I agree with you, Jon. There is a place for emulators and a place for simulators. Probably in excess of 90% of any given firmware I develop is logic while 10% or less is the actual I/O with external devices.

I've developed the code for quite a few designs far before they had the hardware ready. When they finally got the hardware ready I already knew 90% of my code was done, tested, and working so that when they had the hardware ready I only had to write and test the remaining 10% of the code--the code that interacted with the hardware. Each time they were surprised how quickly I gave them finished code after receiving the final hardware design.

Simulators are also nice when you are traveling. I've done development and testing with a simulator while on a plane and in a hotel. An emulator in a hotel might not be a big deal (though it's one more thing to carry around), but it'd be a hassle on a plane.

I feel it's just a matter of knowing the limits of your simulator and realizing that there are certain things that might work on your simulator that won't work on the real hardware. But, in my experience, 10% or less of my code is hardware-dependent. The rest is logic-based and can be thoroughly tested with confidence within a simulator.

Regards,
Craig Steiner