Tried the USB Smart Cable and it failed even though Linux can see it OK. Seems there is a problem with the USB cable and the Serial smart cable will work if a USB to Serial converter is used. See:

www.frihost.com/forums/vt-100722.html

The only reliable option seems to be an Ethernet smart cable .

I did some searching on the web for Linux tools and found this:

http://z8encore.sourceforge.net/

The description of the tools (copied from the site) are:

ez8mon
This is a command-line debugger that is used during code development. This tool can download code to the device, set breakpoints, single step code, view memory, alter memory, disassemble code, and other tasks commonly found in debuggers.
flashutil
A command-line utility to program code into the flash of a device. This program has a multi-pass mode which allows several devices to be programmed consecutively with little intervention. This tool could be used on a production assembly-line.
crcgen
A command-line utility to calculate the CRC-CCITT checksum of data in an intel hexfile. This can be used to compare against the hardware CRC checksum returned by the on-chip debugger.

They are designed for the Serial and Ethernet smart cables. I managed to get these to compile under Ubuntu 8.04 after downloading specified libraries and tweaking of one file, however, on running, I was unable to connect to the Serial smart cable. I tried both serial ports on my machine and neither worked so I'm not sure what the problem is though I don't think it is the software as the serial ports work under Windows.

Running ZDS under Linux and Wine, I've only had success using the ethernet smart cable. Gave up trying to get serial cable to work; other more important things to debug than that.

There is also the device driver library at ddrz8e.sourceforge.net.