ADDITIONAL NOTES:

These notes are intended to give some hints on how to work with Gem5 and where to start,
when you want to add a new board to Gem5 and support it in Barrelfish.


1. Adding a new (ARM) development board to Gem5

The place to add a new development board is in gem5/src/dev/arch/arm/Realview.py. There are
already a bunch of boards there which should get you started. If your intended board has devices
which are not yet implemented in Gem5 you can either try to use an existing one (eg another UART
device) or you have to implement it yourself. You can look at the other files in this directory
to get an idea on how to do it.

You also need to change barrelfish/tools/arm_gem5/gem5script.py to select your new device.
Watch for the 'machine type configuration' and change it to

system.realview = Your_Board_Class()

In the Barrelfish code itself you probably have to adjust the hardcoded device addresses in
'kernel/arch/arm_gem5/integrator.c'. If you added new devices you'd also need to write a device
driver and make according changes to the code.

This should get you started. If you have any problems which are beyond the scope of these notes,
then ask on the Gem5 and/or the Barrelfish mailing list for help.


2. Working with Gem5

2.1 Debugging Barrelfish on Gem5

Gem5 has nice remote debugging support but needs some configuration in order to work. There is
already a GDB script in tools/arm_gem5/debug.gem5.gdb which does the work for you. In order to
attach the remote debugger to Gem5 just change to your Barrelfish build directory and run

'arm-linux-gnueabi-gdb -x ../tools/arm_gem5/debug.gem5.gdb'

and Gem5 will break in whatever code currently executing in the simulator.
If you want to start debugging from the first line of code on you have to modify 
'gem5/src/sim/system.cc'. Look for this line

int rgdb_wait = -1;

change it to

int rgdb_wait = 0;

and recompile Gem5. That way Gem5 will wait for a remote debugger to attach before executing any
simulated code.


2.2 Debugging Gem5

In order to debug Gem5 you want to build the debug binary 'gem5.debug'. Then just open this binary
in GDB and you can step the Gem5 code. 

For more information about Gem5's debugging functionality visit http://www.gem5.org/Debugging.

TO BE EXPANDED...