Use correct timing in absolute addressing pipeline

evilcorpltd · Sep 15, 2019 · 924fc7f · 924fc7f
1 parent d1e4b0a
commit 924fc7f
Show file tree

Hide file tree

Showing 2 changed files with 20 additions and 6 deletions.
diff --git a/core/src/mos6502.cpp b/core/src/mos6502.cpp
@@ -629,10 +629,14 @@ Pipeline Mos6502::create_zeropage_indexed_addressing_steps(
 
 Pipeline Mos6502::create_absolute_addressing_steps() {
     Pipeline result;
-    result.push([=]() { ++registers_->pc; });
     result.push([=]() {
+        tmp_ = mmu_->read_byte(registers_->pc);
+        ++registers_->pc;
+    });
+    result.push([=]() {
+        const uint16_t upper = mmu_->read_byte(registers_->pc) << 8;
         ++registers_->pc;
-        effective_address_ = mmu_->read_word(registers_->pc - 2);
+        effective_address_ = tmp_ | upper;
     });
     return result;
 }

diff --git a/core/test/src/test_cpu.cpp b/core/test/src/test_cpu.cpp
@@ -510,8 +510,13 @@ class CpuAbsoluteTest : public CpuTest {
         stage_instruction(instruction);
         expected.pc += 2;
 
-        EXPECT_CALL(mmu, read_word(start_pc + 1))
-                .WillOnce(Return(effective_address));
+        const uint8_t lower_address = effective_address & 0x00FF;
+        const uint8_t upper_address = (effective_address & 0xFF00) >> 8;
+
+        EXPECT_CALL(mmu, read_byte(start_pc + 1))
+                .WillOnce(Return(lower_address));
+        EXPECT_CALL(mmu, read_byte(start_pc + 2))
+                .WillOnce(Return(upper_address));
         EXPECT_CALL(mmu, read_byte(effective_address))
                 .WillOnce(Return(memory_content));
 
@@ -524,8 +529,13 @@ class CpuAbsoluteTest : public CpuTest {
         stage_instruction(instruction);
         expected.pc += 2;
 
-        EXPECT_CALL(mmu, read_word(start_pc + 1))
-                .WillOnce(Return(effective_address));
+        const uint8_t lower_address = effective_address & 0x00FF;
+        const uint8_t upper_address = (effective_address & 0xFF00) >> 8;
+
+        EXPECT_CALL(mmu, read_byte(start_pc + 1))
+                .WillOnce(Return(lower_address));
+        EXPECT_CALL(mmu, read_byte(start_pc + 2))
+                .WillOnce(Return(upper_address));
         EXPECT_CALL(mmu, write_byte(effective_address, memory_content));
 
         step_execution(4);