+++ /dev/null
-Overview
-========
-This is SLICC, a domain specific language to specify cache coherence protocol
-we have developed in Multifacet group.
-
-It is developed by Milo Martin <milo@cs.wisc.edu>
-This document is prepared by Min Xu <mxu@cae.wisc.edu> while I am learning the
-system. With minor correctness updates by Brad Beckmann <beckmann@cs.wisc.edu>
-
-It can be used to generate C++ code that works with RUBY cache simulator as
-well as generate HTML and other document to describe the target protocol.
-
-Some user document is available in doc directory.
-
-Tech details
-============
-SLICC take a text input with similar syntax to C++ language and use the lexer
-and parser in parser directory to construct a Abstract Syntax Tree (AST)
-internally. After having done this first pass, the AST is traversed to fill
-several interval table, such as symbol table, type table, etc. Finally the code
-is generated by traversing the tree once again.
-
-Note, by Milo's good coding habit, almost all C++ class define their private
-copy/assignment constructor. This prevents accidentally copying/assigning an
-object by its address.
-
-The AST basically looks like a hierarchical representation of the text input.
-At the highest level, it has the "Machine", each Machine has several "states"
-and "events" and "actions" and "transistions".
-
-Since the language is domain specific, many assumptions of the target system is
-hardcoded in SLICC. For example, ruby would expect the generated code for each
-system node, has the following components:
- processor(sequencer, not generated?)
- cache
- directory (with memory block value, only when compiled with tester)
- network interface (NI)
-
-Directory generator/ contains routines to generate HTML/MIF format output.
-fileio.[Ch] has a routine to conditionally write a file only when the original
-content of the file is different from what is going to be written, this avoid
-re-make those file after regenerate the protocol. html_gen.[Ch] contains the
-symbol name munge and index page generation. mif_gen.[Ch] contains the entire
-MIF output generation routine, mainly a table buildup.
-
-Directory symbol/ contains classes to represent symbols in the slicc input
-file. Base class is "Symbol". Derived subclasses are "Action Event Func State
-StateMachine Transition Type Var". "Symbol" has knowledge about its locations
-in the source file and short name, long name. "SymbolTable" is a list of
-symbols and g_sym_table is the global SymbolTable of the slicc system.
-One can query a SymbolTable by symbol's id. Also SymbolTable is responsible for
-keeping track of Symbol's declaration in correct scope. The current
-implementation uses a stack which dynamically determine the scope of symbol
-lookups. Global scope is at bottom of the stack (vector[0]). SymbolTable is
-also the main place to write out the generated C++/HTML/MIF files.
-SymbolTable::writeNodeFiles() is one of the place to look for hardcoded C++
-code for node.[Ch]. And Type.[Ch] is the place where generating enumeration and
-Message/NetworkMessage declaration and implementation. Func.[Ch] is used to
-generate function of the class Chip. StateMachine.[Ch] wrap the whole thing
-up by putting States, Actions, Events together. It actually has a two dimension
-table like the one represented in the HTML output. Actions are indexed with
-the initial state and observed event. After the tabel being built, the
-StateMachine class can write out Transitions/Controller/wakeup_logic into C++
-outputs. Finally, in symbol directory, Var.[Ch] seem to incomplete?
-
-Demystify all those "predefined" external types, like "Address". Where are
-they defined? They are in ../protocol/RubySlicc-*.sm and
-../protocol/RubySlicc_interfaces.slicc is include in the slicc invocation
-command in ../ruby/Makefile.
-
-Another myth: "trigger" method is hardcoded in ast/InPortDeclAST.C and
-ast/FuncCallExprAST.C. The function is similar to inlined function in the
-output generated code, so you cannot find any occurance of string "trigger" in
-the generated code. "trigger" also increment a counter that is checked every
-time a transition is done. In one ruby cycle, only TRANSITIONS_PER_RUBY_CYCLE
-number of transitions can be done. ast/FuncCallExprAST.C also contains some
-code for function "error" and "assert" and "DEBUG_EXPR", all in the same
-manner. Ruby always issues transitions from the first port while there is any.
-Stalled transition in Ruby does not consume a sub-cycle. This models the
-hardware that probe all port in parallel, pick one transition from the highest
-priority queue if the transistion was not stalled by any resources constraint.
-
-Another note: scheduleEvent() call of ruby make sure a consumer is woken up at
-specified cycle, and only once per cycle.
-
-Action z_stall, where is it? It is hardcoded in symbols/StateMachine.C. In
-function StateMachine::printCSwitch(), z_stall cause the generated code return
-TransitionResult_ProtocolStall. Also the HTML output for z_stall has to be
-consequently hardcoded. I am not sure that's really a good idea or not. :-)
-
-Question: How comes there is no "for" loop statement in slicc?
-Answer: Been there, done that. That is easy to add, first of all. But unbound
-loop make slicc eventually un-synthesizable. We want to avoid that. If you want
-to loop through a bounded array do something, make the action done in a
-external interface in RubySlicc_Util.h. Inside, you just pass the vector as
-parameter to the external interface to achieve the same effects.
-
-Another bad thing of using loop statement like for is that we can not determine
-how many buffer space to allocate before the transition. With a vector, if it
-easy to understand we can always allocate the worst case number of hardware
-resources.
-
-Question: Wait! It seems statement check_allocate does nothing!
-Answer: No, it does call areNSoltsAvailable() function of the object before any
-statement is executed in one action. It does *NOT* generate code in its
-original place in the code, instead, it scan the body of the action code and
-determine how many slots are needed to allocated before hand. So the
-transaction is all done or nothing done. I had tried to make all actions return
-boolean values and the false return cause a transition to abort with
-ResourceStall. But it is later on deemed to be too flexible in its semantics.
-We should never introduce control flow inside the transitions, so that each
-transition is either "all" or "nothing". Just that simple. BTW, if you call
-check_allocate twice, areNSoltsAvailable(2) is generated, three times generates
-areNSoltsAvailable(3), etc.
projects / gem5.git / commitdiff