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system from scratch, you should seriously consider having a BDM or JTAG interface available
for developers so that they can attach a BDM or JTAG debugger, even though it may be
expensive. Most commercial embedded boards are already equipped with the appropriate
connectors.
There is at least one open source BDM debugger available complete with gdb patches and
hardware schematics. The project is called BDM4GDB and its web site is located at http://
bdm4gdb.sourceforge.net/. This project supports only the MPC 860, 850, and 823 PowerPC
processors, however. Though this is quite a feat in itself, BDM4GDB is not a universal BDM
debugger.
The LART project (http://www.lart.tudelft.nl/) provides a JTAG dongle for programming the
flash of its StrongARM-based system. This dongle's schematics and the required software are
available from http://www.lart.tudelft.nl/projects/jtag/. Though this dongle can be used to
reprogram the flash device, it cannot be used to debug the system. For that, you still need a
real JTAG debugger.
If you are not familiar with the subject of debugging embedded systems with hardware tools, I
encourage you to look at Arnold Berger's Embedded Systems Design (CMP Books), and Jack
Ganssle's The Art of Designing Embedded Systems (Newnes). If you are actively involved in
designing or changing your target's hardware, you are likely to be interested by John Catsoulis'
Designing Embedded Hardware (O'Reilly).