If the board is PCI based you should be able to get the physical address of the rom via the PCI register and/or pci_device_attach. If it’s ISA, the address is most probably control via switched or hardwired.
Once you get the address you must map it with map_device_memory to get access to it.
I am currently working on VP5, 6U VME bus Embedded Computer. I have a 8MB onboard Flash memory mounted on to the board, how to identify weather it is PCI or not.
Can you provide me the system call details which you have provided me (pci_attach_device and map_device_memory)
It there is any sample code for reading data on the onboard flash, can you please provide me any source code.