In my previous post I talked about some mysterious code in the macro definitions for the Atari Crystal Castles arcade game source code. Someone responded to my post about this and pointed me to Franz Lanzinger who was one of the original authors of Crystal Castles who in turn pointed me to Dave Shepperd who wrote that assembler. He confirmed that this was a custom assembler developed for Atari:
"Yes, I wrote both versions of mac65. We called it macxx way back when (because it would assemble for the 6502, 65C02, 6800, 68000, and others). The first version was written in PDP11 assembly for RT11 and it used linkm as a linker, the other tool I wrote. We used those tools for a year or so after getting the VAXen. The second and current version was written in C (first DEC C for the VAX, then subsequently others and finally gcc) and compiled on various O/S. I've only been maintaining it on Linux, but it probably will still build on many others, especially those Linux like. Not sure if it would work anymore on 16 bit machines. This version uses another of my tools also written in C: LLF (Link+Locate+Format) as the linker."
He also provided an explanation of how he believes the two mystery lines worked:
.LIST SRC(...S1,1)
The .LIST pseudo op controls what get's output to the listing file. The SRC flag says to turn on the output of the assembler source code and the values in parenthesis after it control the details of the output. The first parameter tells the assembler which columns to start outputting the source on. The second value, if present and not zero, tells the assembler to wait until the next line before changing the output column instead of doing it on the current line.
.PRINT ..NST$(37,1,16,1,38'->')
The .PRINT pseudo op prints text to the listing file. The expression after .PRINT is evaluated and the result it what will be printed. Again, we have a list of parameters to control this output. This is a pretty esoteric command so I am not sure if I would have every figured this out:
37 = Column to start the print on
1 = How many characters of the value to print out
16 = The radix of the value, in this case it will be printed as hexadecimal
1 = If present and non-zero, print the leading zeros
38=This parameters is usually used to indicate that the sign should be output, but since it has a text string after it it functions differently. In this case the text "->" will be output starting at column 38.
Let's look at the end result of all of this. Here is a chunk of source code using two nested IF macros:
INX
IFEQ
LDX 40
ENDIF
DEY
ENDIF
The listing output would end up looking something like this:
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