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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html><head><meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> <title>Jumps</title> <link href="doxygen.css" rel="stylesheet" type="text/css"> </head><body> <!-- Generated by Doxygen 1.2.16 --> <center> <a class="qindex" href="main.html">Main Page</a> <a class="qindex" href="modules.html">Modules</a> <a class="qindex" href="pages.html">Related Pages</a> </center> <hr><h1>Jumps<br> <small> [<a class="el" href="group__pavr__pipeline.html">Pipeline details</a>]</small> </h1><table border=0 cellpadding=0 cellspacing=0> </table> <dl compact><dt><b> A few details</b><dd> There are 4 jump instructions: <ul> <li> RJMP (relative jump) <br> The jump address is obtained by adding to the current Program Counter a 12 bit signed offset obtained from the instruction word. <li> IJMP (indirect jump) <br> The jump address is read from the Z pointer register. <br> The jump destination resides in the lower 64 Kwords of Program Memory. <br> <li> EIJMP (extended indirect jump) <br> The jump address is read from EIND:Z (higher 6 bis from EIND register in IOF, and lower 16 bits from Z pointer in RF). <br> This jump accesses the whole 22 bit addressing space of the Program Memory. <br> <li> JMP (long jump) <br> The jump address is read from two consecutive instruction words. <br> This jump accesses the whole 22 bit addressing space of the Program Memory. <br> </ul> <br> When a jump is detected into the pipeline, next two instructions (that were already uselessly fetched from the Program Memory) are flushed. Then, the Program Memory manager is asked permission to access the Program Memory and to modify the instruction flow (modify the Program Counter). <br> After that, unless it gets flushed or stalled by an older instruction, the jump instruction will configure the pipeline to fetch from the new PM address. <br> <br> RJMP and JMP take 3 clocks, while IJMP and EIJMP take 4 clocks. <br> </dl><dl compact><dt><b> Jump state machine</b><dd> <br> <div align="center"> <img src="pavr_pipe_jumps_01.gif" alt="pavr_pipe_jumps_01.gif"> </div> <br> </dl><hr><address align="right"><small>Generated on Tue Dec 31 20:26:31 2002 for Pipelined AVR microcontroller by <a href="http://www.doxygen.org/index.html"> <img src="doxygen.png" alt="doxygen" align="middle" border=0 width=110 height=53></a>1.2.16 </small></address> </body> </html>