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Work around broken BIOSes which report random API subset support bitmaps

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when checking for extended INT13 availability for CDROMs

svn path=/trunk/; revision=11741
This commit is contained in:
Gé van Geldorp 2004-11-21 12:27:01 +00:00
parent df6bd1fced
commit 4d111bdd6c
1 changed files with 19 additions and 3 deletions
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22
freeldr/freeldr/arch/i386/pcdisk.c
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@ -266,11 +266,21 @@ static BOOL PcDiskReadLogicalSectorsCHS(U32 DriveNumber, U64 SectorNumber, U32 S
static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
{
static U32 LastDriveNumber = 0xffffffff;
static BOOL LastSupported;
REGS RegsIn;
REGS RegsOut;
DbgPrint((DPRINT_DISK, "PcDiskInt13ExtensionsSupported()\n"));
if (DriveNumber == LastDriveNumber)
{
DbgPrint((DPRINT_DISK, "Using cached value %s for drive 0x%x\n", LastSupported ? "TRUE" : "FALSE", DriveNumber));
return LastSupported;
}
LastDriveNumber = DriveNumber;
// IBM/MS INT 13 Extensions - INSTALLATION CHECK
// AH = 41h
// BX = 55AAh
@ -305,12 +315,14 @@ static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
if (!INT386_SUCCESS(RegsOut))
{
// CF set on error (extensions not supported)
LastSupported = FALSE;
return FALSE;
}
if (RegsOut.w.bx != 0xAA55)
{
// BX = AA55h if installed
LastSupported = FALSE;
return FALSE;
}
@ -323,17 +335,21 @@ static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
{
// CX = API subset support bitmap
// Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
LastSupported = FALSE;
return FALSE;
}
#endif
// Use this relaxed check instead
if (RegsOut.w.cx == 0x0000)
// Use this relaxed check instead (most BIOSes seem to use 0x9f as CD-Rom)
if (RegsOut.w.cx == 0x0000 && DriveNumber != 0x9f)
{
// CX = API subset support bitmap
return FALSE;
printf("Suspicious API subset support bitmap 0x%x on device 0x%x\n", RegsOut.w.cx, DriveNumber);
LastSupported = FALSE;
return LastSupported;
}
LastSupported = TRUE;
return TRUE;
}