Re: 10KB for the OS?
Indeed, RAM usage is a more useful metric… coding for tight flash isn't too bad, but coding for tight RAM is.
I once had to code for a TI MSP430F135 which is a 16-bit proprietary microcontroller with 16kB flash and 512 bytes of RAM. That was tough!
We found we were able to de-solder the original MCU and drop a MSP430F149 in its place, which gave me some much needed breathing room: 2kB RAM and 60kB flash. Not all designs permit this though, and most microcontrollers available to hobbyists are skint in the RAM department.
