mirror of
https://github.com/DoctorWkt/pdp7-unix.git
synced 2026-01-22 02:26:34 +00:00
43 lines
1.5 KiB
Plaintext
43 lines
1.5 KiB
Plaintext
Basics of the Unix assembler syntax
|
|
|
|
Lines starting with " are comment lines
|
|
|
|
. is the location counter, where the next code or constant will be placed
|
|
.. is the relocation counter
|
|
|
|
t = 0 Sets a built-in variable to this value without generating any machine code.
|
|
Variables so far are . .. and t. Not sure what t's purpose is yet.
|
|
|
|
orig: is a label. It looks like labels can have dots in them.
|
|
Dots seem to separate structures and fields, e.g. u.base
|
|
but there are some symbols that start with dots, e.g. .seek
|
|
|
|
jms copy; 10; u.rg+2; 6 Semicolons separate instructions and
|
|
word expressions that follow the instruction
|
|
|
|
Some expressions are 0:0, not sure about this.
|
|
Is it two 9-bit fields? No idea
|
|
|
|
jmp 1f Jump back to the closest 1: label
|
|
jmp 1b Jump forward to the closest 1: label
|
|
|
|
Some lines are indented differently to others e.g.
|
|
|
|
jms betwen; o10000; o17762
|
|
jms error
|
|
dac .+1
|
|
|
|
I think this is to indicate the skip logic, but it plays no part in the assembly syntax.
|
|
|
|
-1 occurs instead of instructions, so it looks like the assembler allows
|
|
literal constants at any time.
|
|
|
|
String literals seem to be two characters decorated with < > characters, e.g.
|
|
"ab" is <a>b. I'm guessing these are placed as pairs in one word. The syntax
|
|
is confusing, because I've also seen <no> ; 040 ; <fi> ; <le>; <s 012 which
|
|
appears to mean "no files\n".
|
|
|
|
Looks like a line can contain multiple labels, e.g. o12: d10: 10
|
|
|
|
Numeric literals: 0xx are octal values, [1-9]xx are decimal values.
|