More accurate emulation of STOP

Core/gb.h

@@ -297,7 +297,6 @@ typedef enum {
 #define SGB_NTSC_FREQUENCY (21477272 / 5)
 #define SGB_PAL_FREQUENCY (21281370 / 5)
 #define DIV_CYCLES (0x100)
-#define INTERNAL_DIV_CYCLES (0x40000)
 
 #if !defined(MIN)
 #define MIN(A, B)    ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a < __b ? __a : __b; })
@@ -532,6 +531,8 @@ struct GB_gameboy_internal_s {
         uint16_t serial_length;
         uint8_t double_speed_alignment;
         uint8_t serial_count;
+        int32_t speed_switch_halt_countdown;
+        uint8_t speed_switch_freeze; // Solely for realigning the PPU, should be removed when the odd modes are implemented
     );
 
     /* APU */

Core/sm83_cpu.c

@@ -357,6 +357,9 @@ static void nop(GB_gameboy_t *gb, uint8_t opcode)
 static void enter_stop_mode(GB_gameboy_t *gb)
 {
     GB_write_memory(gb, 0xFF00 + GB_IO_DIV, 0);
+    if (!gb->ime) { // TODO: I don't trust this if,
+        gb->div_cycles = -4; // Emulate the CPU-side DIV-reset signal being held
+    }
     gb->stopped = true;
     gb->oam_ppu_blocked = !gb->oam_read_blocked;
     gb->vram_ppu_blocked = !gb->vram_read_blocked;
@@ -369,53 +372,56 @@ static void leave_stop_mode(GB_gameboy_t *gb)
     gb->oam_ppu_blocked = false;
     gb->vram_ppu_blocked = false;
     gb->cgb_palettes_ppu_blocked = false;
-    /* The CPU takes more time to wake up then the other components */
-    for (unsigned i = 0x1FFF; i--;) {
-        GB_advance_cycles(gb, 0x10);
-    }
-    GB_advance_cycles(gb, gb->cgb_double_speed? 0x10 : 0xC);
-    GB_write_memory(gb, 0xFF00 + GB_IO_DIV, 0);
 }
 
 static void stop(GB_gameboy_t *gb, uint8_t opcode)
 {
-    if (gb->io_registers[GB_IO_KEY1] & 0x1) {
     flush_pending_cycles(gb);
-        bool needs_alignment = false;
+    bool exit_by_joyp = ((gb->io_registers[GB_IO_JOYP] & 0xF) != 0xF);
+    bool speed_switch = (gb->io_registers[GB_IO_KEY1] & 0x1) && !exit_by_joyp;
+    bool immediate_exit = speed_switch || exit_by_joyp;
+    bool interrupt_pending = (gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F);
+    // When entering with IF&IE, the 2nd byte of STOP is actually executed
+    if (!exit_by_joyp) {
+        enter_stop_mode(gb);
+    }
     
-        GB_advance_cycles(gb, 0x4);
+    if (!interrupt_pending) {
-        /* Make sure we keep the CPU ticks aligned correctly when returning from double speed mode */
+        /* Todo: is PC being actually read? */
+        cycle_read_inc_oam_bug(gb, gb->pc++);
+    }
     
-        if (gb->double_speed_alignment & 7) {
+    /* Todo: speed switching takes a fractional number of M-cycles. It make
-            GB_advance_cycles(gb, 0x4);
+             every active component (APU, PPU) unaligned with the CPU. */
-            needs_alignment = true;
+    if (speed_switch) {
+        flush_pending_cycles(gb);
+        
+        if (gb->io_registers[GB_IO_LCDC] & 0x80) {
             GB_log(gb, "ROM triggered PPU odd mode, which is currently not supported. Reverting to even-mode.\n");
+            if (gb->double_speed_alignment & 7) {
+                gb->speed_switch_freeze = 6;
+            }
+            else {
+                gb->speed_switch_freeze = 4;
+            }
         }
         
         gb->cgb_double_speed ^= true;
         gb->io_registers[GB_IO_KEY1] = 0;
         
-        enter_stop_mode(gb);
+        gb->speed_switch_halt_countdown = 0x20008;
+    }
+    
+    if (immediate_exit) {
         leave_stop_mode(gb);
-        
+        if (!interrupt_pending) {
-        if (!needs_alignment) {
-            GB_advance_cycles(gb, 0x4);
-        }
-        
-    }
-    else {
-        GB_timing_sync(gb);
-        if ((gb->io_registers[GB_IO_JOYP] & 0xF) != 0xF) {
-            /* TODO: HW Bug? When STOP is executed while a button is down, the CPU enters halt
-               mode instead. Fine details not confirmed yet. */
             gb->halted = true;
+            gb->just_halted = true;
         }
         else {
-            enter_stop_mode(gb);
+            gb->speed_switch_halt_countdown = 0;
         }
     }
-    /* Todo: is PC being actually read? */
-    gb->pc++;
 }
 
 /* Operand naming conventions for functions:
@@ -1603,11 +1609,13 @@ void GB_cpu_run(GB_gameboy_t *gb)
     /* Wake up from HALT mode without calling interrupt code. */
     if (gb->halted && !effective_ime && interrupt_queue) {
         gb->halted = false;
+        gb->speed_switch_halt_countdown = 0;
     }
     
     /* Call interrupt */
     else if (effective_ime && interrupt_queue) {
         gb->halted = false;
+        gb->speed_switch_halt_countdown = 0;
         uint16_t call_addr = gb->pc;
         
         gb->last_opcode_read = cycle_read_inc_oam_bug(gb, gb->pc++);

Core/timing.c

@@ -145,7 +145,6 @@ static void increase_tima(GB_gameboy_t *gb)
 static void GB_set_internal_div_counter(GB_gameboy_t *gb, uint16_t value)
 {
     /* TIMA increases when a specific high-bit becomes a low-bit. */
-    value &= INTERNAL_DIV_CYCLES - 1;
     uint16_t triggers = gb->div_counter & ~value;
     if ((gb->io_registers[GB_IO_TAC] & 4) && (triggers & GB_TAC_TRIGGER_BITS[gb->io_registers[GB_IO_TAC] & 3])) {
         increase_tima(gb);
@@ -356,8 +355,25 @@ void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles)
         advance_serial(gb, cycles); // TODO: Verify what happens in STOP mode
     }
 
+    if (gb->speed_switch_halt_countdown) {
+        gb->speed_switch_halt_countdown -= cycles;
+        if (gb->speed_switch_halt_countdown <= 0) {
+            gb->speed_switch_halt_countdown = 0;
+            gb->halted = false;
+        }
+    }
+    
     gb->debugger_ticks += cycles;
     
+    if (gb->speed_switch_freeze) {
+        if (gb->speed_switch_freeze >= cycles) {
+            gb->speed_switch_freeze -= cycles;
+            return;
+        }
+        cycles -= gb->speed_switch_freeze;
+        gb->speed_switch_freeze = 0;
+    }
+
     if (!gb->cgb_double_speed) {
         cycles <<= 1;
     }

Tester/main.c

@@ -27,7 +27,7 @@ static FILE *log_file;
 static void replace_extension(const char *src, size_t length, char *dest, const char *ext);
 static bool push_start_a, start_is_not_first, a_is_bad, b_is_confirm, push_faster, push_slower,
             do_not_stop, push_a_twice, start_is_bad, allow_weird_sp_values, large_stack, push_right,
-            semi_random, limit_start, pointer_control;
+            semi_random, limit_start, pointer_control, unsafe_speed_switch;
 static unsigned int test_length = 60 * 40;
 GB_gameboy_t gb;
 
@@ -60,6 +60,9 @@ static char *async_input_callback(GB_gameboy_t *gb)
 
 static void handle_buttons(GB_gameboy_t *gb)
 {
+    if (!gb->cgb_double_speed && unsafe_speed_switch) {
+        return;
+    }
     /* Do not press any buttons during the last two seconds, this might cause a
      screenshot to be taken while the LCD is off if the press makes the game
      load graphics. */
@@ -129,7 +132,7 @@ static void vblank(GB_gameboy_t *gb)
                    gb->registers[GB_REGISTER_SP], gb->backtrace_size);
             frames = test_length - 1;
         }
-        if (gb->halted && !gb->interrupt_enable) {
+        if (gb->halted && !gb->interrupt_enable && gb->speed_switch_halt_countdown == 0) {
             GB_log(gb, "The game is deadlocked.\n");
             frames = test_length - 1;
         }
@@ -265,9 +268,7 @@ static void replace_extension(const char *src, size_t length, char *dest, const
 
 int main(int argc, char **argv)
 {
-#define str(x) #x
+    fprintf(stderr, "SameBoy Tester v" GB_VERSION "\n");
-#define xstr(x) str(x)
-    fprintf(stderr, "SameBoy Tester v" xstr(VERSION) "\n");
 
     if (argc == 1) {
         fprintf(stderr, "Usage: %s [--dmg] [--start] [--length seconds] [--sav] [--boot path to boot ROM]"
@@ -406,7 +407,8 @@ int main(int argc, char **argv)
                        strcmp((const char *)(gb.rom + 0x134), "ONI 5") == 0;
         b_is_confirm = strcmp((const char *)(gb.rom + 0x134), "ELITE SOCCER") == 0 ||
                        strcmp((const char *)(gb.rom + 0x134), "SOCCER") == 0 ||
-                       strcmp((const char *)(gb.rom + 0x134), "GEX GECKO") == 0;
+                       strcmp((const char *)(gb.rom + 0x134), "GEX GECKO") == 0 ||
+                       strcmp((const char *)(gb.rom + 0x134), "BABE") == 0;
         push_faster = strcmp((const char *)(gb.rom + 0x134), "MOGURA DE PON!") == 0 ||
                       strcmp((const char *)(gb.rom + 0x134), "HUGO2 1/2") == 0 ||
                       strcmp((const char *)(gb.rom + 0x134), "HUGO") == 0;
@@ -445,6 +447,11 @@ int main(int argc, char **argv)
         pointer_control = memcmp((const char *)(gb.rom + 0x134), "LEGO ATEAM BLPP", strlen("LEGO ATEAM BLPP")) == 0;
         push_faster |= pointer_control;
         
+        /* Games that perform an unsafe speed switch, don't input until in double speed */
+        unsafe_speed_switch = strcmp((const char *)(gb.rom + 0x134), "GBVideo") == 0 || // lulz this is my fault
+                              strcmp((const char *)(gb.rom + 0x134), "POKEMONGOLD 2") == 0; // Pokemon Adventure
+
+        
         /* Run emulation */
         running = true;
         gb.turbo = gb.turbo_dont_skip = gb.disable_rendering = true;