Some people are referring to trap instructions and others are
referring to system call instructions.  There are two different PowerPC
instructions.  One enters the OS trap handler, the other the system call
handler. 

	The trap instruction is similar to the branch instruction in that
it can trap on many different comparison results.  GDB and other programs
use specific variations of the instruction to mark breakpoints, etc.  You
might be able to encode some information that way as long as you use forms
of the instructions guaranteed to trap.

	There is no way to encode information in either the system call or
trap instruction itself to be passed to the handler.

David