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MMU description » History » Version 12

Taya Sergeeva, 02/11/2013 05:14 PM

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h1. MMU description
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Documentation with examples
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The MMU grammar is in ru.ispras.microtesk.translator.mmu.grammar folder. It contains Lexer, Parser and TreeWalker files. These files can be built by build.xml file (microtesk++/build.xml). The files generated (MMULexer.java, MMUParser.java, MMUTreeWalker.java) are in microtesk++.gen.ru.ispras.microtesk.translator.mmu.grammar folder. 
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The folder ru.ispras.microtesk.translator.mmu.ir. contains the inner representation of the MMU hierarchy of one buffer.  
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MMU translator is in the ru.ispras.microtesk.translator.mmu.translator folder. After grammar files being generated the file ''BufferExample'' can be loaded to this translator.
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For instance, this is an example of such file below:
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<pre>
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address PA  
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{
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	width = 40
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}
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buffer L1 
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{
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	sets = 4
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	lines = 128
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	line = (tag:30 data:256)
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	index(addr:PA) = addr<9**8> 
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	match(addr:PA) = line.tag == addr<39**10>	
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	policy =  lru
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}
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</pre>
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Files in ru.ispras.microtesk.model.api.mmu folder contains different policies of cache.  Folder ru.ispras.microtesk.model.api.mmu.buffer contains the model of MMU - the files which describe Buffer, Set, Line, Address expressions.  
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Buffer can be described by different parameters, such sets, lines, index, match, policy, and so on, which number is infixed.
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Description of each constructor in the buffer example is below:
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* ''set'' is an associativity of a buffer; it returns the number of lines in a one set;
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* ''lines'' is the number of lines in a given buffer;
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* ''line'' designates the specific line in which the necessary data will be looking for; 
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  ''line'' includes its own parameters in the braces: ''tag'' and ''data'', each of them has an appropriate width of the fields kept in bytes;
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  in our example ''line'' has only two parameters, but in general case it can include more;
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* ''index'' returns the initial and the final points of the field kept in bytes; they are marked in a three-cornered brackets, after ''addr'';
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  ''index'' depends on an ''address'', which is ''physical'' (PA) in our case; the type of an address is set in the braces after ''index''; 
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* ''match'' returns ''true'' or ''false'' depending on if the data required is in the given line or not; it returns ''true'' if there is a ''hit'' in the line, and returns ''false'' otherwise;
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  ''match'' description contains the the initial and the final points of the address field in the triangle brackets after ''addr''; 
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  as ''index'' in the round braces ''match'' also has the type of the address used; ''PA'' in our case;
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* ''policy'' sets a policy which will be applied to our buffer in a cache, ''lru'' (Least Recently Used) in our example.