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   <dl>
   <dt>authors</dt>
   <dd>Jason Lowe-Power</dd>
 </dl>

 <h1 id="introduction-to-ruby">Introduction to Ruby</h1>

 <p>Ruby comes from the <a href="http://research.cs.wisc.edu/gems/">multifacet GEMS
 project</a>. Ruby provides a detailed
 cache memory and cache coherence models as well as a detailed network
 model (Garnet).</p>

 <p>Ruby is flexible. It can model many different kinds of coherence
 implementations, including broadcast, directory, token, region-based
 coherence, and is simple to extend to new coherence models.</p>

 <p>Ruby is a mostly drop-in replacement for the classic memory system.
 There are interfaces between the classic gem5 MemObjects and Ruby, but
 for the most part, the classic caches and Ruby are not compatible.</p>

 <p>In this part of the book, we will first go through creating an example
 protocol from the protocol description to debugging and running the
 protocol.</p>

 <p>Before diving into a protocol, we will first talk about some of the
 architecture of Ruby. The most important structure in Ruby is the
 controller, or state machine. Controllers are implemented by writing a
 SLICC state machine file.</p>

 <p>SLICC is a domain-specific language (Specification Language including
 Cache Coherence) for specifying coherence protocols. SLICC files end in
 “.sm” because they are <em>state machine</em> files. Each file describes
 states, transitions from a begin to an end state on some event, and
 actions to take during the transition.</p>

 <p>Each coherence protocol is made up of multiple SLICC state machine
 files. These files are compiled with the SLICC compiler which is written
 in Python and part of the gem5 source. The SLICC compiler takes the
 state machine files and output a set of C++ files that are compiled with
 all of gem5’s other files. These files include the SimObject declaration
 file as well as implementation files for SimObjects and other C++
 objects.</p>

 <p>Currently, gem5 supports compiling only a single coherence protocol at a
 time. For instance, you can compile MI_example into gem5 (the default,
 poor performance, protocol), or you can use MESI_Two_Level. But, to
 use MESI_Two_Level, you have to recompile gem5 so the SLICC compiler
 can generate the correct files for the protocol. We discuss this further
 in the compilation section &lt;MSI-building-section&gt;</p>

 <p>Now, let’s dive into implementing our first coherence protocol!</p>

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	<div class="edit"><a href="https://github.com/gem5/new-website/tree/master/_pages/documentation/part3/MSIintro.md">Edit this page</a></div>
	<dl>
	<dt>authors</dt>
	<dd>Jason Lowe-Power</dd>
	</dl>

	<h1 id="introduction-to-ruby">Introduction to Ruby</h1>

	<p>Ruby comes from the <a href="http://research.cs.wisc.edu/gems/">multifacet GEMS
	project</a>. Ruby provides a detailed
	cache memory and cache coherence models as well as a detailed network
	model (Garnet).</p>

	<p>Ruby is flexible. It can model many different kinds of coherence
	implementations, including broadcast, directory, token, region-based
	coherence, and is simple to extend to new coherence models.</p>

	<p>Ruby is a mostly drop-in replacement for the classic memory system.
	There are interfaces between the classic gem5 MemObjects and Ruby, but
	for the most part, the classic caches and Ruby are not compatible.</p>

	<p>In this part of the book, we will first go through creating an example
	protocol from the protocol description to debugging and running the
	protocol.</p>

	<p>Before diving into a protocol, we will first talk about some of the
	architecture of Ruby. The most important structure in Ruby is the
	controller, or state machine. Controllers are implemented by writing a
	SLICC state machine file.</p>

	<p>SLICC is a domain-specific language (Specification Language including
	Cache Coherence) for specifying coherence protocols. SLICC files end in
	“.sm” because they are <em>state machine</em> files. Each file describes
	states, transitions from a begin to an end state on some event, and
	actions to take during the transition.</p>

	<p>Each coherence protocol is made up of multiple SLICC state machine
	files. These files are compiled with the SLICC compiler which is written
	in Python and part of the gem5 source. The SLICC compiler takes the
	state machine files and output a set of C++ files that are compiled with
	all of gem5’s other files. These files include the SimObject declaration
	file as well as implementation files for SimObjects and other C++
	objects.</p>

	<p>Currently, gem5 supports compiling only a single coherence protocol at a
	time. For instance, you can compile MI_example into gem5 (the default,
	poor performance, protocol), or you can use MESI_Two_Level. But, to
	use MESI_Two_Level, you have to recompile gem5 so the SLICC compiler
	can generate the correct files for the protocol. We discuss this further
	in the compilation section <MSI-building-section></p>

	<p>Now, let’s dive into implementing our first coherence protocol!</p>

	<br>

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