mirror of
https://gitlab.com/freepascal.org/fpc/source.git
synced 2025-04-12 22:49:34 +02:00
80 lines
1.7 KiB
ObjectPascal
80 lines
1.7 KiB
ObjectPascal
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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axreg : Word;
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oldint21h : tseginfo;
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newint21h : tseginfo;
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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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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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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. |