Uwe. What kind of hardware tools to you have available? Do you have access to an Oscope?
Not usually, but I might be able to get access to one from time to time. What can I do/check if I have one?
You can watch the write line on the chip and see if its getting asserted. Then you know for sure if its flash chip or chipset.
Say I manage to flash targets/bitworks/ims/ims/fallback/linuxbios.rom (that's the only ims image <= 256K, so I'll have to use it as my chips are 256K, is that correct?), connect a serial cable on ttyS0 (ttyS1?),
The IMS config is setup for a 29f040b which is a 512k part. Did you change the rom size in the config file? But yes your rom size needs to match your chips.
115200 Baud, 8N1. Should I be able to get some debug output with the current code in svn?
Yes you will get some boot messages and it will try to dump the spd contents.