git.y1.nz

commit bd6843444f7e3cf3d67a312a93110af8fea9148e
parent 29d69600759931360b91d5999b93273431f5c165
Author: Lior Halphon <LIJI32@gmail.com>
Date:   Sun,  1 Jan 2023 22:59:16 +0200

Emulate cart open bus behavior. Fixes #516

Diffstat:
M
Core/gb.h
1
+
M
Core/memory.c
14
++++++++++----

2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/Core/gb.h b/Core/gb.h
@@ -435,6 +435,7 @@ struct GB_gameboy_internal_s {
        int32_t ir_sensor;
        bool effective_ir_input;
        uint16_t address_bus;
+       uint8_t data_bus; // cart data bus
     )
 
     /* DMA and HDMA */
diff --git a/Core/memory.c b/Core/memory.c
@@ -379,14 +379,14 @@ static uint8_t read_mbc_ram(GB_gameboy_t *gb, uint16_t addr)
             case 5:
                 return gb->rtc_latched.data[(addr & 3) ^ 3];
             default:
-                return 0xFF;
+                return gb->data_bus;
         }
     }
     else if ((!gb->mbc_ram_enable) &&
         gb->cartridge_type->mbc_type != GB_CAMERA &&
         gb->cartridge_type->mbc_type != GB_HUC1 &&
         gb->cartridge_type->mbc_type != GB_HUC3) {
-        return 0xFF;
+        return gb->data_bus;
     }
     
     if (gb->cartridge_type->mbc_type == GB_HUC1 && gb->huc1.ir_mode) {
@@ -403,7 +403,7 @@ static uint8_t read_mbc_ram(GB_gameboy_t *gb, uint16_t addr)
             gb->rtc_latched.high &= 0xC1;
             return gb->rtc_latched.data[gb->mbc_ram_bank];
         }
-        return 0xFF;
+        return gb->data_bus;
     }
 
     if (gb->camera_registers_mapped) {
@@ -411,7 +411,7 @@ static uint8_t read_mbc_ram(GB_gameboy_t *gb, uint16_t addr)
     }
 
     if (!gb->mbc_ram || !gb->mbc_ram_size) {
-        return 0xFF;
+        return gb->data_bus;
     }
 
     if (gb->cartridge_type->mbc_type == GB_CAMERA) {
@@ -777,6 +777,12 @@ uint8_t GB_read_memory(GB_gameboy_t *gb, uint16_t addr)
     if (unlikely(gb->read_memory_callback)) {
         data = gb->read_memory_callback(gb, addr, data);
     }
+    if ((addr & 0xE000) != 0xA000 && bus_for_addr(gb, addr) == GB_BUS_MAIN && addr < 0xFF00) {
+        gb->data_bus = data;
+    }
+    else {
+        gb->data_bus = 0xFF;
+    }
     return data;
 }
 

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