Bugs

With all these successful screenshots, you might think this stuff just turns out correctly on the first try... here is a good example of how tricky it is to get everything right:

I am trying to print the 'H' in "Hello world". It should line up in the upper right of the black box. Instead, there are sets of white pixels spread out in the middle of the screen (look closely, they come in pairs spread apart, with one solid line - the bar of the 'H').

This tells me two things:

1. My starting point into the video memory is short by about one xterm height
2. My next row code is off, by maybe 6 or so