Implemented a very basic form of GD-ROM Sense. Only disc swap related Sense currently works. Added some very basic disc swap handling on x86/Windows (press "0">Cancel to remove disc, then "0" again and select the new disc).

Notes:
Disc swapping should work on .gdi files (probably .chd files too).
Swapping with .cdi files is not currently supported because we currently create inaccurate TOC for them.
Only x86/Windows has a disc swap handler right now (ie: you can't swap on Android).

core/hw/gdrom/gdromv3.cpp

@@ -19,6 +19,11 @@
 
 int gdrom_schid;
 
+//Sense: ASC - ASCQ - Key
+signed int sns_asc=0;
+signed int sns_ascq=0;
+signed int sns_key=0;
+
 enum gd_states
 {
 	//Generic
@@ -447,7 +452,11 @@ void gd_process_ata_cmd()
 {
 	//Any ATA command clears these bits, unless aborted/error :p
 	Error.ABRT=0;
-	GDStatus.CHECK=0;
+	
+	if (sns_key==0x0 || sns_key==0xB)
+		GDStatus.CHECK=0;
+	else
+		GDStatus.CHECK=1;
 
 	switch(ata_cmd.command)
 	{
@@ -464,7 +473,7 @@ void gd_process_ata_cmd()
 		//the above comment is from a wrong place in the docs ...
 		
 		Error.ABRT=1;
-		//Error.Sense=0x00; //fixme ?
+		Error.Sense=sns_key;
 		GDStatus.BSY=0;
 		GDStatus.CHECK=1;
 
@@ -519,12 +528,18 @@ void gd_process_ata_cmd()
 
 void gd_process_spi_cmd()
 {
+
+	printf_spi("Sense: %02x %02x %02x \n", sns_asc, sns_ascq, sns_key);
+
 	printf_spi("SPI command %02x;",packet_cmd.data_8[0]);
 	printf_spi("Params: %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x \n",
 		packet_cmd.data_8[0], packet_cmd.data_8[1], packet_cmd.data_8[2], packet_cmd.data_8[3], packet_cmd.data_8[4], packet_cmd.data_8[5],
 		packet_cmd.data_8[6], packet_cmd.data_8[7], packet_cmd.data_8[8], packet_cmd.data_8[9], packet_cmd.data_8[10], packet_cmd.data_8[11] );
 
-	GDStatus.CHECK=0;
+	if (sns_key==0x0 || sns_key==0xB)
+		GDStatus.CHECK=0;
+	else
+		GDStatus.CHECK=1;
 
 	switch(packet_cmd.data_8[0])
 	{
@@ -672,18 +687,22 @@ void gd_process_spi_cmd()
 
 	case SPI_REQ_ERROR:
 		printf_spicmd("SPI_REQ_ERROR\n");
-		printf("GDROM: Unhandled Sega SPI frame: SPI_REQ_ERROR\n");
+		//printf("GDROM: Unhandled Sega SPI frame: SPI_REQ_ERROR\n");
 		
 		u8 resp[10];
 		resp[0]=0xF0;
 		resp[1]=0;
-		resp[2]= SecNumber.Status==GD_BUSY ? 2:0;//sense
+		resp[2]=sns_key;//sense
 		resp[3]=0;
 		resp[4]=resp[5]=resp[6]=resp[7]=0; //Command Specific Information
-		resp[8]=0;//Additional Sense Code
+		resp[8]=sns_asc;//Additional Sense Code
-		resp[9]=0;//Additional Sense Code Qualifier
+		resp[9]=sns_ascq;//Additional Sense Code Qualifier
 
 		gd_spi_pio_end(resp,packet_cmd.data_8[4]);
+		sns_key=0;
+		sns_asc=0;
+		sns_ascq=0;
+		//GDStatus.CHECK=0;
 		break;
 
 	case SPI_REQ_SES:
@@ -915,8 +934,8 @@ u32 ReadMem_gdrom(u32 Addr, u32 sz)
 		if(2!=sz)
 			printf("GDROM: Bad size on DATA REG Read\n");
 
-		if (gd_state == gds_pio_send_data)
+		//if (gd_state == gds_pio_send_data)
-		{
+		//{
 			if (pio_buff.index == pio_buff.size)
 			{
 				printf("GDROM: Illegal Read From DATA (underflow)\n");
@@ -935,9 +954,9 @@ u32 ReadMem_gdrom(u32 Addr, u32 sz)
 				return rv;
 			}
 
-		}
+		//}
-		else
+		//else
-			printf("GDROM: Illegal Read From DATA (wrong mode)\n");
+		//	printf("GDROM: Illegal Read From DATA (wrong mode)\n");
 
 		return 0;
 
@@ -947,6 +966,7 @@ u32 ReadMem_gdrom(u32 Addr, u32 sz)
 
 	case GD_ERROR_Read:
 		printf_rm("GDROM: Read from ERROR Register\n");
+		Error.Sense=sns_key;
 		return Error.full;
 
 	case GD_IREASON_Read:

core/imgread/common.cpp

@@ -1,6 +1,5 @@
 #include "common.h"
 
-
 Disc* chd_parse(wchar* file);
 Disc* gdi_parse(wchar* file);
 Disc* cdi_parse(wchar* file);
@@ -169,6 +168,10 @@ bool InitDrive(u32 fileflags)
 	if (gfrv == 0)
 	{
 		NullDriveDiscType=NoDisk;
+		gd_setdisc();
+		sns_asc=0x29;
+		sns_ascq=0x00;
+		sns_key=0x6;
 		return true;
 	}
 	else if (gfrv == -1)
@@ -182,6 +185,11 @@ bool InitDrive(u32 fileflags)
 	if (!InitDrive_(fn))
 	{
 		//msgboxf("Selected image failed to load",MBX_ICONERROR);
+		NullDriveDiscType=NoDisk;
+		gd_setdisc();
+		sns_asc=0x29;
+		sns_ascq=0x00;
+		sns_key=0x6;
 		return true;
 	}
 	else
@@ -190,6 +198,66 @@ bool InitDrive(u32 fileflags)
 	}
 }
 
+bool DiscSwap(u32 fileflags)
+{
+	if (settings.imgread.LoadDefaultImage)
+	{
+		printf("Loading default image \"%s\"\n",settings.imgread.DefaultImage);
+		if (!InitDrive_(settings.imgread.DefaultImage))
+		{
+			msgboxf("Default image \"%s\" failed to load",MBX_ICONERROR);
+			return false;
+		}
+		else
+			return true;
+	}
+
+	wchar fn[512];
+	strcpy(fn,settings.imgread.LastImage);
+#ifdef BUILD_DREAMCAST
+	int gfrv=GetFile(fn,0,fileflags);
+#else
+	int gfrv=0;
+#endif
+	if (gfrv == 0)
+	{
+		NullDriveDiscType=Open;
+		gd_setdisc();
+		sns_asc=0x28;
+		sns_ascq=0x00;
+		sns_key=0x6;
+		return true;
+	}
+	else if (gfrv == -1)
+	{
+		sns_asc=0x28;
+		sns_ascq=0x00;
+		sns_key=0x6;
+		return false;
+	}
+
+	strcpy(settings.imgread.LastImage,fn);
+	SaveSettings();
+
+	if (!InitDrive_(fn))
+	{
+		//msgboxf("Selected image failed to load",MBX_ICONERROR);
+		NullDriveDiscType=Open;
+		gd_setdisc();
+		sns_asc=0x28;
+		sns_ascq=0x00;
+		sns_key=0x6;
+		return true;
+	}
+	else
+	{
+		sns_asc=0x28;
+		sns_ascq=0x00;
+		sns_key=0x6;
+		return true;
+	}
+}
+
 void TermDrive()
 {
 	if (disc!=0)

core/imgread/common.h

@@ -82,6 +82,11 @@ bool ConvertSector(u8* in_buff , u8* out_buff , int from , int to,int sector);
 
 bool InitDrive(u32 fileflags=0);
 void TermDrive();
+bool DiscSwap(u32 fileflags=0);
+extern signed int sns_asc;
+extern signed int sns_ascq;
+extern signed int sns_key;
+
 
 void PatchRegion_0(u8* sector,int size);
 void PatchRegion_6(u8* sector,int size);
@@ -292,4 +297,6 @@ struct RawTrackFile : TrackFile
 	}
 };
 
-DiscType GuessDiscType(bool m1, bool m2, bool da);
+DiscType GuessDiscType(bool m1, bool m2, bool da);
+
+extern void gd_setdisc()

core/windows/winmain.cpp

@@ -1,5 +1,6 @@
 #include "oslib\oslib.h"
 #include "oslib\audiostream_rif.h"
+#include "imgread\common.h"
 
 #define _WIN32_WINNT 0x0500 
 #include <windows.h>
@@ -229,6 +230,9 @@ void UpdateInputState(u32 port)
 
 		if (GetAsyncKeyState('2'))
 			settings.pvr.ta_skip = 0;
+
+		if (GetAsyncKeyState('0'))
+			DiscSwap();
 	}