I've never hacked assembly on an AVR, but I have on the MSP430, and it's a really elegant architecture to work on; expressive enough to let you get stuff done w

I've never hacked assembly on an AVR, but I have on the MSP430, and it's a really elegant architecture to work on; expressive enough to let you get stuff done without hurling your development board at the wall, but constrained enough to make figuring out a neat optimisation both satisfying and useful. Also, the MSP430X has 20-bit registers, just for that added level of surreality. However, even I have limits: stay clear of PIC12. It's just... bizarre, and not in a good way. (Somewhere I have 2/3 of an 8080 emulator for the MSP430, written in machine code. It ran on the basic Launchpad, with 2kB of RAM, and booted CP/M using an SD card for storage and an external serial SRAM device for memory swap. Sadly, while I got it talking to an AT keyboard, I never got a screen to work, and I've since broken up the hardware for other projects. The emulator core was 1kloc of assembly. The 8080 is surprisingly orthogonal.)