[gentoo-embedded] USB Boot Problem

["Relson, David" <david.relson@orion-sys.com>]

G'day,

I've got a USB boot problem.

My target hardware is a PC/104 card with a Vortex86sx processor and a
128MB DOM (disk-on-module) for mass storage.  

Currently the test version of the card has a 1GB DOM which is
partitioned as follows:

       Device Boot      Start         End      Blocks  Id System
    /dev/hda1   *           1         141      142096+  6 FAT16
    /dev/hda2             142         991      856800  83 Linux

The BIOS boots to the FAT16 partition where ldlinux.sys takes over and
starts linux and all is fine.  

When I insert my USB flash drive, it is recognized as:

    usb 1-1.2: new high speed USB device using ehci_hcd and address 3
    usb 1-1.2: configuration #1 chosen from 1 choice
    scsi0 : SCSI emulation for USB Mass Storage devices
    usb-storage: device found at 3
    usb-storage: waiting for device to settle before scanning

    scsi 0:0:0:0: Direct-Access   SanDisk  Cruzer Micro  0.1  PQ: 0
ANSI: 2
    sd 0:0:0:0: [sda] 2001888 512-byte hardware sectors: (1.02 GB/977
MiB)
    sd 0:0:0:0: [sda] Write Protect is off
    sd 0:0:0:0: [sda] Mode Sense: 03 00 00 00
    sd 0:0:0:0: [sda] Assuming drive cache: write through
    sd 0:0:0:0: [sda] 2001888 512-byte hardware sectors: (1.02 GB/977
MiB)
    sd 0:0:0:0: [sda] Write Protect is off
    sd 0:0:0:0: [sda] Mode Sense: 03 00 00 00
    sd 0:0:0:0: [sda] Assuming drive cache: write through
     sda: sda1
    sd 0:0:0:0: [sda] Attached SCSI removable disk
    usb-storage: device scan complete

I need to create a rescue/install USB flash drive.  

At present my test flash drive has ldlinux.sys and the same kernel used
by the device.  Booting with "linux root=/dev/hda2" works fine.  However
for rescue purposes I need "linux root=/dev/sda" (or equivalent).

When I boot with "linux root=/dev/sda1", I get the following

    VFS: Cannot open root device "sda1" or unknown-block(0,0)
    Please append a correct "root=" boot option; here are the available
partitions:
    0300      1000944 hda driver: ide-gd
      0301      142096 hda1
      0302      856800 hda2
    Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown-block(0,0)

Evidently /dev/sda1 hasn't yet mounted.  The boot process runs into the
same problem when I use /dev/sda or /dev/sda2 for "root=".

In the past I've seen similar kernel panics when the kernel lacks the
proper disk driver.  Since the system boots fine from the DOM, I believe
my kernel has all the device drivers built in (except scsi_wait_scan.ko
which is a module).

How do I fix the boot problem?  Anybody familiar with this problem and
have a recommendation or, even better, a solution? 

Regards,

David