Update BRK timings

evilcorpltd · Oct 24, 2019 · 682f467 · 682f467
1 parent 137f6ad
commit 682f467
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Showing 3 changed files with 32 additions and 31 deletions.
diff --git a/core/src/mos6502.cpp b/core/src/mos6502.cpp
@@ -96,14 +96,18 @@ Pipeline Mos6502::parse_next_instruction() {
 
     switch (current_opcode_->instruction) {
     case Instruction::BrkImplied:
-        result.push([=]() { ++registers_->pc; });
         result.push([=]() {
-            /* Do nothing. */
+            // Dummy read
+            mmu_->read_byte(registers_->pc++);
         });
-        result.push([=]() { stack_.push_word(registers_->pc); });
+        result.push([=]() { stack_.push_byte(registers_->pc >> 8); });
+        result.push([=]() { stack_.push_byte(registers_->pc & 0xFF); });
         result.push([=]() { stack_.push_byte(registers_->p | B_FLAG); });
-        result.push([=]() { ++registers_->pc; });
-        result.push([=]() { registers_->pc = mmu_->read_word(kBrkAddress); });
+        result.push([=]() { tmp_ = mmu_->read_byte(kBrkAddress); });
+        result.push([=]() {
+            const uint16_t pch = mmu_->read_byte(kBrkAddress + 1) << 8;
+            registers_->pc = pch | tmp_;
+        });
         break;
     case Instruction::PhpImplied:
         result.push([=]() {

diff --git a/core/test/src/test_cpu.cpp b/core/test/src/test_cpu.cpp
@@ -127,7 +127,9 @@ class CpuTest : public ::testing::Test {
             : registers(),
               mmu(),
               cpu{CpuFactory::create_mos6502(&registers, &mmu)},
-              expected() {}
+              expected() {
+        registers.sp = expected.sp = 0xFF;
+    }
 
     void stage_instruction(uint8_t instruction) {
         expected.pc += 1;
@@ -658,23 +660,23 @@ TEST_F(CpuTest, unsupported_instruction) {
 }
 
 TEST_F(CpuTest, brk) {
+    registers.pc = 0x1234;
     stage_instruction(BRK);
     expected.pc = 0xDEAD;
 
-    const uint8_t expected_pc_stack_addr = expected.sp - 1;
-    const uint8_t expected_p_stack_addr = expected_pc_stack_addr - 1;
-
     expected.sp -= 2 + 1; // 1 word and 1 byte
 
-    ON_CALL(mmu, read_word(kBrkAddress)).WillByDefault(Return(0xDEAD));
+    // Dummy read
+    EXPECT_CALL(mmu, read_byte(0x1235));
+
+    EXPECT_CALL(mmu, read_byte(kBrkAddress)).WillOnce(Return(0xAD));
+    EXPECT_CALL(mmu, read_byte(kBrkAddress + 1)).WillOnce(Return(0xDE));
 
     // First the return address is pushed and then the registers.
+    EXPECT_CALL(mmu, write_byte(kStackOffset + registers.sp, 0x12));
+    EXPECT_CALL(mmu, write_byte(kStackOffset + registers.sp - 1, 0x36));
     EXPECT_CALL(mmu,
-            write_word(
-                    kStackOffset + expected_pc_stack_addr, registers.pc + 2));
-    EXPECT_CALL(mmu,
-            write_byte(kStackOffset + expected_p_stack_addr,
-                    registers.p | B_FLAG));
+            write_byte(kStackOffset + registers.sp - 2, registers.p | B_FLAG));
 
     step_execution(7);
 

diff --git a/core/test/src/test_cpuintegration.cpp b/core/test/src/test_cpuintegration.cpp
@@ -91,7 +91,8 @@ TEST_F(CpuIntegrationTest, simple_program) {
                     0x8c,
                     0x02,
                     0x04,
-                    0x00});
+                    0x00,
+                    0x00}); // Needed for previous BRK dummy read
     set_reset_address(0x0600);
     set_break_address(0xDEAD);
 
@@ -134,7 +135,8 @@ TEST_F(CpuIntegrationTest, branch) {
                     0x8e,
                     0x01,
                     0x02,
-                    0x00});
+                    0x00,
+                    0x00}); // Needed for previous BRK dummy read
 
     set_reset_address(0x0600);
     set_break_address(0xDEAD);
@@ -189,25 +191,18 @@ TEST_F(CpuIntegrationTest, stack) {
                     0xd0,
                     0xf5,
                     0x68});
-    load_hex_dump(0x0600,
-            {0xa2,
-                    0x00,
-                    0xa0,
-                    0x00,
-                    0x8a,
-                    0x99,
+    load_hex_dump(0x0610,
+            {0x99,
                     0x00,
                     0x02,
-                    0x48,
-                    0xe8,
                     0xc8,
                     0xc0,
-                    0x10,
+                    0x20,
                     0xd0,
-                    0xf5,
-                    0x68});
-    load_hex_dump(
-            0x0610, {0x99, 0x00, 0x02, 0xc8, 0xc0, 0x20, 0xd0, 0xf7, 0x00});
+                    0xf7,
+                    0x00,
+                    0x00,
+                    0x00}); // Needed for previous BRK dummy read
 
     // STA with absolute indexed addressing will first read from the effective
     // address before writing to it, so we need to initialize the fake mmu with