What are the advantages of using FPGAs over TTL in intro computer architecture?
Given the goals of the class, I think the TTL approach is fine, and I say this as an "FPGA guy". FPGAs are a sea of logic and you can do all sorts of fun stuff with them, but there's only so much that's humanly possible to do in a semester.
Looking at your syllabus, your class is a mix of the logic design and "machine structures" courses I took in undergrad. (Plus, it's for CS majors. I'm all for CS majors having to face real hardware--letting them get away with writing code seems like a step back.) At this introductory level, where you're going over how assembly instructions are broken down, I see no real benefit to having students do things in code versus by hand. Doing HDL means learning the HDL, learning how to write synthesizable HDL, and learning the IDE. This is a lot more conceptual complexity and re-abstraction. Plus you have to deal with software issues.
Generally the point of a course that uses FPGAs is to practice creating logic that is useful--useful for talking to peripherals, serial comms, RAM, video generators, etc. This is valuable knowledge to have, but it seems very much out of the scope of your course. More advanced classes in computer architecture have students implement sophisticated CPUs in FPGAs, but again, this seems out of the scope of your course.
I would at the very least devote a lecture to FPGAs. Run through a few demos with a dev board and show them the workflow. Since you're at Mills, perhaps you could contact the folks at Berkeley who run CS150/152 and go see how they do things.
One benefit of using TTL though would be that for the very elementary circuits, the details of the HDL would sort of mask the actual circuitry, and most students would simply spend most of the time writing and learning HDL. I think TTL's for the first part and then FPGA for the architecture part would be better, since it's hard to actually make a programmable system with TTLs.
I very much agree with Photon. There are many advantages to using FPGAs. Here are a few interesting points to consider:
1) Easy platform for trying out a gate design very quickly, without hours or potentially days of work wiring things up. FPGAs allow potentially very complex digital designs quite easily. (MUCH more theory, less busywork)
2) Significant portions of a student's work could be done in simulation outside of the lab.
3) The software environment is free (generally including the simulator).
4) There are many relatively cheap FPGA platforms around. Academic pricing should help. Something like the Terasic DE0-Nano is $59 for a complete kit (and it looks pretty good). $50-60 looks to be the per-board range you'd be looking at.
5) There's a lot of really cool stuff to do with FPGAs. There are sites like OpenCores that provide hundreds of prebuilt modules for use with FPGAs. There's FPGA4Fun, which has a lot of tutorials and projects. For pure entertainment, FPGA Arcade is dedicated to building games with FPGAs. Depending on what you set up around the FPGA boards, this could make for a really fun class.
6) Some boards have digital design classes apparently ready-made for them: Intro to Digital Design (warning: large download) using a slightly old Xilinx Spartan 3E-based board. (Although that one's based on ActiveHDL, I'd personally prefer a more standard VHDL or Verilog) The major FPGA vendors also have university programs: Xilinx University Program, Altera University Program, Lattice University Program.
7) The workflow is much closer to how professional design work happens these days. Working knowledge in FPGA development is an immediately marketable skill.