303 lines
9.9 KiB
Python
303 lines
9.9 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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from contextlib import AbstractContextManager
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class PDP11InstructionAssembler:
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B6MODES = {}
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_rnames = [(f"R{_i}", _i) for _i in range(8)] + [("SP", 6), ("PC", 7)]
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for _rn, _i in _rnames:
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B6MODES[f"{_rn}"] = _i # register direct
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B6MODES[f"({_rn})"] = 0o10 | _i # register indirect
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B6MODES[f"({_rn})+"] = 0o20 | _i # autoincrement
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B6MODES[f"@({_rn})+"] = 0o30 | _i # autoincr deferred
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B6MODES[f"-({_rn})"] = 0o40 | _i # autodecrement
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B6MODES[f"@-({_rn})"] = 0o50 | _i # autodecr deferred
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del _i, _rn, _rnames
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# see InstructionBlock for explanation of 'with' syntax use
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@classmethod
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def __enter__(cls):
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return InstructionBlock()
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def __exit__(self, *args, **kwargs):
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return None
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def immediate_value(self, s):
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base = 8
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if s[-1] == '.':
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base = 10
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s = s[:-1]
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val = int(s, base)
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# as a convenience, allow negative values and convert them
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if val < 0 and val >= -32768:
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val += 65536
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if val > 65535 or val < 0:
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raise ValueError(f"illegal value '{s}' = {val}")
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return val
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# this is a notational convenience to create a f'*${i].' string
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# for an operand that is an immediate deferred (i.e., numeric pointer)
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def ptr(self, i):
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return f'*${i}.'
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def operand_parser(self, operand_string, /):
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"""Parse operand_string ('r1', '-(sp)', '4(r5)', $177776, etc).
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Returns: sequence: [6 bit code, additional words ...]
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Raises ValueError for syntax errors.
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Literals that should become (pc)+ (mode 0o27) must start with '$'
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They will be octal unless they end with a '.'
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Literals that are pointers and should become @(pc)+ must
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start with '*$' and will be octal unless they end with a '.'
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An integer, i, can be passed in directly; it is becomes f"${i}."
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"""
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# NOTE: Not all forms implemented yet. See FUNCTIONALITY DISCLAIMER.
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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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# normalize the operand, upper case for strings, turn ints back
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# into their corresponding string (roundabout, but easiest)
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try:
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operand = operand_string.upper()
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except AttributeError:
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operand = f"${operand_string}."
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# bail out if spaces in middle, and remove spaces at ends
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s = operand.split()
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if len(s) > 1:
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raise valerr()
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operand = s[0]
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# operand now fully normalized: upper case, no spaces.
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# the first/easiest to try is to see if it is an immediate.
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# It will (must) start with either '$', or '*$' if so.
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try:
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if operand[0] == '$':
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return [0o27, self.immediate_value(operand[1:])]
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elif operand.startswith('*$'):
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return [0o37, self.immediate_value(operand[2:])]
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except ValueError:
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raise valerr() from None
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# wasn't immediate, see if it matches the precomputed modes
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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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# last chance: X(Rn) and @X(rn)
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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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idxval = self.immediate_value(s[0])
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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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# no-op here, but overridden in _Sequence to track generated instructions
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def _seqwords(self, seq):
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return seq
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# All 2 operand instructions end up here eventually
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def _2op(self, operation, src, dst):
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src6, *src_i = self.operand_parser(src)
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dst6, *dst_i = self.operand_parser(dst)
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return self._seqwords([operation | src6 << 6 | dst6, *src_i, *dst_i])
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# All 1 operand instructions end up here eventually
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# This also supports 0 operand "literals" (which are typically
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# instructions that have been hand-assembled another way)
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def _1op(self, operation, dst):
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"""dst can be None for, essentially, a _0op."""
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if dst is None:
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dst6 = 0
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dst_i = []
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else:
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dst6, *dst_i = self.operand_parser(dst)
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return self._seqwords([operation | dst6, *dst_i])
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# XXX the instructions are not complete, this is being developed
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# as needed for pdptests.py
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#
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# ALSO: see InstructionBlock for (primitive) branching support
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#
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def mov(self, src, dst):
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return self._2op(0o010000, src, dst)
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def movb(self, src, dst):
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return self._2op(0o110000, src, dst)
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def cmp(self, src, dst):
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return self._2op(0o020000, src, dst)
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def bic(self, src, dst):
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return self._2op(0o040000, src, dst)
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def add(self, src, dst):
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return self._2op(0o060000, src, dst)
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def sub(self, src, dst):
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return self._2op(0o160000, src, dst)
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def clr(self, dst):
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return self._1op(0o005000, dst)
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def inc(self, dst):
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return self._1op(0o005200, dst)
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def dec(self, dst):
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return self._1op(0o005300, dst)
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def halt(self):
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return self.literal(0)
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def rtt(self):
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return self.literal(6)
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def mtpi(self, dst):
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return self._1op(0o006600, dst)
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def mfpi(self, src):
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return self._1op(0o006500, src)
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def mtpd(self, dst):
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return self._1op(0o106600, dst)
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def mfpd(self, src):
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return self._1op(0o106500, src)
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def trap(self, tnum):
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return self.literal(0o104400 | tnum)
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def literal(self, inst, oprnd=None, /):
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"""For hand-assembled instructions. Also allows 1 operand."""
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return self._1op(inst, oprnd)
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# An InstructionBlock is a thin layer on just accumulating a sequence
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# of results from calling the instruction methods.
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#
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# Instead of:
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# insts = (
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# a.mov('r1', 'r2'),
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# a.clr('r0'),
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# etc ...
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# )
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#
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# The context manager can be used to write it this way:
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#
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# with ASM() as a:
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# a.mov('r1', 'r2')
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# a.clr('r0')
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# etc ...
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#
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# which, subject to opinion, may be notationally cleaner/clearer and also
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# opens the possibility of if/for/etc full programming constructs as needed.
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#
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# A list of instructions in an InstructionBlock can be obtained at any
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# time via: insts = a.instructions()
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#
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class InstructionBlock(PDP11InstructionAssembler, AbstractContextManager):
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def __init__(self):
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super().__init__()
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self._instblock = []
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self.labels = {}
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def _seqwords(self, seq):
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"""seq can be an iterable, or a naked (integer) instruction."""
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try:
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self._instblock += seq
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except TypeError:
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self._instblock += [seq]
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return seq
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def __len__(self):
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"""Returns the length of the sequence in WORDS"""
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return len(self._instblock)
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def label(self, name):
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"""Record the current position as 'name'."""
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curoffs = len(self)
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self.labels[name] = curoffs
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return curoffs
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# Branch instruction support only exists within a given InstructionBlock
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def bxx_offset(self, name1, name2=None):
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"""Generate offset appropriate to Bxx between name1 and name2.
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If name2 is None, generate offset, backwards, from current to name1.
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"""
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# XXX TODO XXX make forward references possible and automate the
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# backpatching even if that gets one step closer
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# to slowly implementing an entire assembler...
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if name2 is None:
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# +255 not 256 because account for the Bxx instruction itself
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offs = self.labels[name1] - len(self) + 255
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else:
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raise ValueError("two name bxx_offset not yet implemented")
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offs8 = offs & 0o377
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if offs8 != offs:
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raise ValueError(f"distance to {name1} too far.")
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return offs8
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def bne(self, name):
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return self.literal(0o001000 | self.bxx_offset(name))
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def instructions(self):
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return self._instblock
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