It compiled under CygWin and I found the part where it breaks (it begins with erasepage not geting 'e' command echoed). Can I use it to upload boot images, do I use files output by your editor, and what is proper address for MkII? (Sorry, all this is certainly written somewhere, but it's past 2 AM...)

Update: OK, found that I can and address is a000. The readbyte after 'e' command returns 0x0a (line feed), instead of echoed 'e'. So much for tonight...