def get_by_identifier(self, identifier, is_word=False):
"""
Gets the value of a register, Flash, or RAM by its name, or address.
For example, get_by_identifier('A') returns the value in the accumulator,
and get_by_identifier(0x01) returns the value in ram[1].
"""
#assume we're working with words for word-size registers
if identifier in ('SP', 'PC'):
is_word = True
#if we've been instructed to retrieve the operator HX, then do so
if identifier == 'HX':
return self.get_HX()
#if the identifier is an integer, use it as a memory address
elif isinstance(identifier, int):
#if the address is in RAM, return the appropriate value
if identifier in self.ram:
#if we've been asked to retrieve a word, do so
if is_word:
return merge_word(self.ram[identifier],
self.ram[identifier + 1])
#otherwise, return a byte
else:
return self.ram[identifier]
#do the same for an address in flash
elif identifier in self.flash:
#if we've been asked to retrieve a word, do so
if is_word:
return merge_word(self.flash[identifier],
self.flash[identifier + 1])
#otherwise, return a byte
else:
return self.flash[identifier]
#if the address was neither in flash nor RAM, throw an exception
else:
raise InvalidMemoryException(
'One of your instructions tried to read from address ' +
repr(identifier) +
', which isn\'t a valid memory address.')
#if the identifier is a register name, return the register's contents
elif identifier in self.REGISTERS or identifier in self.FLAGS or identifier in self.EXPOSED_PROPERTIES:
return self.__dict__[identifier]
else:
raise ExecutionException(
'The CPU tried to read from a non-existant register ' +
repr(identifier) +
'. This is likely an issue with the simulator; please bring this error to an instructor\'s attention.'
)
def get_by_identifier(self, identifier, is_word=False):
"""
Gets the value of a register, Flash, or RAM by its name, or address.
For example, get_by_identifier('A') returns the value in the accumulator,
and get_by_identifier(0x01) returns the value in ram[1].
"""
#assume we're working with words for word-size registers
if identifier in ('SP', 'PC'):
is_word = True
#if we've been instructed to retrieve the operator HX, then do so
if identifier == 'HX':
return self.get_HX()
#if the identifier is an integer, use it as a memory address
elif isinstance(identifier, int):
#if the address is in RAM, return the appropriate value
if identifier in self.ram:
#if we've been asked to retrieve a word, do so
if is_word:
return merge_word(self.ram[identifier], self.ram[identifier + 1])
#otherwise, return a byte
else:
return self.ram[identifier]
#do the same for an address in flash
elif identifier in self.flash:
#if we've been asked to retrieve a word, do so
if is_word:
return merge_word(self.flash[identifier], self.flash[identifier + 1])
#otherwise, return a byte
else:
return self.flash[identifier]
#if the address was neither in flash nor RAM, throw an exception
else:
raise InvalidMemoryException('One of your instructions tried to read from address ' + repr(identifier) + ', which isn\'t a valid memory address.')
#if the identifier is a register name, return the register's contents
elif identifier in self.REGISTERS or identifier in self.FLAGS or identifier in self.EXPOSED_PROPERTIES:
return self.__dict__[identifier]
else:
raise ExecutionException('The CPU tried to read from a non-existant register ' + repr(identifier) + '. This is likely an issue with the simulator; please bring this error to an instructor\'s attention.')
def fetch_word(self):
"""
Fetches the word at the address contained in the system's program counter, then adds two to the program counter, so it points past the end of the read word.
"""
#fetch two bytes, then merge them into a word
return merge_word(self.fetch_byte(), self.fetch_byte())
def get_HX(self):
"""
Returns the value of HX (the system indexing register) as a 16-bit word.
"""
#merge H and X to form HX, the 16-bit indexing register
return merge_word(self.H, self.X)
def fetch_word(self):
"""
Fetches the word at the address contained in the system's program counter, then adds two to the program counter, so it points past the end of the read word.
"""
#fetch two bytes, then merge them into a word
return merge_word(self.fetch_byte(), self.fetch_byte())
def get_HX(self):
"""
Returns the value of HX (the system indexing register) as a 16-bit word.
"""
#merge H and X to form HX, the 16-bit indexing register
return merge_word(self.H, self.X)
def pull_word(self):
"""
Pulls a word from the stack, and returns it.
"""
#pull two bytes from the stack
msb = self.pull_byte()
lsb = self.pull_byte()
#and merge them into a single word
return merge_word(msb, lsb)
def pull_word(self):
"""
Pulls a word from the stack, and returns it.
"""
#pull two bytes from the stack
msb = self.pull_byte()
lsb = self.pull_byte()
#and merge them into a single word
return merge_word(msb, lsb)