Problem booting from USB floppy

[Edgar Denny <e.denny@ic.ac.uk>]

Hi all,

I'm having problems booting from a USB floppy.

My BIOS supports USB floppy boot (thinkpad X20), so I can boot a kernel 
from floppy no problem. 

Since the USB storage devices work using some sort of SCSI emulation,
I have replaced the original kernel image on my boot disk with one
that has SCSI support and USB mass storage support built in.

In addition, I've used knl to modify the kernel with the following
options:

knl --kernel=/floppy/linux --prompt --root=/dev/sda

In the syslinux.cfg file that accompanies the kernel in my
initial debian boot disk, I have the following default:
the following:

DEFAULT linux
    APPEND vga=normal noinitrd load_ramdisk=1 prompt_ramdisk=1 
    ramdisk_size=16384 root=/dev/fd0 disksize=1.44

Since the usb floppy is on /dev/sda, I have added the following lines to
the list of boot labels:

LABEL usb
    KERNEL linux
    APPEND vga=normal noinitrd load_ramdisk=1 prompt_ramdisk=1 
    ramdisk_size=16384 root=/dev/sda

My problems start when I try to load the second root 
floppy disk into RAM disk. 

I get the following odd behaviour:

(1) If I boot the kernel with the default "linux" label, then as
    soon as the non-USB floppy driver is loaded into the kernel, then
    the kernel prompts for the ramdisk. I get the following:

    VFS: Insert root floppy disk to be loaded into RAM disk and press
    ENTER.

    As expected, if I switch the floppy to the root disk and press
    ENTER, the disk fails to loaded, since the regular floppy driver
    won't work.

    Note, after the root disk fails to be detected, more of the kernel 
    loads, and I get get the following kernel messages, which suggest 
    I've biult the kernel OK:

    scsi1: SCSI emulation for USB Mass Storage devices
      Vendor: TEAC   Model: FD-05PUB   Rev: 1026
      Type:   Direct-Access            ANSI SCSI revision: 02
    Attached scsi removable disk sda at scsi, channel 0, id 0, lin 0
    sda : READ CAPACITY failed.
    sda : status = 1, message = 00, host = 0, driver = 08
    sda : extended sense code = 2
    sda : block size assumed to be 512 bytes, disk size 1GB.
      sda: I/O error: dev 08:00, sector 0
      unable to read partition table

(2) I've included (1) above since if I now boot the kernel with
    the "usb" label, which I expected to be OK, then I get no prompt 
    for the root floppy to be loaded into the RAM disk!

    Instead, I get no prompt to swap disks, I just get

    VFS: Cannot open root device "sda" or 08:00
    Please append a correct "root=" boot option
    Kernel panic: VFS: Unamble to mount root fs on 08:00

So what am I doing wrong? Why am I getting no prompt so I can take out
the boot disk, replace it with the root disk, and type ENTER to
continue with the installation?

Any help would be greatly appreciated.

Thanks,

Edgar.