Calling AVR a "joy to use" is pushing it a little far. There are things to like about AVR chips as a package, but the AVR instruction set is pretty janky. I don't understand why they're so popular compared to the MSP430.
I found the AVR instruction set pretty straight forward. Granted, it was my first forray into assembly and I learned it around 17 years ago at age 14. Maybe everything seems easy in hindsight at that age.
I've never programmed MSP430s in assembly, but I have for PICs and found their instruction set to be more funky than AVR.
So first a couple caveats: (1) I'm sure AVR is a hell of a let better than PIC, (2) I come at this from a really weird place (exclusively emulators and compilers), and (3) I'm not talking about the AVR parts themselves, which might be more cost-effective for a given project.
That said:
* Harvard architecture (split I & D memory)
* 8 bit registers
* Not at all orthogonal, and particularly painful for pointer addressing
* The stack pointer is annoying to work with
* Address wrap at physical memory bounds, rather than the bounds of address space
I could pick a bunch more nits that would only really be relevant to someone writing an emulator (complicated instruction decode, IO addressing, &c) but those are my big complaints.
Those are all true (though that an 8-bit microcontroller has 8-bit registers is… unsurprising). However I am referring to the instructions themselves, which were well-engineered to match the needs of a compiler. The result is very compact assembly for most C programs that you would write on an 8-bit microcontroller (including things like 16-bit arithmetic).
