Lavniveau program modellering eksempel

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=50 BGCOLOR="#333366" TEXT="#080000"> <div> <B>Lavniveau program modellering eksempel</B></div> <div> </div> </td> </tr><tr> <td valign="top" width=165 BGCOLOR="#CCCC99" TEXT="#080000"> <div> <B> <TABLE BORDER="0" CELLPADDING="2" CELLSPACING="1" WIDTH="132" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" ALIGN="BOTTOM" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP HEIGHT= 35 ><NOBR><div> <IMG BORDER="0" SRC="1x1.gif" HEIGHT="29" ALIGN="BOTTOM" HSPACE="0" VSPACE="0" WIDTH="21"></div> </NOBR></tD> <tD VALIGN=TOP><NOBR><div> <IMG BORDER="0" SRC="1x1.gif" HEIGHT="29" ALIGN="BOTTOM" HSPACE="0" VSPACE="0" WIDTH="21"></div> </NOBR></tD> <tD VALIGN=TOP WIDTH="20"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="35" ALIGN="bottom" WIDTH="20" HSPACE="0" VSPACE="0"></tD> <tD VALIGN=TOP><NOBR><div> <A HREF="id378.htm" TARGET="_top" TITLE="Lavniveau program modellering"><U><B><IMG SRC="0c80d1d0.gif" border=0 width="13" height="29" ALT="up" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></U></A></div> </NOBR></tD> <tD VALIGN=TOP><NOBR><div> <A HREF="id794.htm" TARGET="_top" TITLE="push reg cli"><U><B><IMG SRC="0c71b1d0.gif" border=0 width="27" height="29" ALT="down" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></U></A></div> </NOBR></tD> </tR> </TABLE></B></div> <div> <A HREF="id794.htm" TARGET="_top" TITLE="push reg cli"><U><B>push reg cli</B></U></A></div> <div> <A HREF="id796.htm" TARGET="_top" TITLE="clicks offset count"><U><B>clicks offset count</B></U></A></div> <div> <A HREF="id797.htm" TARGET="_top" TITLE="block copy more next"><U><B>block copy more next</B></U></A></div> <div> <A HREF="id798.htm" TARGET="_top" TITLE="pop reg"><U><B>pop reg</B></U></A></div> <bR> <div> <A HREF="tanenbaum__1987__operating_systems.htm" TARGET="_top" TITLE="Operating Systems"><U><B>Tanenbaum [1987] Operating Systems</B></U></A></div> <bR> </td> <td valign="top" height=430 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> Generel systemmodellering af en funktion til kopiering af en blok data fra en adresse til en anden i computerens lager.</div> <bR> <div> Maskinkode program:</div> <bR> <div> <TABLE BORDER="2" CELLPADDING="2" CELLSPACING="1" WIDTH="477" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="VOID" RULES="COLS" ALIGN="BOTTOM" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP COLSPAN=2 HEIGHT= 30 WIDTH="467"><div> | This routine copies a block of physical memory. It is called by:</div> <div> |     phys_copy( (long) source, (long) destination, (long) bytecount)</div> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 222 WIDTH="180"><div> _phys_copy:</div> <div>      pushf</div> <div>      cli</div> <div>      push bp</div> <div>      push ax</div> <div>      push bx</div> <div>      push cx</div> <div>      push dx</div> <div>      push si</div> <div>      push di</div> <div>      push ds</div> <div>      push es</div> <div>      mov bp,sp</div> <bR> </tD> <tD VALIGN=TOP WIDTH="284"><bR> <div> save flags</div> <div> disable interrupts</div> <div> save the registers</div> <div> save ax</div> <div> save bx</div> <div> save cx</div> <div> save dx</div> <div> save si</div> <div> save di</div> <div> save ds</div> <div> save es</div> <div> set bp to point to saved es</div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 126 WIDTH="180"><div> L0:     mov ax,28(bp)</div> <div>      mov di,26(bp)</div> <div>      mov cx,*4</div> <div> L1:     rcr ax,*1</div> <div>      rcr di,*1</div> <div>      loop L1</div> <div>      mov es,di</div> <bR> </tD> <tD VALIGN=TOP><NOBR><div> ax = high-order word of 32-bit destination</div> <div> di = low-order word of 32-bit destination</div> <div> start extracting click number from dest</div> <div> click number is destination address / 16</div> <div> it is used in segment register for copy</div> <div> 4 bits of high-order word are used</div> <div> es = destination click</div> <bR> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 126 WIDTH="180"><div>      mov ax,24(bp)</div> <div>      mov si,22(bp)</div> <div>      mov cx,*4</div> <div> L2:     rcr ax,*1</div> <div>      rcr si,*1</div> <div>      loop L2</div> <div>      mov ds,si</div> <bR> </tD> <tD VALIGN=TOP><NOBR><div> ax = high-order word of 32-bit source</div> <div> si = low-order word of 32-bit source</div> <div> start extracting click number from source</div> <div> click number is source address / 16</div> <div> it is used in segment register for copy</div> <div> 4 bits of high-order word are used</div> <div> ds = source click</div> <bR> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 78 WIDTH="180"><div>      mov di,26(bp)</div> <div>      and di,*0x000F</div> <div>      mov si,22(bp)</div> <div>      and si,*0x000F</div> <bR> </tD> <tD VALIGN=TOP WIDTH="284"><div> di = low-order word of dest address</div> <div> di = offset from paragraph # in es</div> <div> si = low-order word of source address</div> <div> si = offset from paragraph # in ds</div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 46 WIDTH="180"><div>      mov dx,32(bp)</div> <div>      mov cx,30(bp)</div> <bR> </tD> <tD VALIGN=TOP WIDTH="284"><div> dx = high-order word of byte count</div> <div> cx = low-order word of byte count</div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 126 WIDTH="180"><div>      test cx,#0x8000</div> <div>      jnz L3</div> <div>      test dx,#0xFFFF</div> <div>      jnz L3</div> <div>      jmp L4</div> <div> L3:     mov cx,#0x8000</div> <div> L4:     mov ax,ax</div> <bR> </tD> <tD VALIGN=TOP><NOBR><div> if bytes >= 32768, only do 32768</div> <div> per iteration</div> <div> check high-order 17 bits to see if bytes</div> <div> if bytes >= 32768 then go to L3</div> <div> if bytes < 32768 then go to L4</div> <div> 0x8000 is unsigned 32768</div> <div> save actual count used in ax; needed later</div> <bR> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 94 WIDTH="180"><div>      test cx,*0x0001</div> <div>      jz L5</div> <div>      rep</div> <div>      movb</div> <div>      jmp L6</div> <bR> </tD> <tD VALIGN=TOP><NOBR><div> should we copy a byte or a word at a time?</div> <div> jump if even</div> <div> copy 1 byte at a time</div> <div> byte copy</div> <div> check for more bytes</div> <bR> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 62 WIDTH="180"><div> L5:     shr cx,*1</div> <div>      rep</div> <div>      movw</div> <bR> </tD> <tD VALIGN=TOP WIDTH="284"><div> word copy</div> <div> copy 1 word at a time</div> <div> word copy</div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 158 WIDTH="180"><div> L6:     mov dx,32(bp)</div> <div>      mov cx,30(bp)</div> <div>      xor bx,bx</div> <div>      sub cx,ax</div> <div>      sbb dx,bx</div> <div>      or cx,cx</div> <div>      jnz L7</div> <div>      or dx,dx</div> <div>      jnz L7</div> <bR> </tD> <tD VALIGN=TOP><NOBR><div> decr count, incr src & dst, iterate if needed</div> <div> dx || cx is 32-bit byte count</div> <div> bx || ax is 32-bit actual count used</div> <div> compute bytes - actual count</div> <div> dx || cx is # bytes not yet processed</div> <div> see if it is 0</div> <div> if more bytes then go to L7</div> <div> keep testing</div> <div> if loop done, fall through</div> <bR> </NOBR></tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 190 WIDTH="180"><div>      pop es</div> <div>      pop ds</div> <div>      pop di</div> <div>      pop si</div> <div>      pop dx</div> <div>      pop cx</div> <div>      pop bx</div> <div>      pop ax</div> <div>      pop bp</div> <div>      popf</div> <div>      ret</div> <bR> </tD> <tD VALIGN=TOP WIDTH="284"><div> restore all the saved registers</div> <div> restore ds</div> <div> restore di</div> <div> restore si</div> <div> restore dx</div> <div> restore cx</div> <div> restore bx</div> <div> restore ax</div> <div> restore bp</div> <div> restore flags</div> <div> return to caller</div> <bR> </tD> </tR> <tR> <tD VALIGN=TOP HEIGHT= 110 WIDTH="180"><div> L7:     mov 32(bp),dx</div> <div>      mov 30(bp),cx</div> <div>      add 26(bp),ax</div> <div>      adc 28(bp),bx</div> <div>      add 22(bp),ax</div> <div>      adc 24(bp),bx</div> <div>      jmp L0</div> </tD> <tD VALIGN=TOP><NOBR><div> store decremented byte count back in mem</div> <div> as a long</div> <div> increment destination</div> <div> carry from low-order word</div> <div> increment source</div> <div> carry from low-order word</div> <div> start next iteration</div> </NOBR></tD> </tR> </TABLE></div> <div> Kilde: <A HREF="tanenbaum__1987__operating_systems.htm" TARGET="_top" TITLE="Operating Systems"><U>Tanenbaum [1987] Operating Systems</U></A></div> <bR> <div> Overordnet generel systemmodel</div> <bR> <div> <IMG SRC="2ff8d410.gif" border=0 width="397" height="321" ALT="VISIO 5 Drawing" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> </td> </tr></table></body>