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condition for adding cycle to indexed addressing modes

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This commit is contained in:
Franco Colmenarez
2022-11-20 17:38:47 -05:00
parent 9fc1fd66d0
commit d00581011f
1 changed files with 36 additions and 4 deletions
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snes-core/src/cpu/cycles.rs
+36 -4
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@@ -1,10 +1,11 @@
use super::cpu::CPU;
use crate::utils::addressing::{AddressingMode};
use crate::utils::addressing::{AddressingMode, IndexRegister};
impl CPU {
pub fn increment_cycles_adc_sbc(&mut self, addressing_mode: AddressingMode) {
type A = AddressingMode;
type I = IndexRegister;
let (mut bytes, mut cycles) = match addressing_mode {
A::Immediate => (2, 2),
A::Absolute => (3, 4),
@@ -41,9 +42,16 @@ impl CPU {
// condition 3: Add 1 cycle if adding index crosses a page boundary
match addressing_mode {
A::AbsoluteIndexed(_) | A::DirectPageIndirectIndexed(_) => {
todo!("Check if index crosses a page boundary")
}
A::AbsoluteIndexed(index) | A::DirectPageIndirectIndexed(index) => {
let page = (self.registers.get_pc_address() - (bytes as u32)) & 0xFF;
let index = match index {
I::X => self.registers.x,
I::Y => self.registers.y,
};
if (page + index as u32) > 0xFF {
cycles += 1
}
},
_ => {},
};
@@ -64,6 +72,8 @@ mod cpu_instructions_tests {
#[test]
fn test_increment_cycles_adc_sbc() {
let mut cpu = CPU::new();
// 16-bit Memory/accumulator flag condition
cpu.registers.pc = 0;
cpu.cycles = 0;
cpu.registers.set_decimal_mode_flag(false);
@@ -79,6 +89,7 @@ mod cpu_instructions_tests {
assert_eq!(cpu.registers.pc, 3);
assert_eq!(cpu.cycles, 3);
// Decimal flag condition
cpu.registers.pc = 0;
cpu.cycles = 0;
cpu.registers.set_16bit_mode(true);
@@ -87,10 +98,12 @@ mod cpu_instructions_tests {
assert_eq!(cpu.registers.pc, 3);
assert_eq!(cpu.cycles, 4);
// Low byte of direct page register other than zero condition
cpu.registers.pc = 0;
cpu.cycles = 0;
cpu.registers.set_16bit_mode(false);
cpu.registers.set_decimal_mode_flag(false);
cpu.registers.d = 0x0000;
cpu.increment_cycles_adc_sbc(AddressingMode::DirectPage);
assert_eq!(cpu.registers.pc, 2);
assert_eq!(cpu.cycles, 3);
@@ -103,5 +116,24 @@ mod cpu_instructions_tests {
cpu.increment_cycles_adc_sbc(AddressingMode::DirectPage);
assert_eq!(cpu.registers.pc, 2);
assert_eq!(cpu.cycles, 4);
// Adding index crosses a page boundary condition
cpu.registers.pc = 0xFE;
cpu.registers.x = 0x0001;
cpu.cycles = 0;
cpu.registers.set_16bit_mode(false);
cpu.registers.set_decimal_mode_flag(false);
cpu.increment_cycles_adc_sbc(AddressingMode::AbsoluteIndexed(IndexRegister::X));
assert_eq!(cpu.registers.pc, 0xFE + 3);
assert_eq!(cpu.cycles, 4);
cpu.registers.pc = 0xFE;
cpu.registers.x = 0x0010;
cpu.cycles = 0;
cpu.registers.set_16bit_mode(false);
cpu.registers.set_decimal_mode_flag(false);
cpu.increment_cycles_adc_sbc(AddressingMode::AbsoluteIndexed(IndexRegister::X));
assert_eq!(cpu.registers.pc, 0xFE + 3);
assert_eq!(cpu.cycles, 5);
}
}