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as: add some docs on MACRO-10 syntax
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Mikael Pettersson
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erlang/apps/as/doc/macro10.txt
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erlang/apps/as/doc/macro10.txt
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MACRO-10 Assembler Syntax
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*************************
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This is a brief summary of the basic lexical and syntactic elements
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of the MACRO-10 Assembler. Directives and macros are not covered.
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Numbers
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=======
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Numbers are in octal by default.
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The default number radix can be changed using the RADIX pseudo-op.
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A single-digit number is always interpreted as radix 10, that is,
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"9" denotes decimal 9 not an error even if RADIX is 8 or 2.
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The radix of a number can also be specified by prefixing the number
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with ^B for binary, ^O for octal, or ^D for decimal. (These are two-
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character sequences "up-arrow" "B" etc, not control characters.)
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Hexadecimal radix is not supported.
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The K, M, and G suffixes append 3, 6, or 9 zeros, respectively, to
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a number. (This has surprising effects outside of RADIX 10.)
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Floating-point numbers are expressed in decimal with a mandatory decimal
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point and optional exponent, e.g. 3.14, 3.14E9, 3.14E-7, -3.14E+7.
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A "Bn" suffix shifts the number left by 35-n bits. Excess bits are lost.
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E.g. "1B17" is "000001 000000".
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Using the "_" infix binary operator in an expression "X_Y" shifts X Y bits
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to the left if Y is non-negative, and -Y bits to the right if Y is negative.
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The operands X and Y may be any expressions, including symbols.
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Prefixing a number by ^L (a two-character sequence, not a control character)
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yields the number of leading zeros in the binary representation of the number.
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E.g., ^L0 generates 36 decimal, ^L153 generates 29 decimal, and ^L-153 generates 0.
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Literals
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========
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A literal is a piece of code within square brackets. The enclosed code is
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emitted to the literals pool (normally at the end of the program), and the
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literal is replaced by the code's address.
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Literals can be nested.
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A dot (".") in a literal refers to the statement containing the outermost
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literal.
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Symbols
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=======
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Symbols may be composed of letters, digits, dots ("."), dollar signs ("$"),
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and percent signs ("%"). Other characters are considered delimiters.
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A symbol may not start with a digit.
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If the first character is a dot, the second must not be a digit or another dot.
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(MACRO-10 may generate symbols starting with two dots.)
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Only the first six characters are significant.
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Labels
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------
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A symbol in the first (left-most) field of a statement suffixed by a colon (":")
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defines a label for that location. A dobule colon ("::") marks the label internal.
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There may be more than one label in a statement. Labels may not be redefined.
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Direct-Assignment Symbols
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-------------------------
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A symbol is created and associated with a value using "symbol=expression" or
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"symbol=:expression" (in this case the symbol is internal). These symbols may
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be redefined at any time.
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Variable Symbols
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----------------
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Suffixing a symbol with a number sign ("#") makes it a variable symbol. Such
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symbols are allocated by the assembler, either following the literals pool, or
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into the code via VAR pseudo-ops.
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Symbol Visibility
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-----------------
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Symbols are marked local (INTERNAL) visa the INTERN pseudo-op, or by following
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the label or direct-assignment definition with an extra colon, i.e., "::" or "=:".
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Symbols are marke global (EXTERNAL) via the EXTERN pseudo-op, or by mentioning
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the symbol at least once with a "##" suffix, .e.g. FLAG7## .
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Expressions
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===========
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Numbers and symbols can be combined with arithmetic and logical operators, or grouped
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between angle brackets "<" and ">" to form expressions.
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Operators
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---------
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The infix binary arithmetic operators are "+" (addition), "-" (subtraction),
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"*" (multiplication), and "/" (division).
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The infix binary logical operators are "&" (bit-wise and), "!" (bit-wise or), and
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^!" (bit-wise xor), while "^-" is the bit-wise one's complement prefix operator.
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The infix binary operator ",," combines the low 18 bits of its operands to form a
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36-bit word.
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All operators operate on and generate 36-bit values.
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Priority
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--------
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Unary operations and shifts have highest priority: "+", "-", "^-", "^D", "^O",
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"^B", "B" (binary shift), "_" (underscore shift, "^F", "^L", "E", "K", "M", "G".
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The K, M, and G operations are performed first.
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Logical binary operations have second-highest priority, and are evaluated left to
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right: "!", "^!", "&".
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Multiplicative operations have second-lowest priority, and are evaluated left to
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right: "*", "/".
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Additive operations have lowest priority: "*", "-".
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Strings
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=======
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String operands to data emitting directives, such as ASCII, ASCIZ, COMMENT,
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or SIXBIT, use user-selectable delimiters: DtextD, .e.g, /foo/ or "bar". The
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delimiter cannot be a blank, and it cannot be quoted inside the text.
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A string of at most five 7-bit ASCII characters can be assembled into a single
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left-justified word, by enclosing it with double quotes, "text".
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A string of at most six SIXBIT characters can be assembled into a single
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left-justified word, by exclosing it with single quotes, 'text'.
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Comments
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========
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A comment starts with a semi-colon ";" and extends to the end of the line.
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A comment extends to the next line if the first line ends with CTRL-_ (control
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underscore, ASCII 037), followed by CR-LF.
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Instruction Statements
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======================
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The general form of an instruction statement is
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label: mnemonic accumulator,address ; comment
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or label: mnemonic accumulator, ; comment
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or label: mnemonic address ; comment
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An address may be prefixed with "@" to indicate indirect addressing, and/or
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suffixed by an index register with parentheses "(indexreg)" to indicate
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indexed addressing. E.g.,
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ADD 17,@100(3)
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Either operand may be a symbol or an expression.
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Absent operands are treated as all-bits-zeros.
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I/O instructions are similar, except the "accumulator" operand is replaced by
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a "device" operand, and the binary layout is different.
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There cannot be more than one instruction statement in a line.
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References
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==========
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DECSYSTEM20 MACRO ASSEMBLER Reference Manual, AA-4159C-TM, Apr. 1978.
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DECSYSTEM10 MACRO ASSEMBLER Reference Manual, AA-C780C-TB, Apr. 1978.
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MACRO-6 Assembly Language Programming Manual, DEC-6-0-TP-MAC-LM-FP-ACT01, Feb. 1965.
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