sjgray / osi-monitor-roms Goto Github PK

I am usiing this assembler listing with my home built 6502 system. In may ways it duplicates the Ohio superboard I had years ago.
Major difference is rearranging all IO to be in the $Dxxx segment and uing a PS2 keyboard instead of the original scanned matrix. (Interface is similar to ACIA)
To the problem( about 80 lines down):
The screen is still 1k at $D000-$D3FF but the assembler listing calculation does not give the correct result.

SWIDTH	=	COLS-1
TOP	=	SCREEN+START
BASE	=	ROWS-1*WIDTH+TOP
BOT	=	SIZE+1*1024+SCREEN

For my board: SCREEN = $D000, WIDTH = 32, SIZE =0, START =69, COLS = 24. ROWS = 26
The calculations give (verified by examining the output file):
SWIDTH = 23
TOP = $D045
BASE = $D03F
BOT = $D400

The calculation for BASE gives $D035 which is clearly (now) not correct and gave some strange results.
The formula should have been (NB parentheses):
BASE = (ROWS-1) * WIDTH + TOP which gives $D365 and works correctly.
As it happens the formula for BOT was OK for my system (accidental) but it should be:
BOT = (SIZE+1) * 1024 + SCREEN
Admittably I am not using the same assembler but I would assume that the normal arithmetic precedence rules would be followed. (Mine is VASM oldstyle)
I think this may also apply to other listings.
Hope that is useful
Phil