Merge pull request #225 from johnor/fix-jsr-timings

Use correct timings for Jsr
evilcorpltd · Feb 25, 2020 · 15ae6ae · 15ae6ae
2 parents 34845eb + a1fcae9
commit 15ae6ae
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Showing 3 changed files with 20 additions and 22 deletions.
diff --git a/core/src/mos6502.cpp b/core/src/mos6502.cpp
@@ -53,11 +53,6 @@ void Mos6502::Stack::push_byte(uint8_t byte) {
     mmu_->write_byte(ram_offset_ + registers_->sp--, byte);
 }
 
-void Mos6502::Stack::push_word(uint16_t word) {
-    mmu_->write_word(ram_offset_ + --registers_->sp, word);
-    --registers_->sp;
-}
-
 Mos6502::Mos6502(CpuRegisters *const registers, IMmu *const mmu)
         : registers_(registers),
           mmu_(mmu),
@@ -175,13 +170,22 @@ Pipeline Mos6502::parse_next_instruction() {
         result.push([=]() { clear_flag(C_FLAG); });
         break;
     case Instruction::JsrAbsolute:
-        result.append(create_absolute_addressing_steps(
-                get_memory_access(state_.current_opcode->family)));
+        result.push([=]() { tmp_ = mmu_->read_byte(registers_->pc++); });
         result.push([=]() {
-            /* Do nothing. */
+            /* Internal operation. Do nothing. */
+        });
+        result.push([=]() {
+            const auto pch = static_cast<uint8_t>(registers_->pc >> 8u);
+            stack_.push_byte(pch);
+        });
+        result.push([=]() {
+            const auto pcl = static_cast<uint8_t>(registers_->pc);
+            stack_.push_byte(pcl);
+        });
+        result.push([=]() {
+            const uint16_t pch = mmu_->read_byte(registers_->pc) << 8u;
+            registers_->pc = pch | tmp_;
         });
-        result.push([=]() { stack_.push_word(--registers_->pc); });
-        result.push([=]() { registers_->pc = effective_address_; });
         break;
     case Instruction::BmiRelative:
         result.append(create_branch_instruction(

diff --git a/core/src/mos6502.h b/core/src/mos6502.h
@@ -35,9 +35,7 @@ class Mos6502 : public IMos6502 {
         Stack(CpuRegisters *registers, IMmu *mmu);
 
         uint8_t pop_byte();
-
         void push_byte(uint8_t byte);
-        void push_word(uint16_t word);
 
     private:
         CpuRegisters *const registers_;

diff --git a/core/test/src/test_cpu.cpp b/core/test/src/test_cpu.cpp
@@ -1179,19 +1179,15 @@ TEST_F(CpuTest, clc) {
 }
 
 TEST_F(CpuTest, jsr) {
+    registers.pc = 0x1234;
     stage_instruction(JSR);
     expected.pc = 0xDEAD;
+    expected.sp -= 2; // pc (2 bytes)
 
-    const uint8_t expected_pc_stack_addr =
-            expected.sp - static_cast<uint8_t>(1);
-    expected.sp -= 2; // 1 word
-
-    EXPECT_CALL(mmu, read_byte(registers.pc + 1)).WillOnce(Return(0xAD));
-    EXPECT_CALL(mmu, read_byte(registers.pc + 2)).WillOnce(Return(0xDE));
-
-    EXPECT_CALL(mmu,
-            write_word(
-                    kStackOffset + expected_pc_stack_addr, registers.pc + 2));
+    EXPECT_CALL(mmu, read_byte(registers.pc + 1u)).WillOnce(Return(0xAD));
+    EXPECT_CALL(mmu, write_byte(kStackOffset + registers.sp, 0x12));
+    EXPECT_CALL(mmu, write_byte(kStackOffset + registers.sp - 1u, 0x36));
+    EXPECT_CALL(mmu, read_byte(registers.pc + 2u)).WillOnce(Return(0xDE));
 
     step_execution(6);
     EXPECT_EQ(expected, registers);