>/ This might be a silly question, but i was wondering what exactly the role of
/>/ OpenOCD is in debugging. I mean the internal functioning. I am assuming it
/>/ acts like a mediator and just enables debugging on a remote device. But i am
/>/ still not clear how this is done. Can anyone shed some light on this please
?
/>/ Ex When a break point is set at the gdb, does OpenOCD store this somewhere
and
/>/ check if the particular symbol has been reached on the remote device or does
/>/ it do something a lot simpler like, tells gdb which instruction is running
and
/>/ let gdb decide if the instruction is of interest.
/>/
/>/
/OpenOCD controls and manages the hardware debug interface to a target.
Traditionally, the interface is JTAG, though support is being added for new
interfaces like SWD (serial wire debug). Gdb has no knowledge of the specifics
of the remote target. OpenOCD functions as a gdb server, receiving and acting
on higher level user commands (e.g., breakpoint), and alerting gdb to the
occurrence of events (e.g., halting).
Using breakpoints as an example... both gdb and OpenOCD store and manage
breakpoints. But OpenOCD does what is necessary to ensure that the target halts
when execution reaches the breakpoint. The details are target specific, but
generally speaking, breakpoints can be classified as either "hardware" or
"software". For software breakpoints, the instruction at the breakpoint address
is subsituted with the target processor breakpoint instruction. Hardware
breakpoints use a mechanism provided by the debug hardware on the target
processor, if any, to the same end. Hardware breakpoints are handy in cases
where the code can not be patched with the breakpoint instruction, such as when
the code is running out of ROM, or has not yet been loaded into memory.
Note that OpenOCD can be used stand-alone; i.e., without gdb, though its telnet
port. This is handly for low-level debugging.
In stand-alone OpenOCD can be used for Flash programming too, by simple
script or a sequence of commands passing as -c command arguments when
launching OpenOCD.
Hope this helps,
Mike
Laurent Gauch
http://www.amontec.com
Amontec USB JTAGkey Series
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