bcs

snes-core/src/cpu/instructionstemp/bcs.rs

@@ -0,0 +1,67 @@
+use crate::cpu::{bus::Bus, registers::Registers};
+
+use crate::cpu::cycles;
+use super::{CPUInstruction, Decode};
+use super::decoder_common;
+use super::branch_common;
+
+static INSTR_NAME: &'static str = "BCS";
+
+pub struct BCS {}
+
+impl CPUInstruction for BCS {
+    fn execute(&self, registers: &mut Registers, bus: &mut Bus) {
+        let nearlabel = bus.read(registers.get_pc_address().wrapping_add(1));
+        let (bytes, cycles) = cycles::increment_cycles_branch();
+        registers.increment_pc(bytes); registers.cycles += cycles;
+        if registers.get_carry_flag() {
+            let page_boundary_crossed = branch_common::do_branch(nearlabel, registers);
+            let (bytes, cycles) = cycles::increment_cycles_branch_taken(page_boundary_crossed);
+            registers.increment_pc(bytes); registers.cycles += cycles;
+        }
+    }
+}
+
+impl Decode for BCS {
+    fn mnemonic(&self, registers: &Registers, bus: &Bus, opcode: u8) -> String {
+        decoder_common::mnemonic_branch_nearlabel(opcode, INSTR_NAME, registers, bus)
+    }
+}
+
+
+#[cfg(test)]
+mod cpu_instructions_tests {
+    use super::*;
+
+    #[test]
+    fn test_bcs() {
+        let instruction = BCS{};
+        // test with positive nearlabel
+        // branch not taken
+        let mut registers = Registers::new();
+        let mut bus = Bus::new();
+        registers.pc = 0x0000;
+        registers.cycles = 0;
+        registers.set_carry_flag(false);
+        bus.write(0x02, 0b00001111);
+        instruction.execute(&mut registers, &mut bus);
+        assert_eq!(registers.pc, 0x02);
+        assert_eq!(registers.cycles, 2);
+        // branch taken
+        registers.pc  = 0x0000;
+        registers.cycles        = 0;
+        registers.set_carry_flag(true);
+        bus.write(0x01, 0b00001111);
+        instruction.execute(&mut registers, &mut bus);
+        assert_eq!(registers.pc, 0x02 + 0b00001111);
+        assert_eq!(registers.cycles, 3);
+        // test with negative nearlabel and boundary cross
+        registers.pc  = 0x0100;
+        registers.cycles        = 0;
+        registers.set_carry_flag(true);
+        bus.write(0x101, 0xFB); // write -5
+        instruction.execute(&mut registers, &mut bus);
+        assert_eq!(registers.pc, 0xFD);
+        assert_eq!(registers.cycles, 4);
+    }
+}

snes-core/src/cpu/instructionstemp/mod.rs

@@ -6,6 +6,7 @@ pub mod adc;
 pub mod and;
 pub mod asl;
 pub mod bcc;
+pub mod bcs;
 pub mod decoder_common;
 pub mod branch_common;