Add dummy read for pha and php

evilcorpltd · Oct 1, 2020 · ff31bd9 · ff31bd9
1 parent 5ed58ea
commit ff31bd9
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Showing 2 changed files with 12 additions and 2 deletions.
diff --git a/core/src/mos6502.cpp b/core/src/mos6502.cpp
@@ -121,7 +121,9 @@ Pipeline Mos6502::parse_next_instruction() {
                 create_left_shift_instruction(*state_.current_opcode, false));
         break;
     case Instruction::PhpImplied:
-        result.push([] { /* Do nothing. */ });
+        result.push([this] { /* dummy read */
+            mmu_->read_byte(registers_->pc);
+        });
         result.push([this] { stack_.push_byte(registers_->p | B_FLAG); });
         break;
     case Instruction::BplRelative:
@@ -198,7 +200,9 @@ Pipeline Mos6502::parse_next_instruction() {
                 create_right_shift_instruction(*state_.current_opcode, false));
         break;
     case Instruction::PhaImplied:
-        result.push([] { /* Do nothing. */ });
+        result.push([this] { /* dummy read */
+            mmu_->read_byte(registers_->pc);
+        });
         result.push([this] { stack_.push_byte(registers_->a); });
         break;
     case Instruction::JmpAbsolute:

diff --git a/core/test/src/test_cpu.cpp b/core/test/src/test_cpu.cpp
@@ -52,6 +52,8 @@ TEST_F(CpuTest, state_is_initialized) {
 TEST_F(CpuTest, state_opcode_returns_instruction) {
     registers.pc = 0x1234;
     stage_instruction(PHP);
+    // Dummy read
+    EXPECT_CALL(mmu, read_byte(0x1235));
     step_execution(1);
 
     const CpuState state = cpu->state();
@@ -159,6 +161,8 @@ TEST_F(CpuTest, php_sets_b_flag) {
     expected.sp = 0x09;
     expected.p = registers.p;
 
+    // Dummy read
+    EXPECT_CALL(mmu, read_byte(expected.pc));
     EXPECT_CALL(
             mmu, write_byte(kStackOffset + registers.sp, registers.p | B_FLAG));
 
@@ -282,6 +286,8 @@ TEST_F(CpuTest, pha) {
     registers.sp = 0x05;
     registers.a = 0x84;
 
+    // Dummy read
+    EXPECT_CALL(mmu, read_byte(expected.pc));
     EXPECT_CALL(mmu, write_byte(kStackOffset + registers.sp, registers.a));
 
     expected.sp = 0x04;