🚀 go-pugleaf

F line emulation is a technique which allows instruction set extension
on the 68xxx family.  An F-line exception occurs when an instruction
with the first nybble of the opcode is F (1111 binary).  The exception
handler is entered, which may then examine the rest of the instruction
and emulate just about anything you'd like.  Getting an F-line
exception in normal code is usually the result of jumping to a word
which isn't actually an instruction boundary.  It may also be caused
by faulty memory, which returns Fxxx instead of the correct value.
Additionally, the FPU opcodes reside in the Fline space, so if you
have inline FPU operations, they will trap, allowing software
emulation.

Hope that helps.

Mark Huth