GNU's gdb from Cygnus Support

To use the debug Monitor with GNU's gdb, connect the serial port that gdb will use, to the Monitor's tty0 (the console) on the target board. i.e., gdb only uses one serial port.

Compile and link your modules with the -g option. This will generate the extra information that is required by gdb. For example,

	pmcc -g -o bubble bubble.c

Invoke gdb.

	% mips-lsi-elf-gdb -b 9600 bubble

where 'bubble' is the name of the object file that you are debugging. The option "-b 9600" specifies that 9600 baud will be used for the Host-to-Target communications.

By default gdb from Cygnus Support runs in a windowed mode. However, it the time of writing, the windowed mode was incomplete/buggy, so you might prefer to run it in non-windowed mode. To select non-windowed mode, add the option -nw to the command line.

	% mips-lsi-elf-gdb -nw -b 9600 bubble

gdb normally expects your monitor to have a prompt of "PMON> " (note the space). If your monitor uses a different type of prompt you can either change it in the Monitor using the set command or tell gdb what prompt to expect. For example,

	(gdb) set monitor-prompt IMON>

Note that this command does not expect quotes around the prompt, but gdb will take the entire string including trailing spaces. So be careful to type the string exactly.

Next you must specify the target type, and serial port that will be used to communicated with the target. For example,

	(gdb) target lsi /dev/ttyb

this specifies that the target is running LSI Logic's PMON (or IMON), and that the target is connected to /dev/ttyb on the host. If you are using MSDOS you will need to specify one of the COM ports. eg. com1.

To download your program to the Target issue the "load" command. No arguments are necessary as gdb has all the other information it needs.

	(gdb) load

If you simply want to run your program, you can just type "run". But if as is more likely you want to be able to set breakpoints and single-step your program, you should type,

	(gdb) b main
	(gdb) run

this will set a breakpoint at "main" and execute the program until it reaches that point.

The following table is a summary of the most frequently used commands:

Brief Command Summary
gdb	PMON/IMON equivalent	Description
step	t	Single Step
next	to	Step Over
b addr	b addr	Set Breakpoint
delete	db *	Delete
c	c	Continue
run	g	Start Execution

When debugging the Host-to-Target communications it is sometimes useful to create of log of all the transactions. The following command writes a log to the file "remote.log".

	(gdb) set remotelogfile remote.log

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