From ee4907949b3ab3581214fa9f43ec7ec4155fc3ee Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sun, 21 Aug 2016 22:33:57 +0300
Subject: [PATCH] Support for RTC latching. Fixes #4.

---
 Core/gb.c     |  6 +++---
 Core/gb.h     | 15 ++++++++-------
 Core/memory.c | 14 +++++++++-----
 Core/timing.c | 22 +++++++++++-----------
 4 files changed, 31 insertions(+), 26 deletions(-)

diff --git a/Core/gb.c b/Core/gb.c
index 8e83532..76ccf87 100755
--- a/Core/gb.c
+++ b/Core/gb.c
@@ -369,7 +369,7 @@ int GB_save_battery(GB_gameboy_t *gb, const char *path)
         return EIO;
     }
     if (gb->cartridge_type->has_rtc) {
-        if (fwrite(gb->rtc_data, 1, sizeof(gb->rtc_data), f) != sizeof(gb->rtc_data)) {
+        if (fwrite(&gb->rtc_real, 1, sizeof(gb->rtc_real), f) != sizeof(gb->rtc_real)) {
             fclose(f);
             return EIO;
         }
@@ -397,7 +397,7 @@ void GB_load_battery(GB_gameboy_t *gb, const char *path)
         goto reset_rtc;
     }
 
-    if (fread(gb->rtc_data, 1, sizeof(gb->rtc_data), f) != sizeof(gb->rtc_data)) {
+    if (fread(&gb->rtc_real, 1, sizeof(gb->rtc_real), f) != sizeof(gb->rtc_real)) {
         goto reset_rtc;
     }
 
@@ -418,7 +418,7 @@ void GB_load_battery(GB_gameboy_t *gb, const char *path)
     goto exit;
 reset_rtc:
     gb->last_rtc_second = time(NULL);
-    gb->rtc_high |= 0x80; /* This gives the game a hint that the clock should be reset. */
+    gb->rtc_real.high |= 0x80; /* This gives the game a hint that the clock should be reset. */
 exit:
     fclose(f);
     return;
diff --git a/Core/gb.h b/Core/gb.h
index 4c3fe93..18a78ab 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -306,15 +306,16 @@ typedef struct GB_gameboy_s {
     GB_SECTION(rtc,
         union {
             struct {
-                uint8_t rtc_seconds;
-                uint8_t rtc_minutes;
-                uint8_t rtc_hours;
-                uint8_t rtc_days;
-                uint8_t rtc_high;
+                uint8_t seconds;
+                uint8_t minutes;
+                uint8_t hours;
+                uint8_t days;
+                uint8_t high;
             };
-            uint8_t rtc_data[5];
-        };
+            uint8_t data[5];
+        } rtc_real, rtc_latched;
         time_t last_rtc_second;
+        bool rtc_latch;
     );
 
     /* Video Display */
diff --git a/Core/memory.c b/Core/memory.c
index 77dbfb4..d8719c8 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -78,8 +78,8 @@ static uint8_t read_mbc_ram(GB_gameboy_t *gb, uint16_t addr)
     
     if (gb->cartridge_type->has_rtc && gb->mbc_ram_bank >= 8 && gb->mbc_ram_bank <= 0xC) {
         /* RTC read */
-        gb->rtc_high |= ~0xC1; /* Not all bytes in RTC high are used. */
-        return gb->rtc_data[gb->mbc_ram_bank - 8];
+        gb->rtc_latched.high |= ~0xC1; /* Not all bytes in RTC high are used. */
+        return gb->rtc_latched.data[gb->mbc_ram_bank - 8];
     }
 
     if (!gb->mbc_ram) {
@@ -284,7 +284,12 @@ static void write_mbc(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                 case 0x0000: case 0x1000: gb->mbc_ram_enable = (value & 0xF) == 0xA; break;
                 case 0x2000: case 0x3000: gb->mbc3.rom_bank  = value; break;
                 case 0x4000: case 0x5000: gb->mbc3.ram_bank  = value; break;
-                case 0x6000: case 0x7000: /* Todo: Clock latching support */ break;
+                case 0x6000: case 0x7000:
+                    if (!gb->rtc_latch && (value & 1)) { /* Todo: verify condition is correct*/
+                        memcpy(&gb->rtc_latched, &gb->rtc_real, sizeof(gb->rtc_real));
+                    }
+                    gb->rtc_latch = value & 1;
+                    break;
             }
             break;
         case GB_MBC5:
@@ -314,8 +319,7 @@ static void write_mbc_ram(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
 
     if (gb->cartridge_type->has_rtc && gb->mbc_ram_bank >= 8 && gb->mbc_ram_bank <= 0xC) {
         /* RTC read */
-        gb->rtc_data[gb->mbc_ram_bank - 8] = value;
-        gb->rtc_high |= ~0xC1; /* Not all bytes in RTC high are used. */
+        gb->rtc_latched.data[gb->mbc_ram_bank - 8] = gb->rtc_real.data[gb->mbc_ram_bank - 8] = value; /* Todo: does it really write both? */
     }
 
     if (gb->cartridge_type->mbc_type == GB_MBC2) {
diff --git a/Core/timing.c b/Core/timing.c
index 48f28dc..24f7da7 100644
--- a/Core/timing.c
+++ b/Core/timing.c
@@ -114,26 +114,26 @@ void GB_emulate_timer_glitch(GB_gameboy_t *gb, uint8_t old_tac, uint8_t new_tac)
 
 void GB_rtc_run(GB_gameboy_t *gb)
 {
-    if ((gb->rtc_high & 0x40) == 0) { /* is timer running? */
+    if ((gb->rtc_real.high & 0x40) == 0) { /* is timer running? */
         time_t current_time = time(NULL);
         while (gb->last_rtc_second < current_time) {
             gb->last_rtc_second++;
-            if (++gb->rtc_seconds == 60)
+            if (++gb->rtc_real.seconds == 60)
             {
-                gb->rtc_seconds = 0;
-                if (++gb->rtc_minutes == 60)
+                gb->rtc_real.seconds = 0;
+                if (++gb->rtc_real.minutes == 60)
                 {
-                    gb->rtc_minutes = 0;
-                    if (++gb->rtc_hours == 24)
+                    gb->rtc_real.minutes = 0;
+                    if (++gb->rtc_real.hours == 24)
                     {
-                        gb->rtc_hours = 0;
-                        if (++gb->rtc_days == 0)
+                        gb->rtc_real.hours = 0;
+                        if (++gb->rtc_real.days == 0)
                         {
-                            if (gb->rtc_high & 1) /* Bit 8 of days*/
+                            if (gb->rtc_real.high & 1) /* Bit 8 of days*/
                             {
-                                gb->rtc_high |= 0x80; /* Overflow bit */
+                                gb->rtc_real.high |= 0x80; /* Overflow bit */
                             }
-                            gb->rtc_high ^= 1;
+                            gb->rtc_real.high ^= 1;
                         }
                     }
                 }