Xmodem is the right thing for an embedded target for bringup, but zmodem was tons better for BBS'ing. It performed much better than xmodem. Auto-start in zmodem is wonderful. Multi-file transfers are easy and it even sends the filenames. (My old libraries of BBS downloads, pre-zmodem, are a mess of crappy filenames.)
I guess it depends how "embedded" the target is, I guess. I'd rather write an xmodem implementation in assembler than I would zmodem. I'm envisioning that you're using xmodem to transfer "brain-stem" type firmware where you're talking to a very constrained system. (I know I've sent firmware to Ethernet switch bootloaders via xmodem over serial. Presumably I was very, very close to the metal in that case.)
Exactly. I built my first 8-bit computer after watching Ben Eater's 6502 series and the first thing I did after "Hello! World" was look up what bare minimum serial transfer I could implement that would yell if I fucked up the code in some obvious way (cant check if the data is right on the other end if the RAM is volatile and the transfer code itself is unproven). XModem fit the bill (entire spec on Wikipedia and dumb enough that an assembler beginner can do it).
cat works great over a reliable connection as long as you can get it to start and end in the right places. When the connection is reliable, the only thing that needs doing is delimiting the transfer and possibly sending metadata.
