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implementation of RTS

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This commit is contained in:
Sam M W 2023-04-13 10:23:55 +01:00
parent 7df9160e32
commit 1b90243738
1 changed files with 14 additions and 0 deletions
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14
src/cpu.rs
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@ -409,11 +409,13 @@ impl<M: Bus> CPU<M> {
}
(Instruction::PLA, OpInput::UseImplied) => {
// Pull accumulator
self.pull_from_stack();
let val: u8 = self.pull_from_stack();
self.registers.accumulator = val as i8;
}
(Instruction::PLP, OpInput::UseImplied) => {
// Pull status
self.pull_from_stack();
let val: u8 = self.pull_from_stack();
// The `truncate` here won't do anything because we have a
// constant for the single unused flags bit. This probably
@ -443,6 +445,12 @@ impl<M: Bus> CPU<M> {
CPU::<M>::rotate_right_with_flags(&mut operand, &mut self.registers.status);
self.memory.set_byte(addr, operand);
}
(Instruction::RTS, OpInput::UseImplied) => {
self.pull_from_stack();
let pcl: u8 = self.pull_from_stack();
let pch: u8 = self.fetch_from_stack();
self.registers.program_counter = (((pch as u16) << 8) | pcl as u16).wrapping_add(1);
}
(Instruction::SBC, OpInput::UseImmediate(val)) => {
debug!("subtract with carry immediate: {}", val);
@ -921,6 +929,12 @@ impl<M: Bus> CPU<M> {
self.registers.stack_pointer.increment();
out
}
fn fetch_from_stack(&mut self) -> u8 {
// gets the next value on the stack but does not update the stack pointer
let addr = self.registers.stack_pointer.to_u16();
self.memory.get_byte(addr)
}
}
impl<M: Bus> core::fmt::Debug for CPU<M> {