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implemented BRK and RTI

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This commit is contained in:
James Tauber 2011-08-06 21:00:50 -04:00
parent 807f392386
commit accc0a60bd
1 changed files with 44 additions and 7 deletions
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51
applepy.py
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@ -360,11 +360,6 @@ class CPU:
####
# NOP
def NOP(self):
pass
# LOAD / STORE
def LDA(self, operand_address):
@ -633,8 +628,50 @@ class CPU:
self.zero_flag = (self.y_index == value)
self.sign_flag = (self.y_index < 0x80) # @@@ is this right?
# BRK
# RTI
# SYSTEM
def NOP(self):
pass
def BRK(self):
# push PC
pc_hi, pc_lo = divmod(self.program_counter, 0x100)
s = self.STACK_PAGE + self.stack_pointer
self.stack_pointer = (self.stack_pointer - 1) % 0x100
self.memory.write_byte(s, pc_hi)
self.stack_pointer = (self.stack_pointer - 1) % 0x100
self.memory.write_byte(s, pc_lo)
# PHP
status = self.carry_flag | self.zero_flag << 1 | self.interrupt_disable_flag << 2 | self.decimal_mode_flag << 3 | self.break_flag << 4 | 1 << 5 | self.overflow_flag << 6 | self.sign_flag << 7
self.stack_pointer = (self.stack_pointer - 1) % 0x100
self.memory.write_byte(s, status)
self.progress_counter = self.memory.read_word(0xFFFE)
self.break_flag = 1
def RTI(self):
# PLP
self.stack_pointer = (self.stack_pointer + 1) % 0x100
s = self.STACK_PAGE + self.stack_pointer
status = self.memory.read_byte(s)
self.carry_flag = 0 != status & 1
self.zero_flag = 0 != status & 2
self.interrupt_disable_flag = 0 != status & 4
self.decimal_mode_flag = 0 != status & 8
self.break_flag = 0 != status & 16
self.overflow_flag = 0 != status & 64
self.sign_flag = 0 != status & 128
# pull PC
s = self.STACK_PAGE + self.stack_pointer + 1
self.stack_pointer += 2
self.progress_counter = self.memory.read_word(s)
# @@@ IRQ
# @@@ NMI