Questions about PSIM

[CARERI/SEG]

Hi there,
	We have downloaded the C-tools for “PowerPC-rtems” for
platform Linux and cygwin.
And there are the tools: powerpc-rtems-gdb and powerpc-rtems-run(PSIM) .
But after I tried some times, I am still puzzled:
	What the PSIM can do? Can it be used with GDB to simulate the
executing of each instruction 
and to set breakpoints on the instruction? So I can debug the PowerPC
program on my Linux or 
Cygwin host.
	If it can , how to do it ? 

Any help would be thankful.

Su Wenming