From 4baad291dcd98d8d392541b578a66ab1cc941c04 Mon Sep 17 00:00:00 2001
From: zeromus <zeromus@users.sf.net>
Date: Sat, 31 Aug 2013 18:51:09 +0000
Subject: [PATCH] clarify chipId checks and fake booting

---
 desmume/src/NDSSystem.cpp                 | 20 +++++++++-----------
 desmume/src/addons/slot1comp_protocol.cpp | 10 +++-------
 2 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/desmume/src/NDSSystem.cpp b/desmume/src/NDSSystem.cpp
index d2adcfa4c..93717369f 100644
--- a/desmume/src/NDSSystem.cpp
+++ b/desmume/src/NDSSystem.cpp
@@ -2647,7 +2647,7 @@ void NDS_Reset()
 				_MMU_write08<ARMCPU_ARM9>(0x027FFC80 + fw_index, temp_buffer[fw_index]);
 		}
 
-		//firmware copies the whole header to Main RAM 0x27FFE00 on startup. (http://nocash.emubase.de/gbatek.htm#dscartridgeheader)
+		//something copies the whole header to Main RAM 0x27FFE00 on startup. (http://nocash.emubase.de/gbatek.htm#dscartridgeheader)
 		//once upon a time this copied 0x90 more. this was thought to be wrong, and changed.
 		if(nds.Is_DSI())
 		{
@@ -2669,20 +2669,18 @@ void NDS_Reset()
 		MMU.ARM9_REG[0x300] = 1;
 		MMU.ARM7_REG[0x300] = 1;
 
-		//firmware makes system think it's booted from card -- EXTREMELY IMPORTANT!!! Thanks to cReDiAr
-		_MMU_write08<ARMCPU_ARM9>(0x02FFFC40,0x1);
-		_MMU_write08<ARMCPU_ARM7>(0x02FFFC40,0x1);
+		//firmware makes system think it's booted from card -- EXTREMELY IMPORTANT!!! This is actually checked by some things. (which things?) Thanks to cReDiAr
+		_MMU_write08<ARMCPU_ARM7>(0x02FFFC40,0x1); //<zero> removed redundant write to ARM9, this is going to shared main memory. But one has to wonder why r3478 was made which corrected a typo resulting in only ARMCPU_ARM7 getting used.
 
-		//
-		_MMU_write32<ARMCPU_ARM7>(0x027FF800, gameInfo.chipID);		// Chip ID
-		_MMU_write32<ARMCPU_ARM7>(0x027FF804, gameInfo.chipID);		// Secure Chip ID
-		_MMU_write32<ARMCPU_ARM7>(0x027FFC00, gameInfo.chipID);		// 2nd Secure Chip ID
+		//the chipId is read several times
+		//for some reason, each of those reads get stored here.
+		_MMU_write32<ARMCPU_ARM7>(0x027FF800, gameInfo.chipID);		//1st chipId
+		_MMU_write32<ARMCPU_ARM7>(0x027FF804, gameInfo.chipID);		//2nd (secure) chipId
+		_MMU_write32<ARMCPU_ARM7>(0x027FFC00, gameInfo.chipID);		//3rd (secure) chipId
+		
 		// Write the header checksum to memory
 		_MMU_write16<ARMCPU_ARM9>(0x027FF808, gameInfo.header.headerCRC16);
 
-		// Write the header checksum to memory (the firmware needs it to see the cart)
-		//_MMU_write16<ARMCPU_ARM9>(0x027FF808, T1ReadWord(MMU.CART_ROM, 0x15E));
-
 		// Save touchscreen calibration info in a structure
 		// so we can easily access it at any time
 		// TODO - this isn't good. need revising.
diff --git a/desmume/src/addons/slot1comp_protocol.cpp b/desmume/src/addons/slot1comp_protocol.cpp
index 8dfa82040..2363e2c8d 100644
--- a/desmume/src/addons/slot1comp_protocol.cpp
+++ b/desmume/src/addons/slot1comp_protocol.cpp
@@ -209,13 +209,9 @@ u32 Slot1Comp_Protocol::read_GCDATAIN(u8 PROCNUM)
 
 		case eSlot1Operation_90_ChipID:
 		case eSlot1Operation_B8_ChipID:
-			// Note: the BIOS stores the chip ID in main memory
-			// Most games continuously compare the chip ID with
-			// the value in memory, probably to know if the card
-			// was removed.
-			// As DeSmuME normally boots directly from the game, the chip
-			// ID in main mem is zero and this value needs to be
-			// zero too.
+			
+			//Most games continuously compare the current chipId with the value in 
+			//stored in memory at boot-up, probably to know if the card was removed.
 
 			//staff of kings verifies this (it also uses the arm7 IRQ 20 to detect card ejects)
 			return chipId;