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https://gitlab.com/freepascal.org/fpc/source.git
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102 lines
2.5 KiB
ObjectPascal
102 lines
2.5 KiB
ObjectPascal
{ This example shows the difference between protected and real mode
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interrupts; it redirects the protected mode handler to an own handler
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which returns an impossible function result and calls it afterwards.
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Then the real mode handler is called directly, to show the difference
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between the two.
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Used Interrupt:
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get DOS version Int 21h / function 30h
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Input: AH = $30
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AL = $1
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Return: AL = major version number
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AH = minor version number
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}
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uses
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crt,
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go32;
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var
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r : trealregs;
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{ temporary variable used for the protected mode int call }
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axreg : Word;
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oldint21h : tseginfo;
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newint21h : tseginfo;
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{ this is our int 21h protected mode interupt handler. It catches
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the function call to get the DOS version, all other int 21h calls
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are redirected to the old handler; it is written in assembly
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because the old handler can't be called with pascal }
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procedure int21h_handler; assembler;
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asm
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cmpw $0x3001, %ax
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jne .LCallOld
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movw $0x3112, %ax
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iret
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.LCallOld:
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ljmp %cs:oldint21h
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end;
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{ a small helper procedure, which waits for a keypress }
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procedure resume;
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begin
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Writeln;
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Write('-- press any key to resume --'); readkey;
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gotoxy(1, wherey); clreol;
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end;
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begin
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{ see the text messages for further detail }
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clrscr;
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Writeln('Executing real mode interrupt');
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resume;
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r.ah := $30; r.al := $01; realintr($21, r);
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Writeln('DOS v', r.al,'.',r.ah, ' detected');
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resume;
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Writeln('Executing protected mode interrupt without our own',
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' handler');
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Writeln;
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asm
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movb $0x30, %ah
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movb $0x01, %al
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int $0x21
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movw %ax, axreg
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end;
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Writeln('DOS v', r.al,'.',r.ah, ' detected');
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resume;
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Writeln('As you can see the DPMI hosts default protected mode',
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'handler');
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Writeln('simply redirects it to the real mode handler');
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resume;
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Writeln('Now exchanging the protected mode interrupt with our ',
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'own handler');
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resume;
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newint21h.offset := @int21h_handler;
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newint21h.segment := get_cs;
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get_pm_interrupt($21, oldint21h);
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set_pm_interrupt($21, newint21h);
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Writeln('Executing real mode interrupt again');
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resume;
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r.ah := $30; r.al := $01; realintr($21, r);
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Writeln('DOS v', r.al,'.',r.ah, ' detected');
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Writeln;
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Writeln('See, it didn''t change in any way.');
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resume;
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Writeln('Now calling protected mode interrupt');
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resume;
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asm
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movb $0x30, %ah
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movb $0x01, %al
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int $0x21
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movw %ax, axreg
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end;
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Writeln('DOS v', lo(axreg),'.',hi(axreg), ' detected');
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Writeln;
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Writeln('Now you can see that there''s a distinction between ',
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'the two ways of calling interrupts...');
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set_pm_interrupt($21, oldint21h);
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end. |