Add INT 13h AH=42 support for El Torito No Emulation boot

joncampbell123 · Mar 23, 2024 · bcfb979 · bcfb979
1 parent f1b5fc3
commit bcfb979
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Showing 4 changed files with 60 additions and 10 deletions.
diff --git a/include/bios_disk.h b/include/bios_disk.h
@@ -564,4 +564,7 @@ std::string PartitionIdentifyType(imageDisk *loadedDisk);
 void LogPrintPartitionTable(const std::vector<_PC98RawPartition> &parts);
 void LogPrintPartitionTable(const std::vector<partTable::partentry_t> &parts);
 
+extern unsigned char INT13_ElTorito_NoEmuDriveNumber;
+extern char INT13_ElTorito_NoEmuCDROMDrive;
+
 #endif
diff --git a/src/dos/dos_programs.cpp b/src/dos/dos_programs.cpp
@@ -2321,6 +2321,10 @@ class BOOT : public Program {
                 for(i=0;i<2048;i++) real_writeb((uint16_t)load_seg, (uint16_t)i+(s*2048), entries[i]);
             }
 
+            /* signal INT 13h to emulate a CD-ROM drive El Torito "no emulation" style */
+            INT13_ElTorito_NoEmuDriveNumber = 0x90;
+            INT13_ElTorito_NoEmuCDROMDrive = el_torito_cd_drive;
+
             SegSet16(cs, load_seg);
             SegSet16(ds, 0);
             SegSet16(es, 0);
@@ -2333,7 +2337,8 @@ class BOOT : public Program {
             reg_ecx = 0;
             reg_ebp = 0;
             reg_eax = 0;
-            reg_edx = 0;
+            /* ISOLINUX clearly assumes DL at entry contains the drive number and at no point from entry to INT 13h does it change the contents of DX */
+            reg_edx = INT13_ElTorito_NoEmuDriveNumber;
 #ifdef __WIN32__
             // let menu know it boots
             menu.boot=true;

diff --git a/src/ints/bios.cpp b/src/ints/bios.cpp
@@ -9172,6 +9172,9 @@ class BIOS:public Module_base{
 # endif
 #endif
 
+	INT13_ElTorito_NoEmuDriveNumber = 0;
+	INT13_ElTorito_NoEmuCDROMDrive = 0;
+
 	ACPI_mem_enable(false);
 	ACPI_REGION_SIZE = 0;
 	ACPI_BASE = 0;

diff --git a/src/ints/bios_disk.cpp b/src/ints/bios_disk.cpp
@@ -1815,10 +1815,17 @@ bool IDE_GetPhysGeometry(unsigned char disk,uint32_t &heads,uint32_t &cyl,uint32
 void IDE_EmuINT13DiskReadByBIOS_LBA(unsigned char disk,uint64_t lba);
 
 void diskio_delay(Bits value/*bytes*/, int type = -1);
+
+/* For El Torito "No emulation" INT 13 services */
+unsigned char INT13_ElTorito_NoEmuDriveNumber = 0;
+char INT13_ElTorito_NoEmuCDROMDrive = 0;
+
+bool GetMSCDEXDrive(unsigned char drive_letter, CDROM_Interface **_cdrom);
+
 
 static Bitu INT13_DiskHandler(void) {
     uint16_t segat, bufptr;
-    uint8_t sectbuf[512];
+    uint8_t sectbuf[2048/*CD-ROM support*/];
     uint8_t  drivenum;
     Bitu  i,t;
     last_drive = reg_dl;
@@ -2208,14 +2215,45 @@ static Bitu INT13_DiskHandler(void) {
         break;
     case 0x42: /* Extended Read Sectors From Drive */
         /* Read Disk Address Packet */
-        readDAP(SegValue(ds),reg_si);
-
-        if (dap.num==0) {
-            reg_ah = 0x01;
-            CALLBACK_SCF(true);
-            return CBRET_NONE;
-        }
-
+        readDAP(SegValue(ds),reg_si);
+
+        if (dap.num==0) {
+            reg_ah = 0x01;
+            CALLBACK_SCF(true);
+            return CBRET_NONE;
+        }
+        if (INT13_ElTorito_NoEmuDriveNumber != 0 && INT13_ElTorito_NoEmuDriveNumber == reg_dl) {
+                CDROM_Interface *src_drive = NULL;
+                if (!GetMSCDEXDrive(INT13_ElTorito_NoEmuCDROMDrive - 'A', &src_drive)) {
+                        reg_ah = 0x01;
+                        CALLBACK_SCF(true);
+                        return CBRET_NONE;
+                }
+
+                segat = dap.seg;
+                bufptr = dap.off;
+                for(i=0;i<dap.num;i++) {
+			static_assert( sizeof(sectbuf) >= 2048, "not big enough" );
+			diskio_delay(512);
+			if (killRead || !src_drive->ReadSectorsHost(sectbuf, false, dap.sector+i, 1)) {
+				// TODO: According to RBIL this should update the number of blocks field to what was successfully transferred
+				LOG_MSG("Error in CDROM read");
+				killRead = false;
+				reg_ah = 0x04;
+				CALLBACK_SCF(true);
+				return CBRET_NONE;
+			}
+
+			for(t=0;t<2048;t++) {
+                                real_writeb(segat,bufptr,sectbuf[t]);
+                                bufptr++;
+                        }
+                }
+                reg_ah = 0x00;
+                CALLBACK_SCF(false);
+                return CBRET_NONE;
+        }
+
         if (!any_images) {
             // Inherit the Earth cdrom (uses it as disk test)
             if (((reg_dl&0x80)==0x80) && (reg_dh==0) && ((reg_cl&0x3f)==1)) {
@@ -2243,6 +2281,7 @@ static Bitu INT13_DiskHandler(void) {
             IDE_EmuINT13DiskReadByBIOS_LBA(reg_dl,dap.sector+i);
 
             if((last_status != 0x00) || killRead) {
+                // TODO: According to RBIL this should update the number of blocks field to what was successfully transferred
                 LOG_MSG("Error in disk read");
                 killRead = false;
                 reg_ah = 0x04;