153 lines
4.3 KiB
Text
153 lines
4.3 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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.QQ
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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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.LP
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Flags :
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.IP ""
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Opcode type, only one of the following may be specified.
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.RS
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.IP \-
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opcode without argument
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.IP m
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mini
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.IP s
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shortie
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.IP 2
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opcode with 2-byte signed argument
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.IP 4
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opcode with 4-byte signed argument
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.IP 8
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opcode with 8-byte signed argument
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.IP u
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opcode with 2-byte unsigned argument
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.RE
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.IP ""
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Secondary (escaped) opcodes.
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.RS
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.IP 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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.RE
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.IP ""
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restrictions on arguments
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.RS
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.IP N
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Negative arguments only
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.IP P
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Positive and zero arguments only
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.RE
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.IP ""
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mapping of arguments
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.RS
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.IP 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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.IP 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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.RE
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.LP
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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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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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.br
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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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.IP "aar mwPo 1 34"
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.br
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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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.IP "adp sP 1 41"
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.br
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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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.IP "bra sN 2 60"
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.br
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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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.IP "zer e\- 145"
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.br
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Escaped opcode 145 is used for ZER.
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.LP
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The interpreter opcode table:
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.DS
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.so itables
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.DE
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.PP
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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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.LP
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The following suffices exist:
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.TS
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tab(:);
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l l.
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.z:no arguments
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.l:16-bit argument
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.L:32-bit argument
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.u:16-bit unsigned argument
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.lw:16-bit argument divided by the wordsize
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.Lw:32-bit argument divided by the wordsize
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.p:positive 16-bit argument
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.P:positive 32-bit argument
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.pw:positive 16-bit argument divided by the wordsize
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.Pw:positive 32-bit argument divided by the wordsize
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.n:negative 16-bit argument
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.N:negative 32-bit argument
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.nw:negative 16-bit argument divided by the wordsize
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.Nw:negative 32-bit argument divided by the wordsize
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.s<num>:shortie with <num> as high order argument byte
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.w<num>:shortie with argument divided by the wordsize
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.<num>:mini with <num> as argument
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.<num>W:mini with <num>*wordsize as argument
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.TE
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.LP
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<num> is a possibly negative integer.
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.LP
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The dispatch table for the 256 primary opcodes:
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.sp 1
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.so dispat1
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.sp 2
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The list of secondary opcodes (escape1):
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.sp 1
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.so dispat2
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.sp 2
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Finally, the list of opcodes with four byte arguments (escape2).
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.sp 1
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.so dispat3
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