git.y1.nz

commit 88e64fadda5314debe88f67121d4c32ee3ef2cb4
parent c92a2c21314549a90268314991bc31d6790ac9e6
Author: Lior Halphon <LIJI32@gmail.com>
Date:   Fri,  6 Jan 2023 19:06:22 +0200

More accurate and customizable timings

Diffstat:
M
Core/gb.c
7
+++++++
M
Core/gb.h
13
+++++++++----
M
Core/memory.c
13
+++++--------
M
Core/timing.c
12
+++++++++++-

4 files changed, 32 insertions(+), 13 deletions(-)
diff --git a/Core/gb.c b/Core/gb.c
@@ -183,6 +183,8 @@ GB_gameboy_t *GB_init(GB_gameboy_t *gb, GB_model_t model)
         gb->turbo = true;
     }
     
+    gb->data_bus_decay = 12;
+    
     GB_reset(gb);
     load_default_border(gb);
     return gb;
@@ -1991,6 +1993,11 @@ void GB_set_accelerometer_values(GB_gameboy_t *gb, double x, double y)
     gb->accelerometer_y = y;
 }
 
+void GB_set_open_bus_decay_time(GB_gameboy_t *gb, uint32_t decay)
+{
+    gb->data_bus_decay = decay;
+}
+
 void GB_get_rom_title(GB_gameboy_t *gb, char *title)
 {
     memset(title, 0, 17);
diff --git a/Core/gb.h b/Core/gb.h
@@ -432,10 +432,11 @@ struct GB_gameboy_internal_s {
         uint32_t ram_size; // Different between CGB and DMG
         GB_workboy_t workboy;
                
-       int32_t ir_sensor;
-       bool effective_ir_input;
-       uint16_t address_bus;
-       uint8_t data_bus; // cart data bus
+        int32_t ir_sensor;
+        bool effective_ir_input;
+        uint16_t address_bus;
+        uint8_t data_bus; // cart data bus (MAIN)
+        uint32_t data_bus_decay_countdown;
     )
 
     /* DMA and HDMA */
@@ -719,6 +720,7 @@ struct GB_gameboy_internal_s {
         uint32_t rtc_second_length;
         uint32_t clock_rate;
         uint32_t unmultiplied_clock_rate;
+        uint32_t data_bus_decay;
 
         /* Audio */
         GB_apu_output_t apu_output;
@@ -979,6 +981,9 @@ bool GB_has_accelerometer(GB_gameboy_t *gb);
 // Values within ±4 recommended
 void GB_set_accelerometer_values(GB_gameboy_t *gb, double x, double y);
     
+// Time it takes for a value in the data bus to decay to FF, in 8MHz units. (0 to never decay, like e.g. an EverDrive)
+void GB_set_open_bus_decay_time(GB_gameboy_t *gb, uint32_t decay);
+    
 /* For integration with SFC/SNES emulators */
 void GB_set_joyp_write_callback(GB_gameboy_t *gb, GB_joyp_write_callback_t callback);
 void GB_set_icd_pixel_callback(GB_gameboy_t *gb, GB_icd_pixel_callback_t callback);
diff --git a/Core/memory.c b/Core/memory.c
@@ -786,16 +786,13 @@ uint8_t GB_read_memory(GB_gameboy_t *gb, uint16_t addr)
              but should be good enough */
     if (bus_for_addr(gb, addr) == GB_BUS_MAIN && addr < 0xFF00) {
         if (unlikely(gb->returned_open_bus)) {
-            gb->data_bus = 0xFF;
             gb->returned_open_bus = false;
         }
         else {
             gb->data_bus = data;
+            gb->data_bus_decay_countdown = gb->data_bus_decay;
         }
     }
-    else {
-        gb->data_bus = 0xFF;
-    }
     return data;
 }
 
@@ -1738,9 +1735,7 @@ void GB_write_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
     }
     if (bus_for_addr(gb, addr) == GB_BUS_MAIN && addr < 0xFF00) {
         gb->data_bus = value;
-    }
-    else {
-        gb->data_bus = 0xFF;
+        gb->data_bus_decay_countdown = gb->data_bus_decay;
     }
     
     if (unlikely(gb->write_memory_callback)) {
@@ -1831,10 +1826,13 @@ void GB_dma_run(GB_gameboy_t *gb)
 void GB_hdma_run(GB_gameboy_t *gb)
 {
     unsigned cycles = gb->cgb_double_speed? 4 : 2;
+    /* TODO: This portion of code is probably inaccurate because it probably depends on my specific GB-Live32 */
+    #if 0
     /* This is a bit cart, revision and unit specific. TODO: what if PC is in cart RAM? */
     if (gb->model < GB_MODEL_CGB_D || gb->pc > 0x8000) {
         gb->data_bus = 0xFF;
     }
+    #endif
     gb->addr_for_hdma_conflict = 0xFFFF;
     uint16_t vram_base = gb->cgb_vram_bank? 0x2000 : 0;
     gb->hdma_in_progress = true;
@@ -1877,7 +1875,6 @@ void GB_hdma_run(GB_gameboy_t *gb)
             }
             gb->hdma_current_dest++;
         }
-        gb->data_bus = 0xFF;
         
         if ((gb->hdma_current_dest & 0xF) == 0) {
             if (--gb->hdma_steps_left == 0 || gb->hdma_current_dest == 0) {
diff --git a/Core/timing.c b/Core/timing.c
@@ -421,7 +421,7 @@ void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles)
             gb->halted = false;
         }
     }
-    
+        
     gb->debugger_ticks += cycles;
     
     if (gb->speed_switch_freeze) {
@@ -450,6 +450,16 @@ void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles)
     gb->rumble_on_cycles += gb->rumble_strength & 3;
     gb->rumble_off_cycles += (gb->rumble_strength & 3) ^ 3;
     
+    if (unlikely(gb->data_bus_decay_countdown)) {
+        if (gb->data_bus_decay_countdown <= cycles) {
+            gb->data_bus_decay_countdown = 0;
+            gb->data_bus = 0xFF;
+        }
+        else {
+            gb->data_bus_decay_countdown -= cycles;
+        }
+    }
+    
     GB_joypad_run(gb, cycles);
     GB_apu_run(gb, false);
     GB_display_run(gb, cycles, false);

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