How to drop into UBoot command line from linux?

Hi all,
I was wondering if there is any way, while connected to serial console, for example on a Dockstar or a Zyxel NSA320/325, to leave the linux command line and drop to UBoot command line.
On other machines with different bootloader, like OpenBoot, it is possible to use an escape sequence from the keyboard on the serial console, to drop to the boot loader and issue commands.
That would be quite useful if kernel hangs or the device becomes really slow and a remote reset would be uselful to restart the device.
Of course the serial connection has to be forwarded over ethernet in some ways, like a concentrator.
Any idea for such an escape sequence?
Thanx in advance.
Paolo

Paolo,

It is not possible to run u-boot in Linux. Once u-boot starts the LInux kernel, it is no longer running, it exits completely and is no longer in memory.

-bodhi
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Hi bodhi,
thanx for your reply.
After asking I realized myself the other devices I mentioned, where it is possible to drop into the bootloader from the OS command line, actually have a separate LOM (Lights Out Management) CPU that starts and keeps running the bootloader as soon as the power supply is active, regardless of the CPU the OS use and is booted upon.
Such an example are SUN servers or HP UX servers: machines actually far different and far more expensive than a simple Dockstar or Zyxel NAS.
Paolo.