From 55bf63210ae882ccacbd2888e10ec540cebc6bd0 Mon Sep 17 00:00:00 2001
From: Logan McNaughton <848146+loganmc10@users.noreply.github.com>
Date: Sat, 9 May 2026 15:12:20 +0200
Subject: [PATCH] Don't save timestamp to GB save (#860)

* use real time for GB RTC

* more

* more

* more
---
 src/device/controller/gbcart.rs | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/src/device/controller/gbcart.rs b/src/device/controller/gbcart.rs
index 593fc1e..a22424c 100644
--- a/src/device/controller/gbcart.rs
+++ b/src/device/controller/gbcart.rs
@@ -22,8 +22,7 @@ pub struct GbCart {
     pub latch: bool,
     pub rtc_regs: [u8; MBC3_RTC_REGS_COUNT],
     pub rtc_regs_latch: [u8; MBC3_RTC_REGS_COUNT],
-    pub rtc_timestamp: i64,
-    pub last_time: i64,
+    pub last_elapsed_time: i64,
 }
 
 #[derive(Default, Copy, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
@@ -43,14 +42,10 @@ pub fn init(gb_cart: &mut device::controller::gbcart::GbCart, rom: &[u8], ram: &
         44 => {
             offset = ram.len() - 44;
             gb_cart.ram = ram[..ram.len() - 44].to_vec();
-            gb_cart.rtc_timestamp =
-                i32::from_le_bytes(ram[offset + 40..offset + 44].try_into().unwrap()) as i64;
         }
         48 => {
             offset = ram.len() - 48;
             gb_cart.ram = ram[..ram.len() - 48].to_vec();
-            gb_cart.rtc_timestamp =
-                i64::from_le_bytes(ram[offset + 40..offset + 48].try_into().unwrap());
         }
         _ => {
             gb_cart.ram = ram.to_vec();
@@ -115,8 +110,8 @@ pub fn save(
             f.write_all(&(gb_cart.rtc_regs_latch[MBC3_RTC_DAYS_H] as u32).to_le_bytes())
                 .unwrap();
 
-            let timestamp = gb_cart.rtc_timestamp.saturating_add(elapsed_time);
-            f.write_all(&timestamp.to_le_bytes()).unwrap();
+            let max = ((i32::MAX as i64) << 32) | (i32::MAX as i64);
+            f.write_all(&max.to_le_bytes()).unwrap();
 
             f.flush().unwrap();
         }
@@ -126,8 +121,8 @@ pub fn save(
 }
 
 fn update_rtc_regs(cart: &mut device::controller::gbcart::GbCart, elapsed_time: i64) {
-    let mut diff = elapsed_time - cart.last_time;
-    cart.last_time = elapsed_time;
+    let mut diff = elapsed_time - cart.last_elapsed_time;
+    cart.last_elapsed_time = elapsed_time;
 
     if diff > 0 {
         cart.rtc_regs[MBC3_RTC_SECONDS] += (diff % 60) as u8;
@@ -157,8 +152,8 @@ fn update_rtc_regs(cart: &mut device::controller::gbcart::GbCart, elapsed_time:
             + diff;
 
         cart.rtc_regs[MBC3_RTC_DAYS_L] = (days & 0xff) as u8;
-        cart.rtc_regs[MBC3_RTC_DAYS_H] =
-            ((cart.rtc_regs[MBC3_RTC_DAYS_H] & !0x01) as i64 | (days & 0x100)) as u8;
+        cart.rtc_regs[MBC3_RTC_DAYS_H] &= !0x01;
+        cart.rtc_regs[MBC3_RTC_DAYS_H] |= ((days >> 8) & 1) as u8;
 
         /* set carry bit if days overflow */
         if days > 511 {