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<concept id="GUID-C059F39F-BC53-5C92-B05E-863B8CF22859" xml:lang="en"><title>Command

Objects</title><shortdesc>The MultiMediaCard controller uses a <codeph>TMMCCommandDesc</codeph> object

to contain command and parameter information when issuing a command over the

bus.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> This object is also used to contain response information resulting from

the execution of that command. </p>

<p>As it can sometimes be necessary to temporarily save current command and

parameter information, the controller implements a small stack of <xref href="GUID-6B3DDBFD-3A4A-3694-A058-7794700FEC7A.dita"><apiname>TMMCCommandDesc</apiname></xref> objects.

The controller then has the concept of a <i>current</i> command information

object. </p>

<p>The platform independent layer provides three functions through which command

and parameter information can be set up: </p>

<ul>

<li id="GUID-2E6A2192-CC7E-519C-9918-F9A21A340D7B"><p>Two variants of <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-DBD4FF2D-5443-3993-B63E-A19606D07C92"><apiname>DMMCStack::CurrentSessFillCmdDesc()</apiname></xref> </p> </li>

<li id="GUID-95BD9ED0-773A-588E-801E-F248745A2160"><p> <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-0629AAB8-4F6D-363D-ACCD-EAD31B884211"><apiname>DMMCStack::CurrentSessFillCmdArgs()</apiname></xref> </p> </li>

</ul>

<p>These functions are used to fill the <i>current</i> <xref href="GUID-6B3DDBFD-3A4A-3694-A058-7794700FEC7A.dita"><apiname>TMMCCommandDesc</apiname></xref> object. </p>

<p>The controller executes a single command by calling the state machine function <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-A48C1C16-B465-3DDA-9C83-00DEB8D27B68"><apiname>DMMCStack::IssueMMCCommandSM()</apiname></xref>;

this is implemented by the platform specific layer as part of the porting

activity. </p>

<p>It calls <xref href="GUID-0186BEDE-8E28-3F8C-8CAE-A8B92F41F47A.dita#GUID-0186BEDE-8E28-3F8C-8CAE-A8B92F41F47A/GUID-931547BD-665D-326A-92B5-909B2D57F8C6"><apiname>DMMCSession::Command()</apiname></xref> to access the <i>current</i> command

and parameter information. </p>

<section id="GUID-0F16D5E0-9A9F-597C-9865-4D44C39BD78E"><title>The command

stack</title> <p>Internally, the command stack is implemented as a simple

array of <xref href="GUID-6B3DDBFD-3A4A-3694-A058-7794700FEC7A.dita"><apiname>TMMCCommandDesc</apiname></xref> objects; this is the <codeph>DMMCSession::iCommand[]</codeph> private

data member. The stack is <codeph>KMaxMMCCommandStackDepth</codeph> deep.

Internally, the current command information object is identified and accessed

through the <codeph>DMMCSession::iCmdSP</codeph> data member, which indexes

into the array and acts as a pointer to the current command information object. </p> <p>The

platform independent layer provides two protected functions that the platform

specific layer can use to change the command information object that is current: </p> <ul>

<li id="GUID-6DAD8BE5-666C-5C4D-AC45-D5D8BA4E952F"><p> <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-FE93890C-249A-3344-BC93-57E690A432C4"><apiname>DMMCStack::CurrentSessPushCmdStack()</apiname></xref> </p> </li>

<li id="GUID-302438B8-7501-50DE-96FE-8AE7BA3D88B1"><p> <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-7B55B7E8-373D-39BE-BB15-A9F41E6A0255"><apiname>DMMCStack::CurrentSessPopCmdStack()</apiname></xref> </p> </li>

</ul> </section>

</conbody></concept>