# MIT License
#
# Copyright (c) 2023 Neil Webber
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# FUNCTIONALITY DISCLAIMER:
# This is NOT meant to recreate the entire idea of a PDP-11 assembler.
# Rather, it is meant as an ad-hoc assistance for creating and
# debugging small test programs, of the sort that are found in pdptest.
# As such, the methods here are written on an "as-needed" basis and
# are focused around helping to create hand-constructed test code.
#
from contextlib import AbstractContextManager
class PDP11InstructionAssembler:
B6MODES = {}
_rnames = [(f"R{_i}", _i) for _i in range(8)] + [("SP", 6), ("PC", 7)]
for _rn, _i in _rnames:
B6MODES[f"{_rn}"] = _i # register direct
B6MODES[f"({_rn})"] = 0o10 | _i # register indirect
B6MODES[f"({_rn})+"] = 0o20 | _i # autoincrement
B6MODES[f"@({_rn})+"] = 0o30 | _i # autoincr deferred
B6MODES[f"-({_rn})"] = 0o40 | _i # autodecrement
B6MODES[f"@-({_rn})"] = 0o50 | _i # autodecr deferred
del _i, _rn, _rnames
# see _InstBlock for explanation of 'with' syntax use
@classmethod
def instruction_block(cls):
return _InstBlock()
def immediate_value(self, s):
base = 8
if s[-1] == '.':
base = 10
s = s[:-1]
val = int(s, base)
# as a convenience, allow negative values and convert them
if val < 0 and val >= -32768:
val += 65536
if val > 65535 or val < 0:
raise ValueError(f"illegal value '{s}' = {val}")
return val
# this is a notational convenience to create a f'*${i].' string
# for an operand that is an immediate deferred (i.e., numeric pointer)
def ptr(self, i):
return f'*${i}.'
def operand_parser(self, operand_string, /):
"""Parse operand_string ('r1', '-(sp)', '4(r5)', $177776, etc).
Returns: sequence: [6 bit code, additional words ...]
Raises ValueError for syntax errors.
Literals that should become (pc)+ (mode 0o27) must start with '$'
They will be octal unless they end with a '.'
Literals that are pointers and should become @(pc)+ must
start with '*$' and will be octal unless they end with a '.'
An integer, i, can be passed in directly; it is becomes f"${i}."
"""
# NOTE: Not all forms implemented yet. See FUNCTIONALITY DISCLAIMER.
# for convenience
def valerr():
return ValueError(f"cannot parse '{operand_string}'")
# normalize the operand, upper case for strings, turn ints back
# into their corresponding string (roundabout, but easiest)
try:
operand = operand_string.upper()
except AttributeError:
operand = f"${operand_string}."
# bail out if spaces in middle, and remove spaces at ends
s = operand.split()
if len(s) > 1:
raise valerr()
operand = s[0]
# operand now fully normalized: upper case, no spaces.
# the first/easiest to try is to see if it is an immediate.
# It will (must) start with either '$', or '*$' if so.
try:
if operand[0] == '$':
return [0o27, self.immediate_value(operand[1:])]
elif operand.startswith('*$'):
return [0o37, self.immediate_value(operand[2:])]
except ValueError:
raise valerr() from None
# wasn't immediate, see if it matches the precomputed modes
try:
return [self.B6MODES[operand]]
except KeyError:
pass
# last chance: X(Rn) and @X(rn)
# see if X(Rn) or @X(Rn)...
if operand[0] == '@':
mode = 0o70
operand = operand[1:]
else:
mode = 0o60
# for starters, it must contain one '(' so should split to 2
s = operand.split('(')
if len(s) != 2:
raise valerr()
idxval = self.immediate_value(s[0])
# the back end of this, with the '(' put back on,
# must end with ')' and must parse
if s[1][-1] != ')':
raise valerr()
try:
b6 = self.B6MODES['(' + s[1]]
except KeyError:
raise valerr() from None
seq = [mode | (b6 & 0o07), idxval]
return self._seqwords(seq)
# no-op here, but overridden in _Sequence to track generated instructions
def _seqwords(self, seq):
return seq
# All 2 operand instructions end up here eventually
def _2op(self, operation, src, dst):
src6, *src_i = self.operand_parser(src)
dst6, *dst_i = self.operand_parser(dst)
return self._seqwords([operation | src6 << 6 | dst6, *src_i, *dst_i])
# All 1 operand instructions end up here eventually
# This also supports 0 operand "literals" (which are typically
# instructions that have been hand-assembled another way)
def _1op(self, operation, dst):
"""dst can be None for, essentially, a _0op."""
if dst is None:
dst6 = 0
dst_i = []
else:
dst6, *dst_i = self.operand_parser(dst)
return self._seqwords([operation | dst6, *dst_i])
def mov(self, src, dst):
return self._2op(0o010000, src, dst)
def cmp(self, src, dst):
return self._2op(0o020000, src, dst)
def add(self, src, dst):
return self._2op(0o060000, src, dst)
def sub(self, src, dst):
return self._2op(0o160000, src, dst)
def clr(self, dst):
return self._1op(0o005000, dst)
def inc(self, dst):
return self._1op(0o005200, dst)
def dec(self, dst):
return self._1op(0o005300, dst)
def halt(self):
return self.literal(0)
def mtpi(self, dst):
return self._1op(0o006600, dst)
def mfpi(self, src):
return self._1op(0o006500, src)
def mtpd(self, dst):
return self._1op(0o106600, dst)
def mfpd(self, src):
return self._1op(0o106500, src)
def trap(self, tnum):
return self.literal(0o104400 | tnum)
def literal(self, inst, oprnd=None, /):
"""For hand-assembled instructions. Also allows 1 operand."""
return self._1op(inst, oprnd)
# This provides a convenience for just calling the native methods
# while accumulating a list of instructions. For better or for worse,
# instead of:
# insts = (a.mov('r1', 'r2'), a.clr('r0'), ... etc)
#
# a context manager can be used to write it this way:
#
# with ASM.instruction_block() as a:
# a.mov('r1', 'r2')
# a.clr('r0')
# ...
# etc
#
# and then the instructions are obtained via a.instruction_block()
# (not a typo; the WITH is a class method and ^^^^^ is an instance method)
#
# This is sometimes handy if conditional computation or other gyrations
# are needed in the gathering of the instructions
class _InstBlock(PDP11InstructionAssembler, AbstractContextManager):
def __init__(self):
super().__init__()
self._instblock = []
def __enter__(self):
return self
def __exit__(self, *args, **kwargs):
return None
def _seqwords(self, seq):
"""seq can be an iterable, or a naked (integer) instruction."""
try:
self._instblock += seq
except TypeError:
self._instblock += [seq]
return seq
def instruction_block(self):
return self._instblock