libscg back-end).

To use, simply specify the drive's device file with the configuration
option 'scsi_device=' (as well as, obviously, 'scsi=true'. For example:

scsi_device=/dev/hdc

You should ensure that the account you use to run PUAE has permission
to access this device file.

You may run into problems if your Linux distribution has the HAL
daemon installed. This software continually polls your removable media
drives to detect insertion/removal of discs, and this activity may
interfere with PUAE's SCSI emulation. A solution to this problem
needs to be investigated.

This Linux-native SCSI back-end is less well-tested than the libscg
back-end. It has not been tested with real SCSI devices (only ATAPI
devices) and depending on the bugginess of your Linux ATAPI driver
and/or the firmware of your drive, problems may occur.


Linux and libscg
----------------

Using the libscg-based SCSI emulation on Linux can be troublesome,
depending on how your Linux system is set up. If cdrecord works on
your set-up, then there's a good chance that the SCSI emulation will
too since it uses cdrecord's SCSI transport layer, libscg. There are
some points to be aware of, however.

Firstly, you need a kernel module installed which support sending SCSI
commands to your CD/DVD device. For real SCSI devices, this will be the sg
(SCSI generic) module. For ATAPI devices on 2.4 kernels, you need the
ide-scsi (SCSI over ATA) module and the sg module. (On 2.6 kernels, the
ide-cd driver directly supports sending SCSI commands to ATAPI devices, but
we'll come to that in a minute.)

If you're using sg or ide-scsi and sg, then your devices are accessed via
device nodes of the form /dev/sg0, /dev/sg1, etc. You need read and write
permission on all of these for SCSI emulation in PUAE to work (Note that
cdrecord is typically installed SUID root, so typically the default
permissions on the /dev/sgx nodes will not be sufficient. Installing PUAE as
SUID root is one possibility, but not a terribly good idea security-wise.
One solution to this is to set the owner of the /dev/sgx nodes as the group
'cdrom' and add you own user account to that group. For example, as root, do

# chgrp cdrom /dev/sg*
# adduser gnostic cdrom

Use your own account ID, of course, rather than 'gnostic', which is me.

If your system doesn't have the adduser command, you can always manually
edit the /etc/group file or use some whizz-bang, GUI-based user/group
configuration utility to do the job.

If you log in as yourself again and start PUAE (remember to add 'scsi=true'
to your config file first), then the SCSI emulation should work. If so you'll
see something like this logged to the console when PUAE starts up.

scsibus0:
  0,0,0  0 'BTC     ' 'BCE1610IM       ' 'A.20' CD-ROM
  0,1,0  1 *
  0,2,0  2 *
  0,3,0  3 *
  0,4,0  4 *
  0,5,0  5 *
  0,6,0  6 *
  0,7,0  7 *
SCSIDEV: 1 devices found
support_scsi = 1 support_ioctl = 0

If you're using a 2.6 kernel, PUAE can access ATAPI devices on the host
directly via the kernel ide-cd driver without the sg kernel module. To do
this on older 2.6 kernels, add the config option

scsi_device=ATAPI

in your config file (remember to add scsi=true also) and make sure you have
read and write access to the necessary device nodes corresponding to the
devices you wish to use with UAE (for example, /dev/hdc or whatever).

For newer 2.6 kernels (>=2.6.12?), the libscg ATAPI transport method no
longer works and you have to use the ATA method. To do this, specify the
device path to your CD/DVD drive with the scsi_device= option. For example:

scsi_device=/dev/hdc


MacOS X
-------

Now we get to the real problems. SCSI emulation with PUAE on OS X is
currently a real pig, due to some features and limitations of OS X. The big
problem is that you need a writable device - a CD or DVD burner - for SCSI
emulation to work at all. This is because the OS X kernel will only let you
send SCSI commands to a writable device (for this problem to be solved, UAE
would need to support a real SCSI emulation - the current implementation is
simply a wrapper around a host SCSI device).

The second problem is that the Finder does not like sharing a removable
media device with any other application. For SCSI emulation to work, you
must start UAE without a disc inserted in your CD or DVD writer. Otherwise,
Finder will auto-mount the disc and not let UAE access the device. A
different (more drastic) solution is to kill OS X's auto-mount daemon, but the
procedure for doing this differs depending on which version of OS X you
have. Somebody remind me to look this up and fill in the details here.

The third problem is getting UAE to locate your CD or DVD writer. libscg on
OS X (the SCSI transport layer which UAE uses) doesn't support bus-scanning
on OS X. Only one device can currently be used with UAE, and you have to
name it explicitly with the 'scsi_device=' option in your config file.

For the first CD writer, this will be:

scsi_device=IOCompactDiscServices/0

For the first DVD writer, this will be

scsi_device=IODVDServices/0

Also remember to add the 'scsi=true' option to your config.

If set up correctly, UAE will output something similar to the following when
starting up:

scsibus:0
  0,0,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,1,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,2,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,3,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,4,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,5,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,6,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,7,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,8,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,9,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,10,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,11,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,12,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,13,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,14,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
  0,15,0  0 'YAMAHA  ' 'CRW842S         ' '1.0f' CD-ROM
SCSIDEV: 16 devices found
support_scsi = 1 support_ioctl = 0

and then it'll complain a bit about being unable to get exclusive access and
then it'll say

(0,0,0) = uaescsi.device:0

Okay. Don't look so worried. What's happening here is that UAE is trying to
scan for SCSI devices, can't, and ends up finding the same device 16 times.
Not very elegant, I know, but it works. I will tidy this up eventually. If
Finder has an exclusive lock on your device because it has mounted a disc,
UAE will just say 'Unable to get exclusive access to device' once and say:

SCSIDEV: 0 devices found
