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+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.