Debugging

chapter

5

Quit Thinking and Look

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.”

—SHERLOCK HOLMES, A SCANDAL IN BOHEMIA

War Story. Our company built a circuit board that plugged into a personal computer and included its own slave microprocessor, with its own memory (see Figure 5-1). Before the host (main) computer could start up the slave microprocessor, it had to download the slave’s program memory; this was accomplished with a special mechanism in the slave, which allowed data to be sent from the host through the slave to the memory. When this was done, the slave would check for errors in the contents of the memory (using a magical thing ...