155 lines
4.1 KiB
Text
155 lines
4.1 KiB
Text
.BP
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.AP "EM CODE TABLES"
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The following table is used by the assembler for EM machine
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language.
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It specifies the opcodes used for each instruction and
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how arguments are mapped to machine language arguments.
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The table is presented in three columns,
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each line in each column contains three or four fields.
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Each line describes a range of interpreter opcodes by
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specifying for which instruction the range is used, the type of the
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opcodes (mini, shortie, etc..) and range for the instruction
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argument.
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.A
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The first field on each line gives the EM instruction mnemonic,
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the second field gives some flags.
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If the opcodes are minis or shorties the third field specifies
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how many minis/shorties are used.
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The last field gives the number of the (first) interpreter
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opcode.
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.N 1
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Flags :
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.IS 3
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.N 1
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Opcode type, only one of the following may be specified.
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.PS - 5 " "
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.PT \-
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opcode without argument
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.PT m
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mini
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.PT s
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shortie
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.PT 2
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opcode with 2-byte signed argument
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.PT 4
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opcode with 4-byte signed argument
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.PT 8
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opcode with 8-byte signed argument
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.PT u
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opcode with 2-byte unsigned argument
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.PE
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Secondary (escaped) opcodes.
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.PS - 5 " "
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.PT e
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The opcode thus marked is in the secondary opcode group instead
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of the primary
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.PE
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restrictions on arguments
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.PS - 5 " "
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.PT N
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Negative arguments only
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.PT P
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Positive and zero arguments only
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.PE
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mapping of arguments
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.PS - 5 " "
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.PT w
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argument must be divisible by the wordsize and is divided by the
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wordsize before use as opcode argument.
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.PT o
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argument ( possibly after division ) must be >= 1 and is
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decremented before use as opcode argument
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.PE
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.IE
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If the opcode type is 2,4 or 8 the resulting argument is used as
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opcode argument (least significant byte first).
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.N
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If the opcode type is mini, the argument is added
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to the first opcode \- if in range \- .
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If the argument is negative, the absolute value minus one is
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used in the algorithm above.
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.N
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For shorties with positive arguments the first opcode is used
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for arguments in the range 0..255, the second for the range
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256..511, etc..
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For shorties with negative arguments the first opcode is used
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for arguments in the range \-1..\-256, the second for the range
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\-257..\-512, etc..
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The byte following the opcode contains the least significant
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byte of the argument.
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First some examples of these specifications.
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.PS - 5
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.PT "aar mwPo 1 34"
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Indicates that opcode 34 is used as a mini for Positive
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instruction arguments only.
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The w and o indicate division and decrementing of the
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instruction argument.
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Because the resulting argument must be zero ( only opcode 34 may be used
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), this mini can only be used for instruction argument 2.
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Conclusion: opcode 34 is for "AAR 2".
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.PT "adp sP 1 41"
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Opcode 41 is used as shortie for ADP with arguments in the range
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0..255.
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.PT "bra sN 2 60"
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Opcode 60 is used as shortie for BRA with arguments \-1..\-256,
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61 is used for arguments \-257..\-512.
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.PT "zer e\- 145"
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Escaped opcode 145 is used for ZER.
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.PE
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The interpreter opcode table:
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.N 1
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.IS 3
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.so itables
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.IE
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.P
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The table above results in the following dispatch tables.
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Dispatch tables are used by interpreters to jump to the
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routines implementing the EM instructions, indexed by the next opcode.
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Each line of the dispatch tables gives the routine names
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of eight consecutive opcodes, preceded by the first opcode number
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on that line.
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Routine names consist of an EM mnemonic followed by a suffix.
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The suffices show the encoding used for each opcode.
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.N
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The following suffices exist:
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.N 1
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.VS 1 0
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.IS 4
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.PS - 11
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.PT .z
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no arguments
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.PT .l
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16-bit argument
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.PT .lw
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16-bit argument divided by the wordsize
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.PT .p
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positive 16-bit argument
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.PT .pw
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positive 16-bit argument divided by the wordsize
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.PT .n
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negative 16-bit argument
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.PT .nw
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negative 16-bit argument divided by the wordsize
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.PT .s<num>
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shortie with <num> as high order argument byte
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.PT .w<num>
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shortie with argument divided by the wordsize
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.PT .<num>
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mini with <num> as argument
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.PT .<num>W
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mini with <num>*wordsize as argument
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.PE 1
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<num> is a possibly negative integer.
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.VS 1 1
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.IE
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The dispatch table for the 256 primary opcodes:
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.N 1
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.so dispat1
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.N 2
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The list of secondary opcodes (escape1):
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.N 1
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.so dispat2
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.N 2
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Finally, the list of opcodes with four byte arguments (escape2).
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.N 1
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.so dispat3
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