From a6907044bd8571c7cecf53f0b358e2305653871a Mon Sep 17 00:00:00 2001
From: scawful <justin.scofield@outlook.com>
Date: Sat, 11 May 2024 13:56:19 -0400
Subject: [PATCH] add experimental single-cycle step control to spc700

---
 src/app/emu/audio/internal/instructions.cc | 18 ++++++++----
 src/app/emu/audio/spc700.cc                | 31 +++++++++++++++-----
 src/app/emu/audio/spc700.h                 | 33 ++++++++++++++--------
 3 files changed, 57 insertions(+), 25 deletions(-)

diff --git a/src/app/emu/audio/internal/instructions.cc b/src/app/emu/audio/internal/instructions.cc
index 13f19e03..ee207e9e 100644
--- a/src/app/emu/audio/internal/instructions.cc
+++ b/src/app/emu/audio/internal/instructions.cc
@@ -20,18 +20,24 @@ void Spc700::MOVY(uint16_t adr) {
 }
 
 void Spc700::MOVS(uint16_t adr) {
-  read(adr);
-  write(adr, A);
+  switch (bstep) {
+    case 0: read(adr); break;
+    case 1: write(adr, A); bstep = 0; break;
+  }
 }
 
 void Spc700::MOVSX(uint16_t adr) {
-  read(adr);
-  write(adr, X);
+  switch (bstep) {
+    case 0: read(adr); break;
+    case 1: write(adr, X); bstep = 0; break;
+  }
 }
 
 void Spc700::MOVSY(uint16_t adr) {
-  read(adr);
-  write(adr, Y);
+  switch (bstep) {
+    case 0: read(adr); break;
+    case 1: write(adr, Y); bstep = 0; break;
+  }
 }
 
 void Spc700::MOV(uint16_t adr) {
diff --git a/src/app/emu/audio/spc700.cc b/src/app/emu/audio/spc700.cc
index de970118..1c5dee06 100644
--- a/src/app/emu/audio/spc700.cc
+++ b/src/app/emu/audio/spc700.cc
@@ -22,6 +22,7 @@ void Spc700::Reset(bool hard) {
     SP = 0x00;
     PSW = ByteToFlags(0x00);
   }
+  step = 0;
   stopped_ = false;
   reset_wanted_ = true;
 }
@@ -44,7 +45,14 @@ void Spc700::RunOpcode() {
     callbacks_.idle(true);
     return;
   }
-  ExecuteInstructions(ReadOpcode());
+  if (step == 0) {
+    bstep = 0;
+    opcode = ReadOpcode();
+    step = 1;
+    return;
+  }
+  ExecuteInstructions(opcode);
+  if (step == 1) step = 0;  // reset step for non cycle-stepped opcodes.
 }
 
 void Spc700::ExecuteInstructions(uint8_t opcode) {
@@ -814,7 +822,6 @@ void Spc700::ExecuteInstructions(uint8_t opcode) {
       A--;
       PSW.Z = (A == 0);
       PSW.N = (A & 0x80);
-      ;
       break;
     }
     case 0x9d: {  // movxp imp
@@ -843,7 +850,6 @@ void Spc700::ExecuteInstructions(uint8_t opcode) {
       A = yva & 0xff;
       PSW.Z = (A == 0);
       PSW.N = (A & 0x80);
-      ;
       break;
     }
     case 0x9f: {  // xcn imp
@@ -991,7 +997,6 @@ void Spc700::ExecuteInstructions(uint8_t opcode) {
       }
       PSW.Z = (A == 0);
       PSW.N = (A & 0x80);
-      ;
       break;
     }
     case 0xbf: {  // mov ind+
@@ -1069,7 +1074,21 @@ void Spc700::ExecuteInstructions(uint8_t opcode) {
       break;
     }
     case 0xd0: {  // bne rel
-      DoBranch(ReadOpcode(), !PSW.Z);
+      switch (step++) {
+        case 1:
+          dat = ReadOpcode();
+          if (PSW.Z) step = 0;
+          break;
+        case 2:
+          callbacks_.idle(false);
+          break;
+        case 3:
+          callbacks_.idle(false);
+          PC += (int8_t)dat;
+          step = 0;
+          break;
+      }
+      // DoBranch(ReadOpcode(), !PSW.Z);
       break;
     }
     case 0xd4: {  // movs dpx
@@ -1276,8 +1295,6 @@ void Spc700::ExecuteInstructions(uint8_t opcode) {
       throw std::runtime_error("Unknown SPC opcode: " + std::to_string(opcode));
       break;
   }
-
-  //LogInstruction(initialPC, opcode);
 }
 
 void Spc700::LogInstruction(uint16_t initial_pc, uint8_t opcode) {
diff --git a/src/app/emu/audio/spc700.h b/src/app/emu/audio/spc700.h
index cb9b02ac..07128599 100644
--- a/src/app/emu/audio/spc700.h
+++ b/src/app/emu/audio/spc700.h
@@ -76,6 +76,15 @@ class Spc700 {
 
   bool stopped_;
   bool reset_wanted_;
+  // single-cycle
+  uint8_t opcode;
+  uint32_t step = 0;
+  uint32_t bstep;
+  uint16_t adr;
+  uint16_t adr1;
+  uint8_t dat;
+  uint16_t dat16;
+  uint8_t param;
 
   const uint8_t ipl_rom_[64]{
       0xCD, 0xEF, 0xBD, 0xE8, 0x00, 0xC6, 0x1D, 0xD0, 0xFC, 0x8F, 0xAA,
@@ -97,14 +106,14 @@ class Spc700 {
   uint8_t SP = 0x00;     // stack pointer
 
   struct Flags {
-    uint8_t N : 1;  // Negative flag
-    uint8_t V : 1;  // Overflow flag
-    uint8_t P : 1;  // Direct page flag
-    uint8_t B : 1;  // Break flag
-    uint8_t H : 1;  // Half-carry flag
-    uint8_t I : 1;  // Interrupt enable
-    uint8_t Z : 1;  // Zero flag
-    uint8_t C : 1;  // Carry flag
+    bool N : 1;  // Negative flag
+    bool V : 1;  // Overflow flag
+    bool P : 1;  // Direct page flag
+    bool B : 1;  // Break flag
+    bool H : 1;  // Half-carry flag
+    bool I : 1;  // Interrupt enable
+    bool Z : 1;  // Zero flag
+    bool C : 1;  // Carry flag
   };
   Flags PSW;  // Processor status word
 
@@ -139,12 +148,12 @@ class Spc700 {
   uint16_t read_word(uint16_t address) {
     uint8_t adrl = address;
     uint8_t adrh = address + 1;
-    uint8_t value = read(adrl);
-    return value | (read(adrh) << 8);
+    uint8_t value = callbacks_.read(adrl);
+    return value | (callbacks_.read(adrh) << 8);
   }
 
   uint8_t ReadOpcode() {
-    uint8_t opcode = read(PC++);
+    uint8_t opcode = callbacks_.read(PC++);
     return opcode;
   }
 
@@ -169,7 +178,7 @@ class Spc700 {
   }
 
   void push_byte(uint8_t value) {
-    write(0x100 | SP, value);
+    callbacks_.write(0x100 | SP, value);
     SP--;
   }