116 lines
4.2 KiB
Python
116 lines
4.2 KiB
Python
# MIT License
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#
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# Copyright (c) 2023 Neil Webber
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# FUNCTIONALITY DISCLAIMER:
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# This is NOT meant to recreate the entire idea of a PDP-11 assembler.
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# Rather, it is meant as an ad-hoc assistance for creating and
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# debugging small test programs, of the sort that are found in pdptest.
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# As such, the methods here are written on an "as-needed" basis and
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# are focused around helping to create hand-constructed test code.
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#
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class PDP11InstructionAssembler:
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def __init__(self):
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# crude but so so easy .. translate string to 6-bit operand mode
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self.B6MODES = {}
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for i in range(8):
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rnames = [f"R{i}"]
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if i == 6:
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rnames.append("SP")
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elif i == 7:
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rnames.append("PC")
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for rn in rnames:
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self.B6MODES[f"{rn}"] = i # register direct
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self.B6MODES[f"({rn})"] = 0o10 | i # register indirect
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self.B6MODES[f"({rn})+"] = 0o20 | i # autoincrement
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self.B6MODES[f"@({rn})+"] = 0o30 | i # autoincr deferred
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self.B6MODES[f"-({rn})"] = 0o40 | i # autodecrement
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self.B6MODES[f"@-({rn})"] = 0o50 | i # autodecr deferred
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# X(Rn) and @X(Rn) cannot be parsed this simple lookup way
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def operand_parser(self, operand_string, /):
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"""Parse operand_string ('r1', '-(sp)', '4(r5)', etc).
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Returns: sequence: [6 bit code, additional words ...]
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Raises ValueError for syntax errors.
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"""
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# NOTE: Not all forms implemented yet. See FUNCTIONALITY DISCLAIMER.
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# normalize the operand
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operand = operand_string.upper()
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s = operand.split() # this also removes leading/trailing space
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if len(s) > 1: # but if there were middle spaces... no good
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raise ValueError(f"more than one word in '{operand_string}'")
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operand = s[0]
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# operand should be fully normalized: upper case, no spaces.
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try:
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return [self.B6MODES[operand]]
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except KeyError:
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pass
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# for convenience
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def valerr():
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return ValueError(f"cannot parse '{operand_string}'")
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# see if X(Rn) or @X(Rn)...
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if operand[0] == '@':
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mode = 0o70
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operand = operand[1:]
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else:
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mode = 0o60
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# for starters, it must contain one '(' so should split to 2
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s = operand.split('(')
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if len(s) != 2:
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raise valerr()
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idxstr = s[0]
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# idxstr can only end with a digit or a '.' ... in particular
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base = 8
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if idxstr[-1] == '.':
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base = 10
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idxstr = idxstr[:-1]
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elif not idxstr[-1].isdigit():
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raise valerr()
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idxval = int(idxstr, base)
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# the back end of this, with the '(' put back on,
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# must end with ')' and must parse
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if s[1][-1] != ')':
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raise valerr()
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try:
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b6 = self.B6MODES['(' + s[1]]
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except KeyError:
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raise valerr() from None
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return [mode | (b6 & 0o07), idxval]
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