[ECOS] Debugging in resource limited environment

["Robert Cragie" <rcc at jennic dot com>]

I have a system built on an OpenRISC CPU in an FPGA where the amount of
memory I have is very limited (i.e. 64K for code and data). I want to be
able to debug the application but cannot afford to have Redboot running
separately and downloading on top of it, so I want to be able to combine the
GDB stubs in with the application. Downloading isn't an issue as the RAM is
dual-ported and can be written to by the host PC in which the target board
sits.

Some questions which therefore spring to mind are:

1) How should I configure the target application? At the moment I'm doing a
RAM build and adding in GDB stubs, but saying that I am neither a ROM
monitor, nor do I want to run with a ROM monitor. Is this OK?

2) The application as configured above runs fine and drops into
cyg_user_start() OK, and I see a '+' coming out from the serial port. But
how to then debug it - are the debug serial ports interrupt driven, i.e.
should it just work?

3) How do I 'attach' to the already running application and stop it somehow
so I can single step/ set breakpoints etc.?

4) What do I have to do to GDB to stop it downloading?

I kind of feel I'm on the right track and have debugged RAM builds
downloading and debugging via a JTAG ICE before but not using built-in GDB
stubs in an environment where the code is already effectively downloaded, so
I was wondering if I'm on the right track.

Any help appreciated.

Robert Cragie, Design Engineer
_______________________________________________________________
Jennic Ltd, Furnival Street, Sheffield, S1 4QT,  UK
http://www.jennic.com  Tel: +44 (0) 114 281 2655
_______________________________________________________________


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