PDF - Forth, Inc.
Contents
1. Vectoring Arrays of Structures Rieks Joosten State University of Utrecht Laboratory for Experimental Physics Princetonplein 5 Utrecht the Netherlands Hans Nieuwenhuyzen Sterrewacht Sonnenborgh Zonneburg 2 Utrecht the Netherlands Abstract Writing a program module requires the specification of the interface between this and other program modules or the operating environment Since modularity implies that you can replace one module by another a mechanism is needed to switch the definitions datastructures that make up the program module interface In this paper a general way of switching the action of a set of Forth datastructures which can be thought of as a program module interface is presented Introduction It is shown that software can be designed in a structured way e g for switching hardware oriented drivers Switching drivers can now be done in a very general and safe way A general framework is defined which is the virtual interface between the hardware driver and user software When an actual driver is attached to this framework its routines fields will be called by the user program through the VI Virtual Interface Drivers generally need some special action before they can be used e g initialization of hardware or before they can be de assigned e g turning off power The syntax allows such actions to be specified when defining the actual drivers An example is given of a character2. Figure 2 After typing DA the AMSI structure of the DA module has been attached to the VMSI struct 38 The Journal of Forth Application and Research Volume 1 Number 2 If now the word DB is typed the AMSI structure of the DA mass storage module is de coupled from the V MSI structure of the block systems module Then the AMSI structure of the DB mass storage module is attached to the VMSI structure of the block systems module see Fig 3 At this moment definitions from the block system will use the routines of the DB module which means that blocks are read from and written to the DB device Figure 3 After typing DB the AMSI structure of the DA module is de coupled The AMSI structure of module DB is attached to the VMSI structure 2 Modular Interfaces We will now extend the example from the previous section and introduce a general syntax for interfacing two modules One of these is the master module it uses routines from the other module called the slave module The master module contains the structure the Virtual Interface VI structure that specifies what routines should be in the slave module and what these routines should do The slave module also contains a structure the Actual Interface Al structure that takes care of the correct attaching of the slave to the master module Note that VI structure is the general structure of which the VMSI structure was a specific example the same holds f
3. EXEC is the cfa of the routine that acts on data in the field FIELDS of the current actual structure the address of where this data can be found should be on the top of the stack AINIT is the cfa of the routine that initializes a field of type lt SWORD gt given the address of the field on the stack and an initialization string in the input buffer 46 The Journal of Forth Application and Research Volume 1 Number 2 AINIT is the cfa of the routine that initializes a field of type lt SWORD gt given the address of the field on top of the stack and one or more number s below this address LENGTH is the length of a field of type lt SWORD gt 8 Example of the Use of the Structures This section contains an example of the use of the technique described Although designed for interfacing purposes especially in conjunction with peripheral drivers this technique may turn out to be useful in other applications Definition of the Virtual 1 O Device This example describes character I O In Forth the terminal character I O is organized using the words KEY and EMIT Two additional helpful routines are 72KEY and EMIT KEY leaves a boolean telling whether a character is available from the current input device and EMIT leaves a boolean telling whether the current output device can accept a character For this example the routine CURDEV prints the name of the current I O device The definition of such an I O device is then descr
4. Parameter Field Address is on top of the stack ORPHAN ONLY WHILE EXECUTING ORPHAN gt lt ADDR gt lt SECURITY gt starts compilation of a colon routine as but without a name HEADER Asit has no name its code field address is left on the top of the stack below the security code This code may be executed by EXECUTE
5. a senior research fellow at the University and promotes Forth for interactive environments Dr Nieuwenhuyzen is currently teaching courses in digital data processing including data transport data base access and processing for applications in remote sensing astronomy high energy physics and medicine Mr Rieks Joosten attended the State University of Utrecht concentrating in physics and is changing his concentration to informatiks He is currently serving his military duty in Holland Mr Joosten is interested in operating system kernals and continues to use Forth and metaForth to develop easily generated user friendly systems 52 The Journal of Forth Application and Research Volume Number 2 Appendix A Definition of Non Standard Words Used The Forth system that supports the implementation of the described structures is not a 79 standard system This appendix describes any discrepancies between the 79 standard system and the words and concepts that are used in the examples Some words refer to separate papers The Case statement The CASE statement used requires the following syntax lt NR l gt lt NR 2 gt CASE lt EQUAL PART gt ELSE lt NOT EQUAL PART gt THEN or lt NR I1 gt lt NR 2 gt CASE lt EQUAL PART gt THEN where the code compiled by CASE checks the top two numbers on the stack for equality If the two top numbers are equal both are dropped and the lt EQUAL PART gt will be executed after which e
6. cfa of INIT routine ORPHAN HERE SWAP push cfa of IN1F routine amp WORD C I ALLOT ORPHAN DUP push cfa of DO routine IF COUNT TYPE THEN SWORD STEXT Create a new word of type SWORD with name STEXT The word ORPHAN is not standard see Appendix A for its explanation 42 The Journal of Forth Application and Research Volume 1 Number 2 6 Implementation The implementation of the described structures has been done in FysForth vsn 0 3 This Forth system uses the TO concept 1 and some defining words which also solve some problems with forgetting 2 For system dependencies we refer to the FysForth vsns 0 2 0 3 User Manual 3 The following code implements the described structures Some routines use the reference word set as appended to the 79 standard Appendix A of this paper contains a description of non standard words RIX 19830301 HEX Helpvariables and helproutines 0 VALUE VIRT ACT 0 VALUE VADDR 0 VALUE STRUCLEN SINIS 0 TO VIRT ACT 0 TO VADDR 0 TO STRUCLEN VIRT ACT VIRT ACT lt gt IF CR SYNTAX ERROR VIRT ACT VIRT ACT SINIS ABORT THEN EXEC EXECUTE Defining word for general virtual interface DO gt BUILD gt HERE TO VADDR 1 TO VIRT ACT 0 TO STRUCLEN 0 0 PRE BUILD gt 0 VIRT ACT DEFWORD gt VIRTUAL Defining word for Fields in general interfaces DO gt DUP DUP IF OVER 2 SWAP 4 EXEC ELSE NFA COUNT
7. contents of a named field in an actual structure 4 Syntax and Semantics of the Actual Interface Structures ACTUAL lt virtstruct gt lt actuainame gt Start the structure OPEN gt lt open routine gt Init open action CLOSE gt lt close routine gt Init close action lt m gt lt p gt INIT lt fld name gt lt texi gt lt q gt lt number gt INIT lt fieldname gt Initialization of some of the defined fields END End of structure where is optional lt word gt is a symbolic name capital letters are existing names lt n gt denotes that occurs lt n gt times lt virtstruct gt is the name of the routine that contains the general specification of structures of its type see the definition of lt virtstruct gt on the previous page lt actualname gt is the name of the routine that will close the current structure of type lt virtstruct gt i e finish make itself current and open the current structure of type lt virtstruct gt i e itself OPEN is the routine that assigns an lt open routine gt which is the name of a Forth routine to the general open routine for the actual structure lt actualname gt The open routine for an actual structure is executed as soon as that actual structure is made the current one Such routines handle the needed initialization CLOSE gt is the routine that assigns a lt close routine gt to the gener
8. work is provided the interface between the module of his program and other defined modules Therefore modules have to be specified e g what actions they can take and the interfaces between modules have to be specified since modules must be able to communicate with other modules Forth system software includes chunks of software that could readily be written in terms of modules As an example let us see how one could write the block words using program modules A block system contains among others the following words BLOCK BUFFER and SAVE BUFFERS These words use some kind of mass storage organization that is not important to a user as long as he can efficiently use all the mass storage media that he wants to use he may not be interested in the organization of blocks on the mass storage medium When a system has to use different devices at the same time there are some problems like How does the block system know which mass storage device is in use and How does it know how to read from or write to this device Here modular programming can help you Assume a mass storage program module that contains definitions that allow you to read a block from a mass storage device write a block to it etc Now some way to link both modules is needed the module interface The module interface contains a specification of the definitions the block system program module wants to use but does not have available The m
9. 1 O system and a possible implementation is given based on FysForth vsn 0 3 The technique can be used whenever a vector of routines is used and when the complete execution vector needs to be switched In section we describe a mechanism for interfacing between modules using a block system built on different mass storage drivers as an example In the second section we will deal in a more general way with problems that may occur showing some examples of the syntax for building the structures that are introduced in the first chapter Sections 3 through 5 deal with the syntax and semantics of all relevant structures in detail The implementation used is given in section 6 section 7 shows the internal structure of the words that are built After several examples in section 8 we discuss performance and tradeoffs For those who are not familiar with the system on which the described mechanism is implemented Appendix A gives the deviations from the used system with respect to the Forth 79 Standard The Journal of Forth Application and Research Vol 1 Number 2 Dec 1983 35 36 The Journal of Forth Application and Research Volume 1 Number 2 I Modular Programming Modular programming is a programming technique that allows multiple programmers to work on the same job at the same time This is achieved by assigning each programmer a part of the job called a module A detailed specification of the constraints to which the programmer has to
10. 3F AND STYPE NOT ASSIGNED ABORT THEN BUILD gt VADDR STRUCLEN DUP 6 TO STRUCLEN PRE BUILD gt 1 VIRT ACT DEFWORD gt FIELD Set hexadecimal base See 1 for VALUE Generate VALUEs Reset the values Test for the wanted structure type ABORT if the wrong structure is found See 2 for DO gt BUILD gt PRE BUILD gt etc Pointer to current struct Total structure length Check validity before building the Virtual lt PFA gt lt CURSTRUCT gt lt PFA gt lt CURSTRUCT OFFSET gt lt CURSTRUCT OFFSET gt is on top of the stack Abort when not assigned Adjust STRUCLEN with the length field of type lt SWORD gt Check validity before building the Field Vectoring Arrays of Structures Defining word for real actual interfaces FORGET gt DUP gt S 6 S IF S 4 EXEC 0S THEN S DO gt DUP gt S DUP IF 2 EXEC THEN S DUP 6 SWAP S gt 2 EXEC Save pfa of actual Is this actual current Close the actual De assign the virtual Clean up system stack Close current struc ture if it was current then switch the actual to become the current structure BUILD gt DUP Pointer to virt struct 0 Addr s of the default 0 real open close words HERE TO VADDR Save the field addr 2 Erase and allocate mem HERE OVER ERASE for the fields ALLOT 2 TO VIRT ACT Set actual mode PRE BUILD gt 0 VIRT ACT Check validity before building the Ac
11. ATE gt lt RELOCATE PART gt DO gt lt DO PART gt t DOCODE gt lt DO PART gt BUILD gt lt BUILD PART gt PRE BUILD gt lt PRE BUILD PART gt DEFWORD gt lt NAME gt Vectoring Arrays of Structures 53 where is optional lt word gt is a symbolic name capital letters are existing names lt n gt denotes that occurs lt n gt times lt I gt lt 2 gt lt 3 gt lt m gt area set of items lt I gt through lt m gt of which one is required lt NAME gt will be the name of a new defining word lt PRE BUILD PART gt are those routines that are executed before a header will be built lt BUILD PART gt are the words that create a parameter field for a word of type lt NAME gt lt DO PART gt are the words that execute a routine of type lt NAME gt with the parameter field address of the called routine on the stack lt RELOCATE PART gt would be the words that relocate a routine of type lt NAME gt with the parameter field address of the called routine on the stack lt FORGET PART gt are the words that execute before a routine of type lt NAME gt will be forgotten The forget part will have the parameter field of the routine to be forgotten on the stack The minimum set consists of DO gt ews DOCODE gt BUILD gt ress or BUILD gt DEFWORD gt ab DEFWORD gt The System Stack A special stack system stack is implemented
12. INIT KEY TT2KEY executes when the actual TT INIT KEY TT KEY is de assigned Initialize INIT EMIT TT2EMIT the field that contains the INIT EMIT TT EMIT name of the driver and the fields of type SEXEC END Terminate initialization Defining Other Actuals of Type I O DEVICE Other types of actual 1 O DEVICE drivers can be defined once we know how the VIRTUAL I O DEVICE is defined Assume that the routines INIT PRINTER PORT LP EMIT and LP EMIT have been defined to initialize the printer i o to see whether a character can be written to the printer and to output a character to the printer Printer driver ACTUAL 1 0 DEVICE LP OPEN gt INIT PRINTER PORT INIT CURDEV Line printer INIT KEY 0 INIT KEY ABORT INIT EMIT LP EMIT INIT EMIT LP EMIT END Note that 0 is a regular Forth routine in most systems and therefore can be used as the routine to initialize a field of type SEXEC Analogously a paper tape reader can be defined when the definitions INIT PT READER PT KEY and PT KEY have been defined INIT PT READER initializes the paper tape reader hardware PT KEY and PT KEY performthe 7KEY and KEY action respectively on the paper tape reader Vectoring Arrays of Structures 49 Paper tape reader driver ACTUAL I O DEVICE PT READER OPEN gt INIT PT READER INIT CURDEV Paper Tape Reader INIT KEY PT KEY INIT KEY PT KEY INIT EMIT 0 INIT EMIT ABORT END A sepa
13. KEY TT KEY CFA INIT KEY INIT 2EMIT TT2EMIT TT EMIT CFA INIT EMIT END The only difference between these two terminal drivers is in the definition of TT the one is initialized using INIT while the other is initialized using INIT Internally there is no difference between the two TT s Specification of an Actual Terminal I O Driver which has an Initialization Procedure Assume now that the terminal needs some initialization before it can be used or that the user wants to set this terminal to a known state e g erase the screen Suppose the routine TT OPEN is defined to do this We now write Terminal driver 3 ACTUAL 1 O DEVICE TT Create an actual instance of an 1 O DEVICE driver OPEN gt TT OPEN Assign TT OPEN as the routine that executes when the actual INIT CURDEV Terminal TT is made current INIT KEY TTKEY Init the field that contains INIT KEY TT KEY the name of the driver INIT EMIT TT2EMIT Initialize the fields of type INIT EMIT TT EMIT SEXEC with the appropriate routines END Finish the initialization The sequence OPEN gt TT OPEN initializes the field in the actual structure that contains the execution address of the open routine This means that every time we type TT the routine TT OPEN will be executed and thus initializes whatever is necessary Specification of an Actual Terminal I O Driver which has a Termination Procedure In the same way as for the initialization proce
14. al close routine for the actual structure lt actua name gt The close routine for an actual structure is executed as soon as that actual structure is released from the current structure This can be achieved by assigning another actual structure as the current one or by FORGETing the actual structure that happens to be the current one assuming that FORGET is able to do such see ref 2 Routines such as the lt close routine gt handle finalization INIT initializes the named field lt fld name gt using the string following the fieldname This string should be delimited by quotes Vectoring Arrays of Structures 4 lt number gt symbolizes Forth words and or numbers that put one number on the stack Example 2002 returns a valid number as well as the sequence DEPTH CFA 2 INIT initializes the named field lt fieldname gt using the number on top of the stack 5 Action of the lt WOR D gt s The routines of type lt WORD gt take care of the type of the fields in both virtual and actual structures These routines have to contain information about the length of the field in bytes the execution of the routines assigned to the field lt fieldname gt that will act on the data in that field the initialization procedure INIT on that same field given the data storage address of the field on top of the stack and a text in the inputbuffer the initialization procedure of INIT on that same field giv
15. dules it uses since it only sees the VMSI structure through which it accesses the routines from the currently active AMSI structure Switching the currently active AMSI structure ensures that the block system program will from that moment on use another device Suppose we have the routines DA and DB which will allocate the AMSI structure of the DA or the DB module respectively First after having loaded both the DA and the DB module and the block system program module the VMS from the block system progam module is not attached to either of the AMSI structures see Fig 1 Veen ne ene ee ee nee een eee Ree eee ene nen een e nnn nner set Figure Organization after definition of all modules VMSI and AMSI structures are not attached If at this time you try to use words from the block system an error condition exists because the block system words try to access some mass storage device through the VMSI structure which in its turn is not linked to any AMSI structure the interface is incomplete When the word DA is typed the AMSI structure of the DA mass storage module is attached to the VMSI structure of the block systems module see Fig 2 At this moment executing words from the block system will use the definitions from the DA module which means that blocks are read from and written to the DA device pe cae cere e ee enews meee meee ene ewe neem E E erent a tee et tment wee ten cee n ene m ncn w ene atem enter rte
16. dure a special action is taken when the current is de assigned i e when another I O DEVICE type routine is made current thereby de assigning the previous i o device driver Any special action to be taken before de assigning an actual driver can also be specified Suppose the routine TT CLOSE will take such special de assignment action for the terminal driver We then have 48 The Journal of Forth Application and Research Volume 1 Number 2 Terminal driver 4 ACTUAL I 0O DEVICE TT Create an actual instance of an I O driver CLOSE gt TT CLOSE Assign TT CLOSE as the routine that executes when the actual INIT CURDEV Terminal TT is de assigned INIT KEY TTY KEY Init the field that contains INIT KEY TT KEY the name of the driver INIT EMIT TT2EMIT Initialize the fields of type INIT EMIT TT EMIT EXEC with the appropriate routines END Finish the initialization Specification of an Actual Terminal 1 O Driver which has both an Initialization and a Termination Procedure Of course when the terminal driver needs special action to be taken when it is made current or when it is current and has to be de assigned the following syntax will be used Terminal driver 5 ACTUAL 1 0 DEVICE TT Create an actual instance of an I O driver OPEN gt TT OPEN Assign TT OPEN as the routine CLOSE gt TT CLOSE that executes when the actual TT is made current Assign INIT CURDEV Terminal TT CLOSE as the routine that
17. en a number 2nd on the stack and the data storage address of the field on top of the stack Note that two initialization routines are to be specified An example of the necessity of this is when a STEXT field is to be initialized it is possible that the address of the string that is to be assigned to the STEXT field is on the stack in which case INIT would be used whereas the text can also still in the input buffer in which case INIT will take care for the proper initialization of the TEXT field Creating routines of type lt SWORD gt is done as follows lt length of field gt lt cfa of lt init gt routine gt lt cfa of lt init gt routine gt lt cfa of exec routine gt SWORD lt SWORDname gt where lt length of field gt is the length of the field in bytes lt cfa of lt init gt routine gt is the cfa of the routine that initializes the field starting at the address given on top of the stack using the number 2nd on the stack lt cfa of lt init gt routine gt is the cfa of the routine that initializes the field at the address on top of the stack given a string in the inputstream the string is delimited with quotes lt cfa of exec routine gt is the cfa of the Forth routine that acts on the contents of the address that is on the top of the stack lt SWORDname gt is the name of the new lt SWORD gt Example of creating SWORDS definition of STEXT 2 Length of a STEXT field L CFA push
18. for error recovery reasons The routines that push an integer from the arithmetic stack onto this stack do the reverse action copy the top of the system stack onto the arithmetic stack and delete the top integer from the system stack are the following S S gt gt S S S gt lt INTEGER gt copies the number on top of the system stack to the stack S gt gt lt INTEGER gt pulls the number from the top of the system stack onto the stack lt INTEGER gt gt S gt lt gt transfers an integer from the stack onto the system stack S gt lt gt drops the top integer off the system stack Other Non 79 Standard words Other words used in the article that are not part of the 79 Standard are the following PAIRS CFA NFA ORPHAN 2PAIRS lt INTEGER 1 gt lt INTEGER 2 gt PAIRS gt lt gt checks whether lt INTEGER I gt and lt INTEGER 2 gt are equal If they are not equal PAIRS aborts setting the value PAIR to lt lt bytel gt lt byte2 gt gt where lt bytel gt and lt byte2 gt are the low order bytes of the integers on top of the stack This routine is used to check on program construction errors while using control structures CFA lt PFA gt CFA gt lt CFA gt converts a parameter field address into its code field address 54 The Journal of Forth Application and Research Volume 1 Number 2 NFA lt PFA gt NFA gt lt NFA gt computes the Name Field Address of the routine whose
19. ibed by VIRTUAL I O DEVICE Define a general I O device driver to contain STEXT CURDEV a textfield called CURDEV SEXEC KEY a routine called IKEY SEXEC KEY a routine called KEY SEXEC EMIT a routine called EMIT SEXEC EMIT a routine called EMIT Then terminate the definition END of the virtual I O device driver Definition of an Actual Terminal I O Device It is now possible to use the words CURDEV KEY KEY EMIT and EMIT in new routines It does not matter how the actual routine of KEY etc is accomplished as far as applications are concerned this will only be of importance to the user who wants to specify his own I O device Assume that the following routines are available TT2KEY TT KEY TT2EMIT TT EMIT which doa KEY function a KEY function a EMIT function and an EMIT function respectively for a given terminal A terminal driver is then defined as Terminal driver 1 ACTUAL 1 O DEVICE TT Create an actual instance of an 1 O DEVICE driver in this INIT CURDEV Terminal case a terminal called TT INIT KEY TT2KEY Initialize the textfield to INIT KEY TT KEY contain the drivers name INIT EMIT TT2EMIT Attach the appropriate INIT EMIT TT EMIT routines to the fields of type SEXEC END Finish the initialization Vectoring Arrays of Structures 47 An alternative way to obtain the same actual structure is Terminal driver 2 ACTUAL I O DEVICE TT INIT CURDEYV Terminal TT2KEY CFA INIT 2
20. if this value is 0 no current actual structure has been allocated STRUCLEN is the length of the parameter field of an ACTUAL routine of this VIRTUAL type in bytes Since this length can only be known at the end of the creation of acomplete VIRTUAL structure this field is initialized by the routine END ACTUALSs HEADER AVIRTUAL OPEN i CLOSE FIELDS where AVIRTUAL is the pfa of the virtual structure that was used when this routine was defined using ACTUAL OPEN is the cfa of the routine that is executed immediately after this structure is made the current structure CLOSE is the cfa of the routine that when this structure is the current one is executed immediately before this structure is de assigned as the current one or when this structure is to be forgotten FIELDS is a memory area with length STRUCLEN bytes where STRUCLEN is the contents of the second field of the virtual structure that was used to define this actual structure FIELDs ere ee Tee eee eer ee eer er er er rr eee eee ee er ee eee Te Tree eC Eee rT i HEADER AVIRTUAL OFFSET i SWORD where AVIRTUAL is the pfa of the virtual structure that has been defined the latest OFFSET is the offset in the field FIELDS within the actual structure where this routine finds its data ASWORD is the pfa of the routine of type SWORD that was used to create the routine of type FIELD HEADER AEXEC AINIT AINIT LENGTH where
21. nique is to find the correct set of interfacing routines 3 Syntax and Semantics of the Virtual Interface Structures There are two phases in defining interface structures l define a Virtual Interface VI structure and 2 define an Actual Interface AI structure together with the optional initialization of its fields We define the general syntax of a virtual structure VIRTUAL lt virtstruct gt Start the structure Define the framework lt n gt lt SWORD gt lt fieldname gt Specify the fields in the framework END End of structure 40 The Journal of Forth Application and Research Volume 1 Number 2 where is optional lt word gt is a symbolic name capital letters are existing names lt n gt denotes that occurs lt n gt times lt virtstruct gt is the name of the routine that contains the general specification of structures of its type lt SWORD gt is one of the following types SCONS SVALUE SVAR STEXT SEXEC Note that the words of type lt SWOR D gt create Forth routines that act on the data in the respective field of the current actual structure If there is no currently defined structure an error occurs How the routines act on the data in the current actual structure depends on how they were specified at creation time of lt SWORD gt Additional routines of type lt SWORD gt can always be created lt fieldname gt corresponds to the routine that acts on the
22. odule interface should describe what definitions must be part of the mass storage driver program module Some kind of structure being the equivalent of the module interface description will have to be present in the block system program module so that you can define the whole of this module without having to worry about how the actual mass storage handling words are put together This structure is called the Virtual Mass Storage Interface VMSI structure and contains the specifications of the actions that can be taken by a mass storage driver The driver cannot do anything specific unless actual actions have been assigned to each of the words specified by this structure In the example the following definitions are specified in the VMS structure Definition type Name Description VARIABLE ote da ERRE Saad sa kes Error specifying number CONSTANT L DEV Nr of blocks on the device Or CODE wen 3 eat ak BREAD Read a block from the device zor CODE 32 iseee bis Devens BWRITE Write a block to the device SOF CODE 1 6 Gis ee ee ses RESET es oda os Reset the device Analogously the actual mass storage driver program module has to contain a structure that will enable the correct coupling of the actual mass storage driver program with the block system program module i e the VMSI structure This structure in the actual mass storage driver program module will be called the Actual Mass Storage Inte
23. or the Al and the AMS structures The VI structures of the example of the previous chapter can now be defined We assume here that the routines that are densely printed are available in the Forth system See sections 3 and following for discussion of these words VIRTUAL MS DEVICE SVAR ERR SCONS L DEV SEXEC BREAD SEXEC BWRITE SEXEC RESET END The definition of this V structure specifies that an AI structure of type MS DEVICE will consist of five fields of which the first will act as a variable the second as a constant and the others as an executable Forth routine The Al structures for the mass storage driver program modules DA and DB are defined as follows provided the words used are known to the Forth system Vectoring Arrays of Structures 39 ACTUAL MS DEVICE DA 0 INIT ERR 2002 INIT L DEV DA BREAD CFA INIT BREAD DA BWRITE CFA INIT BWRITE DA RESET CFA INIT RESET END ACTUAL MS DEVICE DB 0 INIT ERR 2002 INIT L DEV DB BREAD CFA INIT BREAD DB BWRITE CFA INIT BWRITE DB RESET CFA INIT RESET END This syntax has been chosen to help in defining the actions Specifying syntax and semantics of words that together make up some concept takes careful analysis of what is going on and what it really is that you want This syntax may seem difficult at first because at first sight it does not resemble Forth However it was defined to do what it has been told to A few situations need caref
24. rate papertape puncher driver can be defined as follows INIT PT PUNCHER initializes the puncher hardware PUNCHER OFF turns the power off from the puncher and PT EMIT and PT EMIT perform the EMIT and EMIT action on the puncher Paper tape puncher driver ACTUAL 1 0 DEVICE PT PUNCHER OPEN gt INIT PT PUNCHER CLOSE gt PUNCHER OFF INIT CURDEV Paper Tape Puncher INIT KEY 0 INIT KEY ABORT INIT EMIT PT PEMIT INIT EMIT PT EMIT END Suppose we want to read from the paper tape unit but also to write to the puncher e g for copying paper tapes Since both the paper tape reader and the paper tape puncher have hardware that has to be initialized we have to write a routine that will initialize both the reader and the puncher hardware INIT PT Create a routine that will INIT PT PUNCHER initialize both the papertape INIT PT READER puncher and reader Now we are in a position to write the paper tape reader puncher I O device driver Paper tape reader puncher driver ACTUAL 1 0 DEVICE PT OPEN gt INIT PT Specify by an OPEN and a CLOSE gt PUNCHER OFF CLOSE action INIT CURDEV Paper Tape Reader Puncher INIT KEY PT PKEY INIT KEY PT KEY INIT 2EMIT PT EMIT INIT EMIT PT EMIT END 50 The Journal of Forth Application and Research Volume 1 Number 2 9 Performance and Tradeoffs Only one pointer has to be changed to switch ACTUALS in this particular implementation which
25. rds NO CR Wrong syntax used Generate a syntax error ABORT message DO gt COMPILE FIELD BUILD gt DO routine INIT routine INIT routine A Length of field in an DEFWORD gt SWORD ACTUAL structure 2 Length of field 2 E CFA INIT routine NO CFA INIT routine CFA SWORD SCONS DO routine 2 Length of field 2 ey CFA INIT routine NO CFA INIT routine EXIT CFA SWORD SVAR DO routine 2 Length of field 2 e CFA INIT routine NO CFA INIT routine EXECTO CFA SWORD SVALUE DO routine 2 Length of field 2 vt CFA INIT routine ORPHAN FIND 0 4 7ERROR CFA SWAP INIT routine EXEC CFA SWORD SEXEC DO routine 2 Length of field 2 a CFA INIT routine ORPHAN HERE SWAP amp WORD C I ALLOT INIT routine ORPHAN DUP IF COUNT TYPE THEN DO routine SWORD STEXT 7 Internal Structure of Words That Are Built This section describes the internal structure of the following word types lt VIRTUAL gt lt ACTUAL gt lt FIELD gt lt WORD gt Note within each type every field is 2 bytes long unless explicitly specified otherwise VIRTUALs HEADER CURSTRUCT STRUCLEN eee ena e eee wee ee eet eee een ee ee eee t ee esc cew een amen tonctbecweececcedeucemewesce Vectoring Arrays of Structures 45 where HEADER is the link field name field and code field of the routine CURSTRUCT is the pfa of the current actual structure
26. rface AMSI structure So we have a VMS and an AMSI that have to work together in actual use together they can be thought of as being the interface between two modules The AMSI and VMSI structures are specific examples of the Al Actual Interface structure and the VI Virtual Interface structure that will be introduced later Suppose we have available a mass storage device called DA and the following definitions DA BREAD DA BWRITE DA RESET that are incorporated inthe AMS structure the routines in the block system module can use them through the VMSI structure Now suppose we have two mass storage devices called DA and DB The documentation that is supplied with these devices gives all the information needed to write the routines that read from write to and reset these devices We also need to create a constant that contains the maximum number of blocks that fit on these devices to create a variable that can be used by the read and write routines to store error conditions into For the purpose of the example we will assume that the above definitions are also available for DB so now we have Vectoring Arrays of Structures 37 DA BREAD DA BWRITE DA RESET and DB BREAD DB BWRITE DB RESET which read a block from write a block to and reset the devices DA and DB respectively Obviously both mass storage driver program modules will have an AMSI structure The block system program module does not know which of the above mo
27. rs Group EFUG item 15 This is one ofa set of papers mailed in April 1977 through the EFUG by H Nieuwenhuyzen Utrecht Observatory the Netherlands and redistributed by R Milkey Kitt Peak National Observatory USA in June 1977 for the U S 5 W Ragsdale A New Syntax for Defining Defining Words FORML Proceedings 1980 Vectoring Arrays of Structures 51 Acknowledgements We want to thank Thea Martin of the lnstitute for Applied Forth Research Inc Rochester Larry Forsley and Carol Pruitt of the Laboratory for Laser Energetics Rochester Ted Bouk and Jerry Spitzner of the Eastman Kodak Company Rochester for having it made possible for one of us Rieks to stay in the United States during the last half of 1982 In this time the first ideas of this Virtual Actual concept were conceived Discussions with several of the above mentioned people gave a good start toward its development We also want to thank Harm Braams and Frans Cornelis for having helped to find the syntax currently used for the described structures and for the time they spent analyzing discussing this concept and its use and for their proposals for enhancements Finally we want to thank Dr James Basile of the Long Island University Greenvale NY for his comments on this paper Manuscript received June 1983 Dr Hans Nieuwenhuyzen receiveda Ph D in astronomy and physics from the State University of Utrecht in Utrecht Holland in 1970 He is
28. se implementations on practical experience Conclusions Advantages of this concept are ease of switching a set of routines ability to define special action before and after the switching possibility to work with virtual definitions ease of writing actual definitions ease of reading source code implying good maintainability possibility to optimize runtime routines within the structures e g by using machine code definitions Disadvantages of this concept are some small overhead in time this overhead is implementation dependent possible existence of problems due to the forward references used in the virtual structures most implementations of Forth systems cannot handle forward references safely FORGETIting such structures can lead to system crashes unless precautions are taken Using the implementation as described in this article problems do not occur FysForth vsn 0 3 which is used for this implementation has been thoroughly tested in this area also see Appendix A References 1 P Bartholdi The To Concept Forth Dimensions January 1979 2 R Joosten and H Nieuwenhuyzen Ideas ona New Forget FORML Proceedings November 1981 3 R Joosten er al FysForth vsns 0 2 0 3 User Manual State University of Utrecht 1983 4 Proposal fora standard Forth interface with mass storage using Forth blocks Svend Lorensen and Jan Vermue Book IV of the European Forth Use
29. therefore can be very fast The consequence however is that words of type FIELD have to fetch the address of the current actual structure add an offset to this address to obtain the address on which the execution routine can act and to fetch the execution address Therefore some extra calculations have to be done due to the extra level of indirection that is introduced High level printer drivers that were written to use this concept were indeed significantly slower Partly this is due to the execution overhead mentioned above The other reason for being slower is that they were written in high level Forth whereas the earlier printer drivers were partly written in machine code After rewriting the execution part of words of type FIELD in machine code the new printer drivers were neither noticeably slower nor faster than the older ones This demonstrates that there need not be a significant time overhead Of course this is implementation dependent An alternative implementation of the structures is that the switching of actuals entails copying the parameter field ofanentire ACTUAL structure toa fixed place in memory This will result ina somewhat slower switch action but the words of type FIELD can execute faster Whether this is actually needed for an application depends on the actual usage of the switch and execution routines Note that this alteration of the implementation does not change the essence of this article We cannot compare the
30. tual COMPILE Put pfa of virtual on the stack DEFWORD gt ACTUAL Routines for initializing fields in an ACTUAL structure OPN CLS 2 VIRT ACT COMPILE CFA SWAP VADDR INT 2 VIRT ACT COMPILE DUP VADDR 6 PAIRS DUP 2 VADDR ROT ROT 4 EXEC OPEN gt 4 OPN CLS CLOSE gt 2 OPN CLS gt INIT 4 INT gt INIT 2 INT Initializes the fields in an actual structure that contain the OPEN and CLOSE routines Get pfa of the lt FIELD gt word Check congruence field actual Calc address to be init ed Calc init exec address Initialize Initialize the OPEN field Initialize the CLOSE field Initialize using a number Initialize using a string The numbers 4 2 4 and 2 that occur in the code of OPEN gt CLOSE gt INIT and INIT respectively are used by OPN CLS and INT to find an address relevant for initialization purposes this is implementation dependent see also the internal structure of ACTUALSs and SWORDS in section 7 of this article Completing the creation of a VIRTUAL Structure or Completing the creation and initialization of an Actual Structure END VIRT ACT DOCASE CASE STRUCLEN VADDR 2 Completing a Virtual ELSE 2 CASE ELSE ABORT ENDCASE SINIS Completing an Actual Abort if neither Reset the helpvalues 44 The Journal of Forth Application and Research Volume 1 Number 2 SWORDs Fields specification wo
31. ul analysis when installing or using this technique If a master module is not attached toa slave module i e there is no currently active Al structure execution of a word in the master module that uses any routine of the slave module generates an error condition Executing the word that attaches the slave module to the master module is essential for correct operation of the module Whenever a slave module is being attached to a master module some initialization of the slave module can take place e g when a disk driver module is attached to a block system module the specified disk drive should be reset This can be done by executing an OPEN routine immediately after the coupling has been completed Analogously before de coupling a slave module from a master module some CLOSE action may take place e g by turning off the power of a device that consumes a lot of power Since there is no reason why a master ora slave module should be loaded before the other this may give rise to forward references The system should take care that any currently active Al structure is properly CLOSED and de coupled when it is forgotten if not execution of routines from the master module may cause a system crash This is a feature that most Forth systems cannot provide However the given implementation on the FysForth system does allow this because it has a specific FORGET action ref 2 The difficult part when using this tech
32. xecution continues behind THEN If the top two numbers are not equal only the number on top of the stack is dropped and the lt NOT EQUAL PART gt is executed if present After this execution continues behind THEN The construction of the DOCASE CASE ELSE ENDCASE statement is as follows lt N gt DOCASE lt NI gt CASE lt lt N gt lt NI gt gt ELSE Nis not equal to lt N1 gt lt N2 gt CASE lt lt N gt lt N2 gt gt ELSE N is not equal to lt N1 gt and lt N2 gt Expansion is limited to the implemented size of the stack lt NN gt CASE lt lt N gt lt NN gt gt ELSE N is not equal to lt NI gt and lt N2 gt and lt NN gt ENDCASE CASE tests if the top 2 numbers are equal If so it drops both numbers and executes the words unti an ELSE or ENDCASE If not it only drops the top number and skips to ELSE or ENDCASE The TO concept The TO concept 1 uses the following routines VALUE TO TO FROM The New Forget Creating Defining Words A new way of creating defining words 2 5 is made possible by the following routines FORGET gt DO gt BUILD gt PRE BUILD gt DEFWORD gt These words allow the building of defining words analogous to those built with CREATE and DOES gt However special action can be taken by FORGET such action is specified for all words of one type at the creation time of the defining word SYNTAX FORGET gt lt FORGET PART gt RELOC
Download Pdf Manuals
Related Search