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120 lines
3.3 KiB
ObjectPascal
120 lines
3.3 KiB
ObjectPascal
{ example for :
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interrupt redirection
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software vs. hardware interrupts
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set_pm_interrupt()
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get_pm_interrupt()
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get_cs()
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tseginfo
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trealregs
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processor access
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get_cs(), get_ds(), get_ss()
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}
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{ 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 which
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returns an impossible function result and calls it afterwards. Then the real
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mode handler is called directly, to show the difference 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 = $1
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Return: AL = major version number
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AH = minor version number
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}
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uses crt, { used for clreol(), gotoxy() }
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go32;
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{$ASMMODE DIRECT}
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var r : trealregs;
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axreg : Word; { temporary variable used for the protected mode int call }
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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 the function
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call to get the DOS version, all other int 21h calls are redirected to the
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old handler; it is written in assembly because the old handler can't be
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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 CallOld
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movw $0x3112, %ax
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iret
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CallOld:
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ljmp %cs:OLDHANDLER
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OLDHANDLER: .long 0
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.word 0
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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 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 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 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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{ storing old handler address in interrupt handler }
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asm
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movl _OLDINT21H, %eax
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movl %eax, OLDHANDLER
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movw 4+_OLDINT21H, %ax
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movw %ax, 4+OLDHANDLER
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end;
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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 the two ways of ');
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Writeln('calling interrupts...');
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set_pm_interrupt($21, oldint21h);
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end. |