Computers as Components, 2nd Edition

204 CHAPTER 4 Bus-Based Computer Systems

for this code that generates button depressions to exercise the state machine. We

will also need to simulate the advancement of the system clock. Trying to directly

execute the interrupt handler to control the clock is probably a bad idea—not only

would that require some type of emulation of interrupts, but it would require us to

count interrupts second by second. A better testing strategy is to add testing code

that updates the clock, perhaps once per four iterations of the foreground while

loop.

The timer will probably be a stock component, so we would then focus on

implementing logic to interface to the buttons, ...