class Assembler:
def __init__(self):
self._code = Code()
self._lexer = Lexer()
self._parser = Parser()
self._symbol_table = SymbolTable()
def assemble(self, path):
# Read file content
content = self._read_file_contents(path)
# Lex the file contents
self._lexer.lex(content)
# Pass the tokens to ther parser
self._parser.set_tokens(self._lexer.tokens())
# Build symbols
self._build_symbols()
# Translate to symbolless asm
self._write_symbolless_asm(path)
# Translate binary
self._write_binary(path)
def _write_symbolless_asm(self, path):
basename = os.path.basename(path)
name = basename.rsplit('.asm', 1)[0]
file = open('%s/%sL.asm' % (os.path.dirname(path), name), 'w')
self._parser.reset_pos()
while self._parser.has_commands():
command_type = self._parser.command_type()
if command_type is Command.L_COMMAND:
self._parser.advance()
continue
elif command_type is Command.A_COMMAND:
value = None
symbol = self._parser.symbol()
if symbol is not None:
value = self._symbol_table.get_address(symbol)
if value is None:
sys.stderr.write('[Assembler]: Symbol not defined %s' %
symbol)
file.close()
sys.exit(1)
else:
value = self._parser.value()
file.write('@%s' % value)
elif command_type in [
Command.C_COMMAND_JMP, Command.C_COMMAND_COMP
]:
file.write(self._parser.text())
file.write('\n')
self._parser.advance()
file.close()
def _write_binary(self, path):
basename = os.path.basename(path)
name = basename.rsplit('.asm', 1)[0]
file = open('%s/%s.hack' % (os.path.dirname(path), name), 'w')
binary = self._translate()
file.write(binary)
file.close()
def _build_symbols(self):
symbols_count = 0
self._init_symbol_table()
# First pass - get label symbols
while self._parser.has_commands():
if self._parser.command_type() is Command.L_COMMAND:
symbol = self._parser.symbol()
if self._symbol_table.contains(symbol):
sys.stderr.write(
'[Assembler]: Symbol %s is used more than once' %
symbol)
sys.exit(1)
address = self._parser.pos() - symbols_count
self._symbol_table.add_entry(symbol, address)
symbols_count += 1
self._parser.advance()
# Second pass - get variable symbols
variable_address = 16
self._parser.reset_pos()
while self._parser.has_commands():
command_type = self._parser.command_type()
if command_type is Command.A_COMMAND:
symbol = self._parser.symbol()
if symbol is not None and \
not self._symbol_table.contains(symbol):
address = variable_address
self._symbol_table.add_entry(symbol, address)
variable_address += 1
self._parser.advance()
def _translate(self):
output = ''
self._parser.reset_pos()
while self._parser.has_commands():
command_type = self._parser.command_type()
if command_type is Command.A_COMMAND:
symbol = self._parser.symbol()
if symbol is not None:
if not self._symbol_table.contains(symbol):
sys.stderr.write('[Assembler]: Unknown symbol: %s' %
symbol)
sys.exit(1)
address = self._symbol_table.get_address(symbol)
output += self._to_binary(address) + '\n'
else:
value = self._parser.value()
output += self._to_binary(int(value)) + '\n'
elif command_type is Command.C_COMMAND_COMP:
comp = self._code.comp(self._parser.comp())
dest = self._code.dest(self._parser.dest())
output += '111' + comp + dest + '000\n'
elif command_type is Command.C_COMMAND_JMP:
comp = self._code.comp(self._parser.comp())
jump = self._code.jump(self._parser.jump())
output += '111' + comp + '000' + jump + '\n'
self._parser.advance()
return output
def _init_symbol_table(self):
self._symbol_table.clear()
entries = {
'SP': 0,
'LCL': 1,
'ARG': 2,
'THIS': 3,
'THAT': 4,
'SCREEN': 16384,
'KBD': 24576,
}
# R0 to R15
for address in range(16):
entries['R%d' % address] = address
# Initialize symbol table with predefined symbols
for key, value in entries.items():
self._symbol_table.add_entry(key, value)
def _read_file_contents(self, path):
file = open(path, 'r')
content = file.read()
file.close()
return content
def _to_binary(self, value):
return format(value, '016b')
