A Simulator and Debugger for the CHP Language —User Manual
Contents
1. The value you assign to it corresponds to the function s return value A function may contain nested functions and procedures but no processes Because there are no global variables and because function parameters are value parameters functions are free of side effects Also functions do not have a persistent state 1 4 3 Procedures procedure_definition procedure identifier value parameter result_parameter seq opt chp_body A procedure has no return type its call is a statement A procedure may contain nested functions and procedures but no processes A procedure can modify its environment by modifying result parameters but otherwise has no side effects nor a persistent state 1 4 4 Processes process_definition process identifier meta_parameterseg opt port_parameterseg opt process_body port_parameter identifier direction jis type identifier list direction D 4 Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 11 process_body chp_body meta_body Processes have no value or result parameters instead they have meta parameters and ports Port parameters of the first form are data ports used for sending and receiving values A indicates an input port a indicates an output port The type is the data type of the port Port parameters of the second form are synchronization ports Processes are not called but instantiated Within a pr2. it is an error if more than one guard is true at the time the choice is made If the separator is an arbitrary choice is made among the guarded commands with a true guard The last form of the loop_statement executes the statement sequence repeatedly forever 1 5 4 Selection selection_statement guardedccommand guarded_command series opt I guardedcommand guarded command series opt l bool expr Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 14 chpsim 1 2 The first two forms of the selection_statement wait until one of the guarded commands has a true guard then execute one of the guarded commands that has a true guard The distinction between the first two forms is the same as for the oop_statement with the separator it is an error if more than one guard is true The last form of selection statement simply waits until the expression which must have bool type is true 1 5 5 Procedure call procedure_call identifier eXpPiist opt Yop The identifier must be the name of a procedure not of a function The argument expressions match the parameters of the procedure in order Let expression x match parameter p If p is a val or valres parameter the assignment p x is performed at the start of the procedure call If p is ares or valres parameter the assignment x p is performed at the end of the procedure call In all cases the standard rules for the assignment
3. The result type is a generic record with as field types the generic types of the expressions A record_constructor is not an value 1 6 4 3 Function call function call identifier expriist The identifier must be the name of a function The requirements for the arguments are the same as for procedure calls Section 1 5 5 but only value parameters are allowed Note that a function must have at least one parameter The type of the expression is the return type of the function A function call is not an value If all arguments are constants the function call is also a constant 1 6 5 Literals literal integer_literal character_literal string_literal symbol literal boolean_literal ooo Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 19 symbol literal identifier boolean literal false true Literals are never values Integer literals have type int Character literals have type type char 0 127 Their values correspond to ASCII codes A string literal is a 0 terminated generic array of int similar to an array_constructor A symbol_literal must have been declared as part of a symbol type 1 7 Meta processes meta_body meta definition meta_declaration series opt parallel_statement seq opt A meta process is a process with a meta_body The form of a meta process is nearly the same as that of a CHP process but there are some statements and declarations t
4. a traceall Trace all process instances This will generate a lot of output for anything but the shortest programs In most cases judiciously placed breakpoints are more helpful Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 24 chpsim 1 2 2 2 Execution At any time the simulator executes a number of threads in parallel Typically there is one thread per process instance but if a process executes a parallel statement statements separated by commas it has temporarily multiple threads Each thread can be active ready or suspended The simulator s print command lists the current threads cmnd print active q 0 r at example chp 42 2 active tgt at example chp 53 17 suspended srce at example chp 63 17 The example shows that there are three threads corresponding to three process instances The names starting with a slash are hierarchical instance names constructed from the identifiers in instance declarations Section 1 7 1 The initial process has as name merely a slash Hence q 0 ris instance r created by q 0 which itself was instantiated by the initial process An indication like example chp 42 2 gives respectively the source file the line number and the position on the line of the statement that will be executed next by the thread The simulator executes one non composite CHP statement at a time chosen from among the active threads Execution is fair an
5. active statement will eventually be executed a suspended statement will eventually be checked to determine whether it can be made active again The simulation consists of two phases the instantiation phase and the execution phase The simulation starts by creating a single instance of the initial process Typically this is a meta process that instantiates other child processes As explained in Section 1 7 child processes only start executing when their parent process has terminated Furthermore CHP processes only start executing when all meta processes have terminated which is the end of the instantiation phase The initial process may be a CHP process in which case the execution phase starts immediately 2 2 1 The current statement When the simulator stops to allow input of a command it prints the statement that will be executed next and the instance it belongs too Except after a warning or error in which case the printed statement was already executed This is the current statement which is the focus of most simulator commands When no process instance is mentioned most commands apply to the current statement or the current instance Some commands allow you to select an instance explicitly For convenience several of the simulator commands such as t race allow you to reference process instances that have not yet been created The view up and down commands let you change the instance and statement that have the focus This is ma
6. apply In addition the same value may not be used for two different result parameters The parentheses are optional if the argument list is empty 1 6 Expressions const_expr expr expr binary_expr An expression is a constant expression if all its constituent expressions are constants 1 6 1 Binary expressions binary_expr prefix_expr binary expr binary_operator binary_expr binary_operator D Z D mod I I xor Il ie lt I gt I gt s Il I l a amp i I The ambiguity in the syntax of binary expressions is resolved by using operator precedence Each line in the definition of binary_operator corresponds to a precedence level the first line has the highest level i e binds the tightest Operators listed on the same line have equal precedence Among operators with equal precedence the order is left to right i e all operators are left associative Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 15 A binary expression is not an value 1 6 1 1 Arithmetic operators The following operators require that their operands have generic type int the result of the operation has type int mod denotes exponentiation 2 N means 2 Since the result is an integer the second operand must be gt 0 x 1 always is integer division rounding towards 0 Consider a b If a and b have the same sign the result is gt 0
7. followed by an instance name prints the values of the instance s meta parameters the other processes the instance is connected to and the current position in the code print followed by a variable or constant name prints the value of that variable or constant The name must be in scope at the current position in the code 2 2 6 Other commands The help command prints a command summary The batch command switches to non interactive execution without stopping for more user input just like the batch option described in Section 2 1 Interrupting the program with ctrl c forces the simulator to stop at the next statement regardless of the instance This is useful if the program gets stuck in an infinite or very long loop In batch mode ct r1 C simply terminates the simulation The simulator also stops immediately after a statement that caused a warning or error message so that you can inspect variables etc The computation cannot continue following an error instead the simulator will terminate The quit command also terminates the simulation 2 3 Built in procedures The simulator has a few built in procedures that can be called from your CHP program to help with testing and debugging These are always available unless you have redefined the identifiers Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 27 procedure step This routine executes the simulator s st ep command The effect is that
8. identifier The postfix_expr must have a specific record type or have generic type int The expression is an value if the postfix_expr is an value In case of a record type the identifier must be one of the record s field names The result type is the type of the field If the postfix_expr 1s an integer the identifier must be a field name defined with a field_definition Section 1 2 2 1 This specifies a slice of the integer and is completely equivalent to the array notation for slices explained in Section 1 6 3 2 Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 18 chpsim 1 2 1 6 4 Atoms atom identifier literal array constructor l record_constructor function_call l expr An identifier used as atom is an value if it is the name of a variable or parameter the name of a function is also an value inside that function As mentioned in Section 1 4 6 variables parameters and function names used as variables can only be accessed in their own scope not in nested routines Other identifiers used as atom should be the names of constants or symbol literals Parentheses do not affect whether an expression is an value 1 6 4 1 Array constructor array_constructor expriist The expression must all have the same generic type T The result type is a generic array of T An array _constructor is not an value 1 6 4 2 Record constructor record_constructor CXPF list
9. may be a meta process or a CHP process Normally identifiers are declared immediately when they are encountered but as a special case instance names are only declared after parsing the process_type this means the instance name may be identical to the process name assuming they are declared at different scope levels Although an instance declaration creates the process instance it does not specify the values of the instance s meta parameters nor its connections to other processes These must be specified with subsequent statements 1 7 2 Meta parameters meta_parameter identifier tist meta_type meta_type lype Meta parameters get their value during the instantiation phase Although their values are not known at compile time nevertheless they are considered constants In the future there may be meta types that are not CHP types Meta parameters are given a value with a meta_binding meta_binding instance_expr expr jist instance _expr postfix_expr The instance_expr must be one of the process instances declared with instance The argument expressions must match the meta parameters of the corresponding process just as with function parameters There must be a meta_binding for each process instance that has meta parameters 1 7 3 Connecting processes connection connect connection_point connection point connection_point port_expr instance_expr_ identifier The first form of connection_point identifies
10. must be an input port and the value received is assigned to the value The peek receives a value without removing it from the port hence a subsequent receive or peek will receive the same value The first port of a pass must be an output port the second must be an input port The pass receives a value from the input port and simultaneously without introducing slack sends it via the output port The value received must be valid for the data type of the output port All communication actions including the peek suspend until they can complete A suspended peek does not cause the probe of the connected port to be true A suspended pass passes the probe from one side to the other but does not by itself cause a true probe The other communications when suspended cause the probe of the connected port to be true 1 5 3 Repetition loop_statement guarded command guarded command hseries opt guardedcommand guarded command h series opt l parallel_statementseq guarded_command bool_expr gt parallel_statementrseq bool_expr expr The guard of a guarded command i e the expression before the arrow must have bool type Execution of a guarded command consists of execution of the statement sequence The first two forms of the loop_statement choose one guarded command that has a true guard and execute it This process is repeated until no guard is true If the guarded commands are separated by symbols
11. names defined in the source file itself Importing is not recursive It is allowed to have circular dependencies between modules E g ml may require m2 while m2 requires m1 It makes sense to allow this since routines can be defined in any order Section 1 4 6 However there is an important restriction on such circular dependencies If module m1 has a circular dependency with module m2 then the top level declarations of m1 must not depend on m2 Top level declarations are the definitions in the syntax of source file but for routines the restriction only applies to the parameters and return type not to the body The following example is correct code file ml requires m2 export type color red green blue export function f1 x color 0 255 CHP var y byte y 2 0 tls y 1 file m2 requires m1 export type byte 0 255 export function f2 x byte byte CHP f2 x 2 export function g2 x byte byte CHP g2 fl blue However the restriction prevents us from changing the return type of f1 to byte because the return type is part of m1 s top level declarations If we want to share the definition of byte we should put it in a third module that is imported by both m1 and m2 Although importing is not recursive the notion of dependency is transitive Hence there can be circular dependencies involving more than two files The restriction applies to any two modules in the sam
12. otherwise the result is lt 0 is the remainder of division The sign of a b is the sign of a mod on the other hand is the standard modulo operation which always yields a non negative result a mod b a mod b The operations are summarized by the following example 10 3 3 10 3 1 10mod 3 1 10 3 3 10 3 1 l0 mod 3 2 10 3 3 10 3 1 10 mod 3 1 10 3 3 10 3 1 1l0 mod 3 2 The and mod operators require that their second operand is not 0 1 6 1 2 Comparison The lt lt gt and gt operators all yield a bool result Their operands must either both have generic type int or both have type bool where false lt true The and operators also yield a bool result They require that both operands have the same generic type 1 6 1 3 Logical and bitwise operators The amp and xor operators require that either both operands have type bool or both operands have generic type int If the operands have type bool the result also has type bool If the operands have generic type int the result also has type int in this case the operation is a bitwise operation Note that precedence of the operators is what is usually expected for the logical operations Due to the arbitrary precision of integer expressions care must be taken when bitwise operations are applied see Section 1 6 2 2 1 6 1 4 Concatenation The operator denotes array concatenation It requires that b
13. the simulator will stop at the next statement of the process that made the call Hence this acts more or less as a permanent breakpoint procedure print This procedure can be passed any number of arguments It prints its argument values on the standard output followed by a newline E g x 5 y red print x and y are x y results in q 0 r gt x and y are 5 red where process instance q 0 r executed the print call procedure show This procedure prints its arguments with their values show x 1l y prints q 0 r gt example chp 7 3 x 1 6 y red Note that it also indicates the location of the call procedure warning procedure error These cause a warning and error respectively with the argument values as message in the same way as print procedure assert cond bool Causes an error if the condition is false There is also a built in type st ring which is an array of 0 127 i e an array of ascii values However since no array bounds are specified you cannot index variables of this type It is useful for some debugging routines Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 28 chpsim 1 2 2 4 Standard I O There is a standard module st dio chp that defines procedures for reading and writing files This module must be imported with requires to use these procedures Obviously this module is intended for testing and debugging onl
14. val res parameters get their initial value assigned from the correspond ing arguments at the very beginning of the call At the very end of the call the final values of res and valres parameters are copied to the corresponding arguments of the call In a hardware implementation this mechanism easily translates to receiving and sending initial and final values During the call the parameters are local variables of the routine note that res parameters are not initialized Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 10 chpsim 1 2 procedure g val p int valres q int res r int CHP q q Pp p q r p 1 Suppose we have x 3 and i 1 then call g x i a i Afterward x 3 i 4 and a 1 5 Note that the location of a i was determined before the call so that a 1 is modified rather than a 4 The type requirements for parameter passing are the same as for assignment In addition the arguments for res and valres parameters must be values writable locations It is an error to pass the same location for two result parameters in the same call E g with the above example g x i i would be wrong 1 4 2 Functions function_definition function identifier value_parameterse type chp_body A function has a return type and is called as part of an expression The parameters of functions are always val parameters Inside the function the function name acts like a res parameter
15. with optional terminating semi colon There are also iteMseries opt etc denoting zero or more items 1 1 Source File source _file required moduleseries opt global_definitionseries opt global_definition exportop definition definition type_definition const_definition function_definition procedure definition process_definition field_definition O ces aeaa ces The source can be distributed over multiple source files called modules A definition defines the meaning of a name If the definition is marked with export the name is visible outside its own module if that module is imported Exporting a name is necessary if you want to refer to that name in a different module you do not need to export objects that you do not refer to by name E g export type abc array 0 10 of pqr exports the name abc but not pqr It is not necessary to export pqr in order to access elements of an array of type abc Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 6 chpsim 1 2 1 1 1 Importing modules required_module requires string_literal js The string_literal is a file name denoting a module that should be imported There is no default file name extension but there is a search path see I in Section 2 1 Importing a module makes the exported names of that module visible However if multiple imported modules export the same name that name will not be visible Imported names are overridden by
16. a port of the current process The second form identifies a port of an instantiated process For data ports if both connection_points have the same form they must be ports with opposite directions one input one output However if one connection point has the first form and the other the second form both must have the same direction The data types of connected ports must be compatible Using a port of the current process indicates a pass through the port is not used for direct communication but instead is merely a wire between two other ports The current implementation does not perform run time range checks on the data type of a pass through port only on ports that are actually used in communication actions Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 21 1 8 Lexical tokens The description of lexical tokens is slightly informal A token may not contain white space unless explicitly allowed In some cases tokens must be separated by white space to avoid ambiguity 1 8 1 Comments comment ie ANY series opt xj l any except linebreadkseries opt linebreak A comment of the first form cannot contain 1 8 2 Integers integer_literal decimal fl Ox D OX f hexdigit _ series fl Ob OB binarydigit _ series I decimal baseddigit _ series decimal decimal_digit decimaldigit _ series opt Digits gt 9 are a z case insensitive Integers can
17. chpsim A Simulator and Debugger for the CHP Language User Manual 2002 12 18 chpsim 1 2 Marcel van der Goot for the Caltech Asynchronous VLSI Group Copyright 2002 Caltech All rights reserved chpsim 1 2 Language 1 1 Source File 1 1 1 N2 eee ee er ee ee er ee ee eee eee ee ey ere ee ee eee ee eT Te 1 3 Constants 1 4 Routines 1 4 1 1 4 2 1 4 3 1 4 4 1 4 5 1 4 6 1 5 Statements 1 5 1 1 5 2 1 5 3 1 5 4 1 5 5 1 6 Expressions 1 6 1 1 6 1 1 1 6 1 2 1 6 1 3 1 6 1 4 1 6 2 1 6 2 1 1 6 2 2 1 6 2 3 1 6 3 1 6 3 1 1 6 3 2 1 6 3 3 1 6 4 1 6 4 1 1 6 4 2 Contents Importing modules Boolean type Integer types Integer fields Symbol types Array types Record types Parameter passing Functions Procedures Processes Routine body Scope and order of definition Assignment Communication Repetition Selection Procedure call Binary expressions Arithmetic operators Comparison Logical and bitwise operators Concatenation Prefix expressions Arithmetic operators Logical and bitwise operator Probe Postfix expressions Indexing of arrays Indexing of integers Accessing fields of records Atoms Array constructor Record constructor Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group N ODA o0 o0 o0 wo N N 1 7 1 8 2 1 2 2 2 3 2 4 chpsim 1 2 1 6 4 3 Function call 18 1 6 5 Literals 18 Meta processes 5 5 c6550innsahe tescdnaee de
18. contain underscores but not as first character The notation allows for integers in any base 1 lt base lt 26 1 8 3 Identifiers identifier letter _ letter digit I _ series opt Identifiers may not be keywords they are case sensitive 1 8 4 Keywords Keywords are case insensitive 1 8 5 Characters and strings character literal char_character printable character char_character printable_character except A backslash is used as escape character The following escapes are recognized Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 22 chpsim 1 2 A printable_character is any character in the ASCII range 0x20 through 0x7E i e a space character or a character that involves ink when printing string literal string_character printable character series string character printable_character except and Escapes for strings are the same as for characters Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 23 Simulation 2 1 Command line arguments The chpsim program takes the following command line arguments source file The top level module Only one source file is specified on the command line other modules are read based on requires clauses main process The execution starts with one instance of this process This must be a process without meta parameters and port parameters If no main opt
19. dbed obeca nada hese aebons neruu rruaren 19 1 7 1 Process instances 19 1 7 2 Meta parameters 20 1 7 3 Connecting processes 20 Lexical tokens 2525 oti at tiie Dane Mae EEE TEN OEE E E E oe de EE 21 1 8 1 Comments 21 1 8 2 Integers 21 1 8 3 Identifiers 21 1 8 4 Keywords 21 1 8 5 Characters and strings 21 SINUBAUION ps chncesdensnedewkenden DCAOva en eeRedeentedeKd eeake sued eas vaneaewacds 23 Command line arguments 0 0000 000 ccc ccc eee e enna aes 23 Exec ti i 5 siete ohh a ea ae ahs oe aa aca a away ed sehen onus ae aS aa aa D 24 2 2 1 The current statement 24 2 2 2 Steps 24 2 2 2 1 Execution of functions 25 2 2 3 Breakpoints 25 2 2 4 Tracing 26 2 2 5 Inspecting the state 26 2 2 6 Other commands 26 Built in procedures 5 05552 2200ts aesde ne ec Olis ie ceteneerayene ds eedenun cas 26 Standard VO e a kee he eg a ee ne ee Pee 28 Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 5 Language Words in italics denote non terminals or non literal terminals words and symbols in typewriter font denote keywords and literal symbols Choices are separated by bar symbols braces are used for grouping is for grouping is a literal brace The following subscripts are used iteMopt an optional item it Mseries One or more items item list one or more items separated by commas it Mseq one or more items separated by semi colons iteMtseq sequence
20. e record record fieldjseq Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 9 record field identifier tist type The field names are local to each specific record_type The generic type of a specific record type is obtained by omitting the field names and replacing each field type by its generic type For example var a record x y byte var b record p q 100 100 var c record x y z byte Both a and b have the same generic type namely record int int but c does not Assignment of record types requires that each of the field assignments is valid The field names are always accessed through an object of the record type hence they need not be exported 1 3 Constants const_definition const identifier type op initializer initializer const_expr If the type is specified the initializer must be a value of that type otherwise the generic type of the constant is determined directly from the initializer 1 4 Routines The term routine refers to functions procedures and processes 1 4 1 Parameter passing value_parameter Vvalop identifier tist type result_parameter res identifier ist type valres identifier ist type The term parameter refers to formal parameters argument refers to actual parameters The parameter passing mechanism for functions and procedures is value result a k a copy restore passing val and
21. e cycle A module should not import itself Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 7 1 2 Types type_definition type identifier type type integer_type symbol_type array_type record_type generic_type identifier O ao es es eaa generic_type bool J int symbol An identifier used as type must have been defined with a type definition As a special case if the type in an exported type definition is a symbol type Section 1 2 3 the symbol literals are exported as well The language distinguishes between generic types and specific types each specific type can be reduced to a generic type Typically variables have specific types whereas expressions have only generic types When types need to match such as for an assignment it is sufficient if the generic types are equal hence the typing is weak Matching of types can be verified at compile time However each variable may only hold values that belong to its specific type the simulator uses run time checks to verify this condition We use the word type when the context makes clear whether we are referring to generic or specific types 1 2 1 Boolean type The generic bool type is an exception in that there are no specific types Values of bool type are usually produced by comparisons but you may declare variables of type bool as well The bool type has only two values true and false 1 2 2 Integer types inte
22. ers The generic type for all symbol types is symbol Since all symbol values belong to the generic type they are identified only by their name if types color and fruit both have an orange value these values are identical The first occurrence of a name in a symbol_type declares the name as a symbol literal subsequent occurrences in the same scope do not count as declarations Within a single symbol_type each name should occur only once To export symbol literals the symbol_type must be given a name with an exported type definition Section 1 2 1 2 4 Array types array_type array const_range jis of type Having multiple ranges is merely a short hand for nested array types the two types array 1 10 0 5 of byte array 1 10 of array 0 5 of byte describe exactly the same specific type Internally the simulator always uses the latter form The generic type of a specific array type is obtained by omitting the bounds and replacing the element type by its generic type For example var a array 1 10 of byte var b array 0 5 of 100 100 var c array 1 10 of red green blue Arrays a and b have the same generic type namely array of int but c does not When an array value is assigned to an array variable the number of elements must be equal and the assignment of each individual element must be valid Hence a b can never be correct but b a i j may be correct 1 2 5 Record types record_typ
23. ger_type const_range const_range const_expr const_expr integer_type describes a specific type The two expressions denote lower and upper bounds the lower bound must come first The corresponding generic type is the arbitrary precision type int which is used for all integer expression evaluation Any integer expression can be assigned to any integer variable provided that the value lies within the bounds of the variable s specific type Note that there is no automatic truncation of values It is possible to declare variables or parameters of the generic int type This is not recom mended for code that describes hardware but may be useful when defining generic functions such as is_even Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 8 chpsim 1 2 1 2 2 1 Integer fields field_definition field identifier const range This syntax gives a name to the specified range of bits In this case the higher bound may come first Note that the field name is not tied to a particular integer type it can be used with any integer value See Sections 1 6 3 3 and 1 6 3 2 1 2 3 Symbol types symbol_type identifier tist A symbol type consists of a set of symbol literals which are just names For instance type color red orange yellow green blue purple Unlike enumeration types in some languages there is no ordering among symbol literals nor is there an implied mapping to integ
24. hat can only occur in one type of process and not in the other The main difference is with respect to execution The simulator starts by executing meta processes which have as goal to create the graph of CHP processes this is the instantiation phase If meta process P instantiates process Q which may be a meta process itself then Q does not start executing until P has terminated If Q is a CHP process then Q does not start executing until all meta processes have terminated The instantiation phase ends when all meta processes have terminated Once that happens the execution phase starts by executing all instantiated CHP processes in parallel The CHP processes model the actual hardware the meta processes just serve to describe the hardware configuration The parallel_statement in a meta_body has the same form as a regular parallel_statement except that statement excludes communications and is extended as follows Statement meta_binding connection Furthermore a meta process may not contain any probes 1 7 1 Process instances meta_declaration instance identifier ist process_type I declaration process_type identifier array const_range jj Of process_type Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 20 chpsim 1 2 An instance declaration instantiates one or more processes The identifier in process type must be the name of a process as defined with process this
25. his case bit 7 of x is the sign bit However if x gt 0 then x 2 7 is larger than 128 not negative because the infinite sequence of 0 bits has not been changed To change the sign you would need to do x 277 1 6 2 3 Probe The operand of the probe prefix operator must be a port The expression returns a bool result t rue if a subsequent communication action on the port will complete The value probe the form of prefix_expr with braces takes a list of ports The bool_expr that follows can refer to the input ports in the list as if they were variables each input port stands for the value that a subsequent communication will receive The value probe is true if the individual probes of the each of the ports is true and the expression evaluates to true Neither form of probe suspends 1 6 3 Postfix expressions postfix_expr atom l array_access I record_access 1 6 3 1 Indexing of arrays array access postfix expr eXxpriist l postfix expr expr expr Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 17 In both cases the postfix_expr must have a specific array type or have generic type int see Section 1 6 3 2 The whole expression is an value if the postfix_expr is an value The expression x 3 4 5 is exactly the same as x 3 4 5 internally the simulator uses the latter form If the postfix_expr has a specific array type with element type 7 then the firs
26. inly useful when you want to print variable values because variables must be in scope but also changes the default focus for the other simulator commands However these commands never affect the actual order of execution the next statement is the original current statement See Section 2 2 5 for more details Commands may be abbreviated usually to a single letter 2 2 2 Steps The simulator repeatedly executes statements or steps until there is a reason to ask for command input The simulator stops at the beginning of the instantiation phase and at the beginning of the execution phase When the simulator is stopped you can enter commands to inspect variables to set breakpoints etc To make the simulation continue you must enter one of the three commands step next or continue An empty command is equivalent to one of these three depending Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 25 on what made the simulator stop if the simulator stopped because of a step or next command that is also the default in all other cases the default is continue The step command tells the simulator to execute one step i e one statement of the current process This is the statement printed before the command prompt For instance step src at example chp 63 17 pin cmnd The current process is src which is about to execute p n Entering step or in this case an empty command allows execu
27. ion is specified the initial process is main I directory Appends the directory to the module search path If module A hasa requires B clause the simulator first looks for B in the directory where it found A If B is not found in that directory the simulator checks each of the directories in the search path in order The search path does not apply to the top level module nor does it apply if B is an absolute path name or starts with or See also the v option e Clears the search path batch By default an interactive session is started as described in Section 2 2 With this option the simulator executes the whole program without stopping for user commands log file A copy of all user commands and simulator output is written to this file When batch is used the default log file is stderr The log file only applies to simulator output not to output generated by the CHP program see the stdout option stdout file o file Specifies the file to use for the print and show procedures described in Section 2 3 and for stdout defined in Section 2 4 The default is the standard output vy Prints version information the search path and the name of each file that is read trace instance Trace this instance in the same way as the t race command of Section 2 2 4 This is useful with the bat ch option you probably also want to use 10g Instance names are described in Section 2 2 they always start with
28. lly write writes its arguments in the same way as the print procedure of Section 2 3 but without the instance name Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group
29. mmunications count as modification of the port If this exclusion rule is violated the effect is undefined Statements separated by semi colons are executed in sequence From the syntax it follows that commas bind tighter than semi colons Braces can be used to alter the binding A skip statement has no effect 1 5 1 Assignment assignment lvalue expr I lvalue l lvalue lvalue postfix_expr An expression is an value if it corresponds to part of a variable In Section 1 6 we indicate which expressions are values An assignment with an symbol requires that both expressions have the same generic type and that the value belongs to the type of the assigned variable The other two forms of assignment require that the value has type boo 1 a sets the boolean to true a sets it to false 1 5 2 Communication communication port_expr l port_expr expr port_expr lvalue l port_expr portexpr port expr lvalue Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group chpsim 1 2 13 port_expr expr The different forms of communication are referred to as sync send receive pass and peek respectively The port_expr must be a port For a sync the port must be a synchronization port for all other communications it must be a data port For a send the port must be an output port and the expression must be valid for the data type of the port For a receive and a peek the port
30. ocess the meta parameters act as constants e g they can be used in type definitions There are two types of processes meta processes and CHP processes Meta processes serve to instantiate other processes eventually resulting in a process graph with only CHP processes Meta processes cannot contain communications Only when the complete process graph has been created does the execution of the CHP program start Meta processes are explained in Section 1 7 1 4 5 Routine body chp_body chp definition declaration series opt parallel_statementseg opt declaration var identifier jj type initializergy Definitions inside a routine body are local to that routine unlike global definitions they cannot be exported Variables are always local to a routine If a variable has an initial value the value must be of the variable s type Unlike for constants a variable s type cannot be omitted 1 4 6 Scope and order of definition All names including symbol literals are in the same name space However there are multiple nested scopes due to the nesting of definitions Scope is always static i e the meaning of a name can be determined at compile time The outermost scope level contains the names exported by imported modules The next scope level is the module source file itself Definitions and declarations inside a body are local to that body Parameters of routines are also local to that routine s body A name can al
31. onstant Section 1 6 4 3 You may observe that such a call is indeed executed only once Procedure calls are statements and are therefore treated like other composite statements they are not atomic 2 2 3 Breakpoints The break command sets a breakpoint Whenever execution reaches a breakpoint the simulator stops to allow command input Breakpoints are associated with a statement in the code not with a particular instance By itself break sets a breakpoint at the current statement The following form of break sets a breakpoint at the statement at or near the indicated position break filename linenumber position Only the line number is required If a file name is specified it must be between quotes If a position on the line is specified it must be preceded by a colon This third form of break sets a breakpoint at the beginning of the specified routine a process procedure or function break filename routine Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 26 chpsim 1 2 Again the file name is optional If the routine is not a top level routine you can use a dot to construct a hierarchical name use break g f to stop at function f which is declared inside procedure g A file name need only be specified if otherwise the top level routine name is not unique To remove a breakpoint use the clear command when stopped at the breakpoint There is no command to remove a breakpoint that the simula
32. oth operands have the same generic array type the type of the result is that generic array type 1 6 2 Prefix expressions prefix_expr postfix_expr I port_exprijs bool expr prefix_operator prefix_expr Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 16 chpsim 1 2 prefix_operator I I I A prefix expression is not an value 1 6 2 1 Arithmetic operators The and operators require that their operand has generic type int which is also the result type 1 6 2 2 Logical and bitwise operator The operator can be applied to a bool operand in which case it denotes negation and yields a bool result It may also be applied to an operand with generic type int in which case it is applied bitwise resulting in the one s complement operation the result type is int Because int has arbitrary precision care must be taken when bitwise operations are applied For the purpose of bitwise operations an integer is considered as an infinite array of Os and 1s using the standard 2 s complement notation Consequently there is always an infinite number of equal sign bits This means that the operator always changes the sign of an integer While this is sound since by definition x x 1 it may be unexpected if you intended a number to be an unsigned integer For example 0 1 The binary bitwise operators likewise require care with the sign bits Consider var x 128 127 In t
33. t form of ar ray_access has result type T The second form sometimes called a slice has as result type the generic type of the postfix_expr Note that you can only index an array with a specific type i e an array with known bounds Hence x 1 4 2 is not a valid expression The indices must be within the bounds of the array For a slice the smallest index must come first 1 6 3 2 Indexing of integers The same syntax used to index arrays can be used to access bits of an integer In this case the indices must be gt 0 The first form with a single index has result type bool The second form the slice has result type int As explained in Section 1 6 2 2 some care is necessary when treating integers as arrays of bits In particular you should never set the sign bit directly E g var x 128 127 x 7 true If x was gt 0 then the assignment makes x gt 128 not negative because the infinite sequence of 0 sign bits has not been changed The following procedure sets the sign bit correctly set sign bit x pos to b procedure set_sign valres x int pos int b bool CHP Col b gt x DE Re The value of a slice is obtained by treating the specified bits as an unsigned integer Hence with the above x x x 0 7 is unsafe because the result has range 0 255 When taking a slice of an integer it is allowed to put the largest index first 1 6 3 3 Accessing fields of records record_access postfix expr
34. tion of p n and forces a stop at the next statement of src The step command refers to the current process only between the current step and the next stop there may be multiple execution steps of other processes The next command is nearly the same as the step command but it treats function and procedure calls as a single step Le if the current statement is a procedure call next will stop at the statement after the call whereas st ep will stop at the first statement of the called procedure The step and next commands can take an instance name as argument In that case the simulator will stop when it reaches the next statement of that process instance The continue command continues execution until there is reason to stop again such as a breakpoint 2 2 2 1 Execution of functions Since expressions are always part of a statement execution of a statement as a single step implies that expression evaluation is atomic However this poses a problem for function evaluation a function call is part of an expression hence atomic yet its evaluation consists of multiple statements The simulator solves this by executing the function in isolation while executing the function it ignores all other threads until the function has finished Since functions do not interact with other threads their atomicity is actually a non issue it is mentioned only because it can be observed in the simulator Function calls with constant arguments are themselves c
35. tor is not stopped at 2 2 4 Tracing When a process instance is traced the simulator prints every statement executed by that instance without stopping unless there is another reason to stop trace by itself starts tracing the current process instance If an instance name is specified that instance will be traced To stop tracing use clear trace optionally followed by an instance name clear followed by an instance name stops tracing and also cancels a pending step or next for that process i e execution will not stop when the next statement of that process is reached 2 2 5 Inspecting the state The where command prints the current call stack i e the sequence of nested procedure and function calls that led to the current statement You can move the focus up or down this stack with the up and down commands both take an optional number of steps as argument The up direction is towards the caller Moving the focus is useful when you want to print variables because only variables of the current routine are visible You can shift the focus to a different process with the view command Without argument this simply prints the current statement Again this is useful if you want to print variables of that process As mentioned before changing the focus changes the default process for commands like step however it does not change the actual scheduling of statements The print command by itself shows all existing threads print
36. ways be redefined in a nested scope hiding the original meaning of the name Each name may be defined or declared only once in a particular scope except for the names exported by imported modules In case of the latter if different modules export the same name neither meaning of the name is visible As explained in Section 1 2 3 all symbol literals belong to the same generic type Symbol literals are only declared the first time they are encountered in a scope Most names are visible in their own scope and in nested scopes if they have not been redefined However to avoid shared variables variables must always be local to the routine that uses them Routines can be defined in any order but all other names must be defined or declared before they are used However if a process definition and instantiation occur at the same scope level then the definition must precede the instantiation Written by Marcel van der Goot for the Caltech Asynchronous VLSI Group 12 chpsim 1 2 1 5 Statements parallel_statement Statement list statement skip assignment communication loop_statement selection_statement procedure_call parallel_statementyseq feces cs cs ees ces A Ml Statements separated by commas are executed in parallel A variable that is only read may be read by multiple statements in parallel However a variable that is modified may be accessed by only one of a group of parallel statements With respect to this rule co
37. y type file const stdin file const stdout file type file_err ok eof no_int Opening and closing of files is done with procedure fopen res f file name string mode string procedure fclose f file The mode argument is the same as for the fopen function in C In particular r opens the file for reading w opens the file for writing erasing the existing contents Reading is done with procedure read_byte f file res x 0 255 res err file_err procedure read_int f file res x int res err file_err read_byte reads a single byte character If successful it sets err to ok otherwise it sets err to eof and x to 0 read_int skips white space then reads an integer written in the standard CHP notation Section 1 8 2 The integer may be immediately preceded by a single minus sign If no digit is found err is set to no_int and x to 0 At the end of the file err is set to eof Writing is done with procedure write_byte f file x 0 255 procedure write_string f file x string procedure write_int f file x int base 2 36 procedure write f file write _byte writes a single byte character write string writes a sequence of characters stopping if a 0 character is encountered the 0 is optional write _int writes an integer in the specified base Decimal integers are written without base hexadecimal is written with Ox and all others are written with the base notation Fina
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