about remote debug using debug monitor

[zhao mindong]

"GDB also can mimic a human user and use a ROM monitors normal debug 
commands as a backend. This consists mostly of sending and parsing ASCII 
strings. All the ROM monitor interfaces share a common set of routines in 
gdb/monitor.c."
i have saw some article said so,but i do not know how does the gdb 
communicate with the ROM monitor(such as
Motorola's picobug monitor).For example i want to send a "step" command to 
the picobug monitor,in which source file does the gdb finish the work of 
encapsulating the "s" instruction to be a format data packet like 
"$s..#checksum"?If the gdb use the style of ROM monitor,does it still use 
the gdb remote serial protocol which implemented in remote.c?
OK,another question,does anybody know in which source file does gdb finish 
writing a ascii string to the serial port COM1?I ever add some code in the 
function dos-write(....char * str ...) in ser-go32.c to get the str(i think 
it is the thing that gdb writes to the COM1),but after i compling the gdb 
and running,i get nothing..
is there anybody have done such work?now the only thing i can do is to be 
drown in the sea of gdb source code.help me....


_________________________________________________________________
MSN 8 helps eliminate e-mail viruses. Get 2 months FREE*. 
http://join.msn.com/?page=features/virus