Answering my own question here. I thought DavyGravy had addressed how to deal with this problem of flashing with tftp via serial, and I found where he had.
First, "MANUAL Directions for Upgrading U-Boot" here:
http://forum.doozan.com/read.php?3,6965
By carefully following these steps, using the uboot for the Dockstar, I was able to reflash my uboot. I was using Ubuntu on a laptop as the tftp server, with a direct wired connection. After uboot was flashed I changed ipaddr and plugged the Dockstar into my router.
Then, how to flash with serial, "Mainline Minimalist Wheezy Installation via Debian Installer/Netboot":
http://forum.doozan.com/read.php?2,7277,7277#msg-7277
These instructions are for the Pogoplug E02. As suggested, I got uImage and uInitrd for the Dockstar from here:
http://d-i.debian.org/daily-images/armel/daily/kirkwood/netboot/marvell/sheevaplug/
I put them in my /var/lib/tftpboot directory, and then downloaded and ran them as shown in the directions. Because I am flashing a Dockstar, I had to use the proper machine id, "setenv machid bb6" (equal to 2998 decimal).
The Dockstar booted properly into the debian installation, and I was able to complete the flashing to usb in about half an hour. It boots properly now to wheezy.
Next I will flash a rescue environment.
Thanks, Davy.
Edited 1 time(s). Last edit at 11/23/2012 12:03PM by lyzby.