Net-booting a linux kernel on an Ultra 5

[Jim MacBaine <jmacbaine@gmail.com>]

Hello,

I'm trying to make a Sarge system run on an Ultra 5 workstation,
booting from net with root on nfs.  This is what I managed to do
already:

- compiled a sparc64 cross compiler on a x86 system
- cross-compiled kernel 2.6.12 for sparc64
- ran "elftoaout" on the kernel
- set up rarp and tftp server on the server
- debootstrapped and exported a sparc sarge system on the server

I got the Ultra 5 so far to load the kernel via tftp and boot it. But
now I'm stuck at a problem, I seem unable to solve. The kernel mounts
the nfs root but then complains that it is unable to open an initial
console:

[...]
input: Sun Type 5 keyboard on su/serio1
input: Sun Mouse on su/serio0
IP-Config: Guessing netmask 255.255.255.0
IP-Config: Complete:
      device=eth0, addr=192.168.17.15, mask=255.255.255.0, gw=255.255.255.255,
     host=192.168.17.15, domain=, nis-domain=(none),
     bootserver=192.168.17.1, rootserver=192.168.17.1, rootpath=
Looking up port of RPC 100003/2 on 192.168.17.1
Looking up port of RPC 100005/1 on 192.168.17.1
VFS: Mounted root (nfs filesystem) readonly.
Warning: unable to open an initial console.
eth0: Link is up using internal transceiver at 100Mb/s, Full Duplex.

Am I missing a kernel config option? I built the kernel with the
OpenBoot PROM console and the framebuffer console compiled in.

Or am I missing a boot parameter? My kernel command line currently
looks like this:

ok printenv boot-file
boot-file = 192.168.17.1:/tftpboot/sunny.aout root=/dev/nfs
nfsroot=192.168.17.1:/vol/nfsroot/sunny ip=rarp

Thanks in advance, 
Jim