Petzold's "Code" starts at pretty much nothing and ends up with a programmable computer made using transistors. It's far more primitive than what you want to en

Petzold's "Code" starts at pretty much nothing and ends up with a programmable computer made using transistors. It's far more primitive than what you want to end up with (that is, you intend to start with an OTS microprocessor and build around that) but it's certainly useful knowledge.