Fill.asm screen flickering

[ElliottS]

I've been trying to complete the fill.asm assignment. I thought I had it worked out, but when I run the program and hold down a key the screen seems to 'flicker', changing rapidly between black and white. I am not sure if it is a problem with my code or if the simulator itself was not working properly. Has anyone else had this problem?

Would I be able to post my code here?

[cadet1620]

The flickering you are describing is not a known simulator problem.

There is, however, a bug in the simulator that when you write to the KEYBOARD address, it affects what will be read the next time from KEYBOARD.

Your program may be writing one word beyond the screen. I haven't seen any fill programs that altenate filling white and black caused by this, but I have see programs that are stuck continuously filling white or black.

If you don't find an off-by-one bug bug in your code, feel free to email it to me and I'll let you know what I find.

--Mark

[ElliottS]

Thank you for your response, this is exactly what happend! My code was writing -1 to the keyboard address and this was obviously interfering with my test to determine whether a key was pressed or not. My test to fill used JGT so -1 would Look like no key was pressed and would fill white. I'm guessing that eventually the key I was pressing would re-map to that address and thus the 'flickering' I described.