1. I generally try to use the serial port as my
debugging tool, since the company that I work for
is unwilling to buy emulators. I use some software
routines that convert a hex byte to two ascii
numbers and then send that out through the serial
port.

2. Use a digital storage oscilloscope(DSO) to look at
various lines (this is especially helpful when
writing drivers for SPI and I2C devices). Also
the DSO is useful when adding external memory
and devices which use external memory space.
You can see if the ALE,RD,WR, and CS lines have
the proper timing relationships. Also you can see
any hardware errors such as shorted data lines,
address line, etc. The DSO can be used as a poor
man's logic analyzer.

3. Using these two tools, your brain and
troubleshooting techniques, I can generally
solve 99.9% of the problems.

4. For the 0.1% problems that I can't solve, I use
a monitor program from Keil.

5. I design testability in from the beginning.
The methods usually vary from design to design.
I usually design in commands that can be accessed
through the serial port, that allow me access
(read/write)to various devices in the design.
This allows me to test boundary conditions, etc.
and allows me to automatically log the data for
each test.

Jacob