Been a while since I updated this...
The print routines are working fine now, and I can print strings, signed or unsigned decimal or hex to the screen or a buffer. Unfortunately, I don't have format specifiers, so everything prints as %X or %d, but I can't do %8X, or even %08X

I started working on a keyboard driver, and have verified that I can read the appropriate CRU bits. Looks promising. Even though there is a keyboard scanning routine in the firmware, I don't want to use that unless absolutely necessary.

During keyboard testing, I noticed just how slow the screen_write function is. Since I intend to do a lot of printing, I need this to be as fast as possible. Or at least reasonably quick.

To that end, I'm running a speed test here. This is the time, in seconds it takes to count up to 0xA00. Time is taken on a non-maximied screen, started when "2" is pressed on the TI program selection screen.

TIME Description
106.17 Baseline
57.23 No copy from VDP for screen scroll
83.13 First attempt with screen buffer, non-working

The savings seems to be in the scrolling section. By using word copies instead of byte copies, I seem to gain a bit of speed. Unfortunately, what was a reasonably well laid out bit of code will be mangled by maintainng the screen buffer. Oh well. I'd rather have the 20% speed-up.