<html><head><title>Sequencer Classes</title><link rel="stylesheet" type="text/css" href="../styles/main.css"><script language=JavaScript src="../javascript/main.js"></script></head><body class="FramedContentPage" onLoad="NDOnLoad()"><script language=JavaScript><!--
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<div class="CSection"><div class=CTopic id=MainTopic><h1 class=CTitle><a name="Sequencer_Classes" href="../../ovm_ref/sequencers.txt">Sequencer Classes</a></h1><div class=CBody><p>The sequencer serves as an arbiter for controlling transaction flow from multiple stimulus generators.&nbsp; More specifically, the sequencer controls the flow of <a href="../files/methodology/sequences/ovm_sequence_item-svh.html#ovm_sequence_item" class=LClass id=link1 onMouseOver="ShowTip(event, 'tt1', 'link1')" onMouseOut="HideTip('tt1')">ovm_sequence_item</a>-based transactions generated by one or more <a href="../files/methodology/sequences/ovm_sequence-svh.html#ovm_sequence#(REQ,RSP)" class=LClass id=link2 onMouseOver="ShowTip(event, 'tt2', 'link2')" onMouseOut="HideTip('tt2')">ovm_sequence #(REQ,RSP)</a>-based sequences.</p><img src="nd/Images/ovm_ref_sequencer.gif" width="250" height="276"><p>There are two sequencer variants available.</p><ul><li><a href="../files/methodology/sequences/ovm_sequencer-svh.html#ovm_sequencer#(REQ,RSP)" class=LClass id=link3 onMouseOver="ShowTip(event, 'tt3', 'link3')" onMouseOut="HideTip('tt3')">ovm_sequencer #(REQ,RSP)</a> - Requests for new sequence items are initiated by the driver.&nbsp; Upon such requests, the sequencer selects a sequence from a list of available sequences to produce and deliver the next item to execute.&nbsp; This sequencer is typically connected to a user-extension of <a href="../files/methodology/ovm_driver-svh.html#ovm_driver#(REQ,RSP)" class=LClass id=link4 onMouseOver="ShowTip(event, 'tt4', 'link4')" onMouseOut="HideTip('tt4')">ovm_driver #(REQ,RSP)</a>.</li><li><a href="../files/methodology/sequences/ovm_push_sequencer-svh.html#ovm_push_sequencer#(REQ,RSP)" class=LClass id=link5 onMouseOver="ShowTip(event, 'tt5', 'link5')" onMouseOut="HideTip('tt5')">ovm_push_sequencer #(REQ,RSP)</a> - Sequence items (from the currently running sequences) are pushed by the sequencer to the driver, which blocks item flow when it is not ready to accept new transactions.&nbsp; This sequencer is typically connected to a user-extension of <a href="../files/methodology/ovm_push_driver-svh.html#ovm_push_driver#(REQ,RSP)" class=LClass id=link6 onMouseOver="ShowTip(event, 'tt6', 'link6')" onMouseOut="HideTip('tt6')">ovm_push_driver #(REQ,RSP)</a>.</li></ul><p>Sequencer-driver communication follows a <i>pull</i> or <i>push</i> semantic, depending on which sequencer type is used.&nbsp; However, sequence-sequencer communication is <i>always</i> initiated by the user-defined sequence, i.e. follows a push semantic.</p><p>See <a href="sequences-txt.html#Sequence_Classes" class=LSection id=link7 onMouseOver="ShowTip(event, 'tt7', 'link7')" onMouseOut="HideTip('tt7')">Sequence Classes</a> for an overview on sequences and sequence items.</p><h4 class=CHeading>Sequence Item Ports</h4><p>As with all OVM components, the sequencers and drivers described above use <a href="tlm_ifs_and_ports-txt.html#TLM_Interfaces,Ports,and_Exports" class=LSection id=link8 onMouseOver="ShowTip(event, 'tt8', 'link8')" onMouseOut="HideTip('tt8')">TLM Interfaces, Ports, and Exports</a> to communicate transactions.</p><p>The <a href="../files/methodology/sequences/ovm_sequencer-svh.html#ovm_sequencer#(REQ,RSP)" class=LClass id=link9 onMouseOver="ShowTip(event, 'tt3', 'link9')" onMouseOut="HideTip('tt3')">ovm_sequencer #(REQ,RSP)</a> and <a href="../files/methodology/ovm_driver-svh.html#ovm_driver#(REQ,RSP)" class=LClass id=link10 onMouseOver="ShowTip(event, 'tt4', 'link10')" onMouseOut="HideTip('tt4')">ovm_driver #(REQ,RSP)</a> pair also uses a <i>sequence item pull port</i> to achieve the special execution semantic needed by the sequencer-driver pair.</p><img src="nd/Images/ovm_ref_seq_item_ports.gif" width="493" height="233"><p>sequencers and drivers use a <i>seq_item_port</i> specifically supports sequencer-driver communication.&nbsp; Connections to these ports are made in the same fashion as the TLM ports.</p></div></div></div>

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<div class=CToolTip id="tt1"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td>class ovm_sequence_item extends ovm_transaction</td></tr></table></blockquote>The base class for user-defined sequence items and also the base class for the ovm_sequence class. </div></div><div class=CToolTip id="tt2"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td><table border=0 cellspacing=0 cellpadding=0><tr><td class=PBeforeParameters colspan=5>virtual class ovm_sequence #(</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>REQ</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> ovm_sequence_item,</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>RSP</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> REQ</td></tr><tr><td class=PAfterParameters colspan=5>) extends ovm_sequence_base</td></tr></table></td></tr></table></blockquote>The ovm_sequence class provides the interfaces necessary in order to create streams of sequence items and/or other sequences.</div></div><div class=CToolTip id="tt3"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td><table border=0 cellspacing=0 cellpadding=0><tr><td class=PBeforeParameters colspan=5>class ovm_sequencer #(</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>REQ</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> ovm_sequence_item,</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>RSP</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> REQ</td></tr><tr><td class=PAfterParameters colspan=5>) extends ovm_sequencer_param_base #(REQ, RSP)</td></tr></table></td></tr></table></blockquote></div></div><div class=CToolTip id="tt4"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td><table border=0 cellspacing=0 cellpadding=0><tr><td class=PBeforeParameters nowrap>class ovm_driver #(</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>REQ</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%>ovm_sequence_item,</td></tr><tr><td></td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>RSP</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%>REQ</td><td class=PAfterParameters nowrap>) extends ovm_component</td></tr></table></td></tr></table></blockquote>The base class for drivers that initiate requests for new transactions via a ovm_seq_item_pull_port. </div></div><div class=CToolTip id="tt5"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td><table border=0 cellspacing=0 cellpadding=0><tr><td class=PBeforeParameters colspan=5>class ovm_push_sequencer #(</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>REQ</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> ovm_sequence_item,</td></tr><tr><td>&nbsp;&nbsp;&nbsp;</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>RSP</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%> REQ</td></tr><tr><td class=PAfterParameters colspan=5>) extends ovm_sequencer_param_base #(REQ, RSP)</td></tr></table></td></tr></table></blockquote></div></div><div class=CToolTip id="tt6"><div class=CClass><blockquote><table border=0 cellspacing=0 cellpadding=0 class=Prototype><tr><td><table border=0 cellspacing=0 cellpadding=0><tr><td class=PBeforeParameters nowrap>class ovm_push_driver #(</td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>REQ</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%>ovm_sequence_item,</td></tr><tr><td></td><td class=PType nowrap>type&nbsp;</td><td class=PParameter nowrap>RSP</td><td class=PDefaultValuePrefix>&nbsp;=&nbsp;</td><td class=PDefaultValue width=100%>REQ</td><td class=PAfterParameters nowrap>) extends ovm_component</td></tr></table></td></tr></table></blockquote>Base class for a driver that passively receives transactions, i.e. </div></div><div class=CToolTip id="tt7"><div class=CSection>Sequences encapsulate user-defined procedures that generate multiple ovm_sequence_item-based transactions. </div></div><div class=CToolTip id="tt8"><div class=CSection>The OVM TLM library defines several abstract, transaction-level interfaces and the ports and exports that facilitate their use. </div></div><!--END_ND_TOOLTIPS-->

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