Preamble ******** Microchip PIC 16F87x microcontrollers are very well suited for a number of tasks. However, the programmer is left with several choices to program them: * Use Microchip MPLab IDE running on Microsoft Windows with the assembly programming language. * Buy a third-party C compiler running on Microsoft Windows. * Use the `gputils' package on a Unix system and program the PIC using the assembly language. * Use the `sdcc' C compiler on a Unix system and program the PIC in C. * Use the `PicForth' Forth compiler on a Unix system and program the PIC in Forth. We do believe that the latest is a very pleasant solution for PIC development, as Forth is particularily suited to embedded systems, and Unix is more user-friendly for the developper. Warning: this manual is a work-in-progress, and is in no way complete. Introduction ************ What is that? ============= This program is a Forth compiler for the Microchip PIC 16F87x family. Why this project? ================= I needed to write some code on a PIC to control a digital model railroad system using the DCC (Digital Control Command) protocol. However, writing it in assembly is error-prone and writing it in C is no fun as C compiled code typically needs a lot of space. So I wrote this compiler, not for the purpose of writing a compiler, but as a tool to write my DCC engine. State of the compiler ===================== The compiler does not aim to be ANS Forth compliant. It has quite a few words already implemented, and I will implement more of them as needed. Of course, you are welcome to contribute some (see below for license information). At this time, many words are missing from standard Forth. For example, I have no multiply operation as I have no use for it at this time and won't spend time to implement things I don't need (remember, Forth is a tool before anything else). License ======= The compiler is released at the moment under the GNU General Public License version 2 (I intend to use the less restrictive BSD license in the future, but as it is based on gforth, I have to sort out those issues with gforth copyright holders). However, the code produced by using this compiler is not tainted by the GPL license at all. You can do whatever you want with it, and I claim absolutely no right on the input or output of this compiler. I encourage to use it for whatever you want. Note that I would really like people to send me their modifications (be they bug fixes or new features) so that I can incorporate them in the next release. Why not use Mary? ================= Mary was a great inspiration source, I even kept some of the names from it. However, no code has been reused, as both Forth do not have the same goal. Credits ======= I would like to thank the following people, in no particular order: * Keith Wootten for his precious examples of how he uses a forth-ish assembler for the PIC and his inspiration for some control structures * Francisco Rodrigo Escobedo Robles for his Mary PIC Forth compiler * Herman Tamas for his suggestions for some word names * Daniel Serpell for his superoptimizer (a program looking for the shortest possible sequences doing a particular job) * Wojciech Zabolotny for his helpful remarks on interrupts and context saving A very short Forth primer ************************* Foreword ======== For a full introduction to the Forth programming language, please have a look at the appropriate section of the Open Directory (maintained by volunteers), at address . Only a small subset of the language will be presented here, sometimes overlooking details. Words ===== The Forth programming language may look unusual to people used to other languages. First of all, the actions to execute are spelled one after each other. The sentence `init mainloop cleanup' will call, in turn, the word `init', the word `mainloop' then the word `cleanup'. To define a new word, the `:' defining word is used, while the `;' word ends the definition. The following code defines a new word `doit' which factors the three words used above: : doit init mainloop cleanup ; After it has been defined, the word `doit' can be called as other words by using its name. A Forth program is a collection of application-specific words. Each word, made of other words, will be used in turn to define new words, until the whole solution is described. Words are similar to subprograms in more conventional programming languages. Any non-blank character can be part of a word name. For example, `\', `^', or `$' are legal characters in a word name, and can even be a word name by themselves. Stack and arguments passing =========================== In Forth, one does not use parenthesis to give arguments to called words. Instead, a stack is used, where the arguments can be pushed and where they can be popped from. The word `+' pops two arguments from the top of the stack and pushes their sum. To push an integer to the top of the stack, one writes its value. The sentence `3 5 +' will push `3' on the stack, then `5', and calls the word `+' which removes `3' and `5' and pushes `8'. Some words do manipulate the stack explicitely. `dup' duplicates the element at the top of the stack, while `drop' removes it. `swap' exchanges the two top elements. The following word that we name `2*' (remember that this name is perfectly valid in Forth) does multiply the top of the stack by two, by adding it to itself: : 2* dup + ; The stack effect of a word is often written as a comment between parenthesis; those comments are ignored by the Forth compiler. The previously defined word could have been written: : 2* ( n -- 2*n ) dup + ; Elements on the stack are represented from left to right (top of the stack). For example, the `-' word which substract the top of the stack from the second element on the stack would have a stack comment looking like `( n1 n2 -- n1-n2 )'. Let's assume that you want to multiply the top of the stack by four. You can define the `4*' word as: : 4* ( n -- 4*n ) dup + dup + ; But remember that you can define your own words from existing words. If you now need a word which multiplies the top of the stack by four, you can use your previously defined `2*' word: : 4* ( n -- 4*n) 2* 2* ; Definitions in Forth tend to be very short. The grouping of common parts in words is called factoring, and leads to very concise machine code. Memory access ============= Two useful words allow you to access memory. `@' gets the content of the memory byte whose address is at the top of the stack and `!' stores, in the memory byte whose address is at the top of the stack, the following element. The code below defines a word `mirror' which mirrors the content of port A into port B (we will later see more practical ways of defining some of the words seen here): : porta 5 ; : portb 6 ; : mirror porta @ portb ! ; Constant and variables ====================== The defining word `constant' allows you to define named constants. Using this word, one can simplify the above example: 5 constant porta 6 constant portb : mirror porta @ portb ! ; The defining word `variable' reserves a byte in the PIC RAM and gives it a name: 5 constant porta variable counter : increment-counter counter @ 1 + counter ! ; : counter-to-porta counter @ porta ! ; Tests ===== Testing in Forth is done using a `if' construct, terminated by a `then', with an optional `else'. Operators such as `<' or `=' can be used, and any non-null value is considered as true. The `abs' word changes the value on top of the stack to its absolute value (note that `abs' and `negate' are in fact already defined by PicForth): : negate 0 swap - ; : abs dup 0 < if negate then ; The word `mirror 'duplicates port A to port B or port C, depending on its argument; `0' for port B, anything else for port C (`porta', `portb' and `portc' constant are already defined in PicForth): : mirror ( n -- ) porta @ swap if portb ! else portc ! then ; Loops ===== Several looping constructs are used in PicForth. The first of them is built upon `begin' and `again', which here calls `do-one-thing' indefinitely: : mainloop begin do-one-thing again ; `while' and `repeat' can add a test in the loop and continue as long as the word `continue?' returns a non-null result: : mainloop begin do-one-thing continue? while repeat ; Note that `while' can be present anywhere between `begin' and `repeat', letting you build elaborate constructs. Also, `until' allows you to wait for a condition. The following word calls `do-one-thing' until `end?' returns a non-null value: : mainloop begin do-one-thing end? until ; The last construct seen here is built around `v-for' and `v-next'. `v-for' takes a (non-included) high bound and a variable address on the stack. The following word `main' calls `do-one-thing' 10 times: variable count : main 10 count v-for do-one-thing count v-next ; Our first PicForth program ************************** The program itself ================== Our first PicForth program will generate a rectangle wave signal on port B0 as fast as possible: 0 pin-b i/o : init i/o >output ; : pulse i/o high i/o low ; : mainloop begin pulse again ; main : program init mainloop ; Line by line explanation ======================== The first line `0 pin-b i/o' defines a new word `i/o' which, when executed, will push two integers `6' (corresponding to portb) and `0' on the stack. This way, instead of writing `portb 0' to manipulate bit 0 of port B you can write `i/o', which is shorter and lets you change it at only one place should you want to change which port is used. The second line uses the PicForth word `>output' which sets the port whose address and bit are on the stack in output mode. This defines a new `init' word which initializes our port B0 as an output. The third line creates a new word `pulse' which uses the PicForth words `high' and `low' to set a pin high or low. As a result, executing the `pulse' word will set the B0 pin high then low, this generating a pulse. The fourth line defines a `mainloop' word which calls `pulse' endlessly, thus generating the rectangle wave signal we want. The last line uses the PicForth word `main'. This word indicates to PicForth that the next word to be defined will be the one to call on reset. The word, called `program' here, calls `init' then `mainloop'. As `mainloop' never returns, the program runs until the end of time (which is usually considered quite a long time). Generated assembly code ======================= The generated code looks like: 0x0000 018A clrf 0x0A 0x0001 280C goto 0x00C ; (init-picforth) 0x0002 0000 nop ; name: init ; max return-stack depth: 0 0x0003 1683 bsf 0x03,5 0x0004 1006 bcf 0x06,0 0x0005 1283 bcf 0x03,5 0x0006 0008 return ; name: pulse ; max return-stack depth: 0 0x0007 1406 bsf 0x06,0 0x0008 1006 bcf 0x06,0 0x0009 0008 return ; name: mainloop ; max return-stack depth: 1 0x000A 2007 call 0x007 ; pulse 0x000B 280A goto 0x00A ; mainloop (rs depth: 1) ; name: (init-picforth) ; max return-stack depth: 0 0x000C 3032 movlw 0x32 0x000D 0084 movwf 0x04 ; name: program ; max return-stack depth: 1 0x000E 2003 call 0x003 ; init 0x000F 280A goto 0x00A ; mainloop (rs depth: 1) An alternate solution ===================== Of course, it is possible to write less factored code for such a simple task, and write instead: 0 pin-b i/o main : program i/o >output begin i/o high i/o low repeat ; In this case, it generates effectively a code which is a bit shorter: 0x0000 018A clrf 0x0A 0x0001 2803 goto 0x003 ; (init-picforth) 0x0002 0000 nop ; name: (init-picforth) ; max return-stack depth: 0 0x0003 3032 movlw 0x32 0x0004 0084 movwf 0x04 ; name: program ; max return-stack depth: 0 0x0005 1683 bsf 0x03,5 0x0006 1006 bcf 0x06,0 0x0007 1283 bcf 0x03,5 0x0008 1406 bsf 0x06,0 0x0009 1006 bcf 0x06,0 0x000A 2808 goto 0x008 ; program + 0x003 However, do not let this short example mislead you. While the code looks more efficient and shorter (and it is), this is generally not true for real-life programs. For example, in a bigger program it would be quite common to have to call `pulse' from other places. Using inlined code ================== It is possible to use inlined code by surrounding the words you want to inline by the `macro' and `target' words: 0 pin-b i/o macro : init i/o >output ; : pulse i/o high i/o low ; : mainloop begin pulse again ; target main : program init mainloop ; While this code is highly factored and easily maintainable, it generates the very same code as the less-factored version above. Compiler documentation ********************** Organisation ============ The stack is indexed by the only indirect register, fsr. The indf register automatically points to the top of stack. The w register is used as a scratch. Attempts to use it to cache the top of stack proved to be inefficient, as we often need a scratch register. Compiling ========= The compiler is hosted on gforth, a free software compiler for Unix systems. The command line to use to compile file `foo.fs' into `foo.hex', and getting a usable map into foo.map is: gforth picforth.fs -e 'include foo.fs file-dump foo.hex map bye' | \ sort -o foo.map Of course, you should automate this in a Makefile, such as the one provided with the compiler. If you install the GNU PIC utils (from http://gputils.sourceforge.net/), then you can read the assembled code by using `gpdasm'. Code ==== The whole code space can be used. However, code generated in the first 2048 words is more efficient than the code generated in the following 2048 words; both are more efficient than the code generated for the remaining words. This is due to the PIC architecture which does not allow to see the code space as a flat zone. Interactive mode ================ By executing gforth picforth.fs -e 'host picquit' (or `make interactive' from a Unix shell), you are dropped into an interactive mode, where you can use the following words to check your code: see ( "name" -- ) Disassemble a word map ( -- ) Print code memory map dis ( -- ) Disassemble the whole code section Literals ======== Hexadecimal literals should be prefixed by a dollar sign `$' to avoid confusion with existing constants (such as `c' for carry bit). This is a strong advice. Default base ============ The default base is hexadecimal. Do not change it before including libraries bundled with the compiler, as they do expect hexadecimal mode. Stack size ========== The default stack size is 16. If you use the multitasker included in `multitasker.fs' (see below), each task gets an additionnal 8 bytes of task-specific stack. You can change the default stack size by using set-stack-size ( n -- ) in interpretation mode before using `main'. Shifting ======== `rlf-tos' and `rrf-tos' respectively shift the top-of-stack left and right, with the carry entering the byte and the outgoing bit entering the carry. `rlf!' and `rrf!' respectively shift the given variable left and right, with the carry entering the byte and the outgoing bit entering the carry. `lshift' and `rshift' used with a constant shift, and `2*' and `2/' do have the last exited bit in the carry. `swapf-tos' will swap the upper and lower nibble of the top-of-stack. Looping ======= There exists a `v-for'/`v-next' structure (v stands for variable): v-for ( n addr -- ) Initialize addr content with n. v-next ( -- ) Decrement addr content. If content is not zero, jump to v-for location. The address has to be located in bank 0. Also, the words `begin', `again', `while', `until' and `repeat' are implemented. Memory ====== You can choose the memory bank that will be used by the memory commands in interpretation mode by using the words `bank0', `bank1', `bank2' and `bank3' (check that it applies to your device first). Those commands do affect the subsequent `create', `variable', `allot', `,' and `here' commands. However, note that you can only access indirectly variables located in bank 0 or in bank 1. Locations in other banks must be accessed using their static addresses. You can define your own memory sections using the words `section', `idata' and `udata'. No check will be made to ensure that those sections do not overlap. Variables ========= Variables are not automatically initialized to zero, as this would waste too much code if it is not needed. If you want a variable explicitely initialized, use `create' and `,' such as in: create attempts 3 , Tables ====== Tables can be created either in RAM (with run-time initialization, which is costly), in program flash memory or in the internal EEPROM. The following words allow you to create tables: table ( "name" -- ) Start a RAM table ftable ( "name" -- ) Start a program flash table eetable ( "name" -- ) Start an EEPROM flash table t, ( n -- ) Add one byte to the table table> ( "b1 .. bn" -- ) Add bytes b1 to bn to the table end-table ( -- ) End table declaration The following code shows a table called `substitutions' and a `substitute' word which takes a byte in area `old-key' and sets it at the right place in area `new-key', according to the `substitutions' table. ftable substitutions table> 14 4 13 1 2 15 11 8 3 10 6 12 5 9 0 7 table> 0 15 7 4 14 2 13 1 12 6 12 11 9 5 3 8 table> 4 1 14 8 13 6 2 11 15 12 9 7 3 10 5 0 table> 15 12 8 2 4 9 1 7 5 11 3 14 10 0 6 13 end-table : substitute ( n -- ) dup old-key + swap substitutions new-key + ! ; Main program ============ A `main' word indicates that the next address is the main program. Use for example: main : main-program ( -- ) (do initialisations) (call mainloop) ; Macros ====== You can switch to macro mode by using the `macro' word. You get back to target mode by using the `target' word. Included files ============== You can include files using `include file' or `needs file' (which prevents from multiple inclusions to happen). Assembler ========= There is a full prefix assembler included. Use `code' and `end-code' to define words written in assembler. `]asm' and `asm[' let you respectively switch to assembler mode and back during the compilation of a Forth word. The `label:' defining word can be used to define a label that will then be used with `goto'. See the `piceeprom.fs' file for an example. Interrupts ========== If you want to use interrupts, use include picisr.fs Two words do respectively save and restore the context around interrupt handling code: isr-save ( -- ) isr-restore-return ( -- ) Note that `isr-save' is called automatically, you do not need to call it explicitely. Also, the word `isr' is provided to notify that the next address is the isr handler. For example, you can write an interrupt handler with: isr : interrupt-handler ( -- ) (interrupt handling code here) isr-restore-return ; Do not forget that the return stack depth is only height. An interrupt can occur at any time unless you mask them or unset the GIE bit. Two facility words that manipulate GIE are also provided: enable-interrupts ( -- ) disable-interrupts ( -- ) You have to dispatch the interrupts and clear the interrupt bits manually before you return from the handler. You can also use the following two words to save the status of the GIE bit and disable interrupts, and to restore the previous GIE status: suspend-interrupts ( -- ) restore-interrupts ( -- ) Versions that do nothing are provided in the default compiler. Useful versions are redefined when using `picisr.fs'. Because of this, include `picisr.fs' as soon as possible, before other files and before using enable-interrupts and disable-interrupts. Other included files may fail to act properly if you don't. Argument passing ================ In Forth, argument passing is done on the stack. However, if you want to transmit the top-of-stack argument in the w register (for example if a word typically takes a constant which is put on the stack just before calling it), you can use the defining word `::' instead of `:'. All calls will automatically use this convention. If you want to return a value in the w register, you can use the word `>w' which loads the top-of-stack into the w register before every exit point. After calling a word which returns its result in the w register, you can call `w>' to put the w register value onto the stack. Bit manipulation ================ To ease bit manipulation, the following words are defined for port p: and! ( n p -- ) logical and with n /and! ( n p -- ) logical and with ~n /and ( a b -- c ) logical and of a and ~b or! ( n p -- ) logical or with n xor! ( n p -- ) logical xor with n invert! ( p -- ) invert content bit-set ( p b -- ) set bit b of p (both have to be constants) bit-clr ( p b -- ) clear bit b of p (both have to be constants) bit-toggle ( p b -- ) toggle bit b of p (both have to be constants) bit-mask ( p b -- m ) put 1<input' or `>output' after a pin defined with `pin-x'. For example, to set the error led port as an output, use: error-led >output Decrementing and incrementing a memory register =============================================== A value in memory can be decremented using the `1 mem -!' sequence. However, as this will be optimized to use the `decf mem,f' which does not position the `c' flag. Usually, this is fine, however, if you want to propagate a carry, you want this flag to be set. To that issue, you can use the `1 >w mem w-!' sequence, which generates `movlw 1; subwf mem,f' and position the carry. Note that propagating the carry while incrementing is easier: the `z' flag is set if needed by the `incf mem,f' instruction generated by the use of the `1 mem +!' sequence. If `z' is set, a carry has been generated. Here is an example to increment a 16 bits value held at location `bar': : inc-16 ( adder -- ) 1 bar 1+ +! z bit-set? if 1 bar +! then ; This will generate the following code: ; name: inc-16 incf 0x34,f btfsc 0x03,2 incf 0x33,f return Watchdog timer ============== The word `clrwdt' is available from Forth to clear the watchdog timer. Reading from or writing to EEPROM ================================= By using include piceeprom.fs you have access to new words allowing you to access the PIC EEPROM: ee@ ( a -- b ) read the content of a and return it ee! ( b a -- ) write b into a Also, in any case, you can store data in EEPROM using those words: eecreate ( "name" -- ) similar as create but in EEPROM space ee, ( b -- ) store byte in EEPROM s" ( " -- eaddr n ) store string in EEPROM l" ( " -- eaddr n ) strore string + character 13 in EEPROM Reading from or writing to flash memory ======================================= Two words allow reading from and writing to the flash memory when the file `picflash.fs' is included with include picflash.fs Those words expect manipulate a 14 bits program memory cell whose 13 bits address is in EEADRH:EEADR. The data is read from or stored to EEDATH:EEDATA. flash-read ( -- ) flash-write ( -- ) If `picisr.fs' has been included before this file, interrupts will be properly disabled around flash writes. The `libstrings.fs' library defines two words useful for working with strings stored in flash memory: c" ( " -- ) Define a packed 7-bits zero-terminated string str-char Get next char of previously encountered c" The following example assumes that you have a `emit' word working, which outputs one character. : print ( -- ) begin str-char dup while emit repeat drop ; : greetings ( -- ) c" Welcome to this PicForth program" print ; It is necessary to include `picflash.fs' before `libstrings.fs'. Map and disassembler code ========================= A map can be generated in interactive mode using the `map' word. Multitasking ============ Two multitasker have been implemented. Priority-based multitasker -------------------------- A basic priority-based cooperative multitasker allows you to concurrently run several indenpendant tasks. Each task should execute in a short time and will be called again next time (the entry point does not change). This looks like a state machine. To use this multitasker, use `include priotasker.fs' in your program. The following words can be used to define tasks (the entry point for the task is the next defined word): task ( prio "name" -- ) Define a new task with priority prio. By default, this task will be active. You can use the `start' and `stop' words to control it. Those words can be used from an interrupt handler. task-cond ( prio "name" -- ) Define a new task with priority prio. By default, this task is inactive. You can enable it by using the `signal' word on it. If you use `signal' N times, then the task will be run exactly N times. `signal' can be used from an interrupt handler. task-idle ( -- ) Define a new task which will be executed inconditionnaly when there is nothing else to do. Such a task can not be stopped. task-set ( bit port prio -- ) Define a new task with priority prio that will be run when bit bit of port port is set. task-clr ( bit port prio -- ) Define a new task with priority prio that will be run when bit bit of port port is clear. Priority 0 is the greatest one, while priority 255 corresponds to the lowest (idle) priority. You should use priority in the range 0-254 for your own tasks. The multitasker is run by using the word `multitasker'. This word takes care of scheduling the highest priority tasks first. It also clears the watchdog once per round. The multitasker looks for all tasks of priority 0 ready to execute. If it find some, it executes them and starts over. If it doesn't, it looks for priority 1 tasks ready to execute. If it find some, it executes them and starts over. If it doesn't, etc. It does this up to priority 255. Since each word is called each time from the beginning, there is no need to maintain task-specific stacks, as the stack has to be considered empty. Basic cooperative multitasker ----------------------------- The basic cooperative multitasker is much simpler. It allows you to relinguish the CPU whenever you want, provided that you are not in the middle of a call (context-switch only occurs during top-level calls). To use this multitasker, use `include multitasker.fs' at the top of your program. The following words are defined: task ( -- ) Create a new task with its own data stack. The task entry point will be the next defined word. yield ( -- ) Relinguish control so that another task gets a chance to execute. multitasker ( -- ) Code for the multitasker program. This word never returns. This multitasker makes no use of the return stack at all. However, each task takes four to six program words for initialization and five program words to resume the task, plus three or four program words per yield instruction. Context-switching takes at most 18 instruction cycles (3.6 microseconds max on a 20MHz PIC, 18 microseconds on a 4MHz PIC), and typically 14. Also, the multitasker takes care of clearing the watchdog timer at each round. Each task needs 3 bytes in RAM to save its context and 8 bytes for its data stack. Libraries ========= Some libraries can be used to enhance your application: * `libnibble.fs' nibbles and characters conversion * `libcmove.fs' implementation of ANS Forth `cmove' word Configuration word ================== The configuration can be configured with the following words: set-fosc ( n -- ) Choose oscillator mode (default: fosc-rc) fosc-lp Low power fosc-xt External oscillator fosc-hs High-speed oscillator fosc-rc RC circuit set-wdte ( flag -- ) Watchdog timer enable (default: true) set-/pwrte ( flag -- ) Power-on timer disable (default: true) set-boden ( flag -- ) Brown-out detect enable (default: true) set-lvp ( flag -- ) Low voltage programming (default: true) set-cpd ( flag -- ) EEPROM protection disable (default: true) set-wrt ( flag -- ) FLASH protection disable (default: true) set-debug ( flag -- ) In-circuit debugger disable (default: true) set-cp ( n -- ) Code protection (default: no-cp) no-cp No protection full-cp Full protection xxxxx Anything you want, with the right bits set (see datasheet) Caveats and limitations ======================= This compiler release suffers from the following known limitations. Note that most of them (if not all) will disappear in subsequent releases. * No interactivity There is no link between the compiler and the target. Optimizations ************* The following optimizations are implemented: Tail recursion ============== Tail recursion is implemented at `exit' and `;' points. : x y z ; generates the following code for word x: call y goto z The sequence `recurse exit' also benefits from tail recursion. Redundant pop/push are removed ============================== For example, the (particularily useless) dup dup drop sequence generates movf 0x00,w decf 0x04,f movwf 0x00 which in fact corresponds to a single `dup'. Also, the following sequence drop 3 generates movlw 0x03 movwf 0x00 while drop 0 gives clrf 0x00 Direct-access and literal variants ================================== Most operations use direct-access and literal variants when possible. The following sequence 9 and generates movlw 0x09 andwf 0x00,f Also, combined with the redundant push/pop eliminations, the following code dup 9 and if ... generates movf 0x00,w andlw 0x09 btfsc 0x03,2 Load, store and operations are mixed ==================================== The following sequence (with `current' and `next' being variables) current @ 1+ 7 and next ! generates movf 0x3B,w addlw 0x01 andlw 0x07 movwf 0x3C Condition inversions ==================== Short (one instruction) `if' actions are transformed into reversed conditions. For example, the following word: \ This word clears port a0 if port c2 is high, and sets port b1 \ in any case. : z portc 2 high? if porta 0 low then portb 0 high ; generates the following code: btfsc 0x07,2 ; skip next instruction if port c2 is low bcf 0x05,0 ; set port a0 low bsf 0x06,1 ; set port b1 high return ; return from word Bank switch optimizations ========================= The compiler tries to remove useless bank manipulations. The following word :: ee@ ( addr -- n ) eeadr ! eepgd bit-set rd bit-set eedata @ ; generates: bsf 0x03,6 ; select bank 2 movwf 0x0d ; write into eeadr (in bank 2) bsf 0x03,5 ; select bank 3 bsf 0x0c,7 ; set bit eepgd of eecon1 (in bank 3) bsf 0x0c,0 ; set bit rd of eecon1 (in bank 3) bcf 0x03,5 ; select bank 2 movf 0x0c,w ; read eedata (in bank 2) bcf 0x03,6 ; select bank 0 decf 0x04,f ; decrement stack pointer movwf 0x00 ; place read value on top of stack return Operation retarget ================== If an operation result is stored on the stack then popped into w, the operation is modified to target w directly. For example, the following word: : timer ( n -- ) invert tmr0 ! ; generates comf 0x00,w incf 0x04,f movwf 0x01 return Bit test operations =================== If a `and' operation before a test can be rewritten using a bit test operation, it will. For example, the code: checksum @ 1 and if parity-error exit then ... will be compiled as: btfsc 0x33,0 goto 0x037 ; parity-error ... Using an explicit bit-test holds the same result: porta 3 high? if exit then will be compiled as: btfsc 0x05,3 return Useless loads removed when testing ================================== Before a test, if the z status bit already holds the right result, no extra test will be generated. 9 and dup if 1+ then will be compiled as: movlw 0x09 andwf 0x00,f btfss 0x03,2 incf 0x00,f Also, the compiler detects operation which do not modify neither w or the top of stack. For example, dup checksum xor! dcc-high ! will be compiled as movf 0x00,w xorwf 0x6c,f incf 0x04,f movwf 0x5b Increment/decrement and skip if zero used when possible ======================================================= The following word: : action-times ( n -- ) begin action 1- dup while repeat drop ; will be compiled as: call 0x022 ; call action decfsz 0x00,f goto 0x027 ; jump to `call action' above incf 0x04,f return Values are not normalized when this is not necessary ==================================================== The word: :: x ( n -- flag ) 3 < if a then ; generates addlw 0xFD btfss 0x03,0 call a return The `<' test did not cause the value to be normalized to 0 or -1, as it is not needed. Examples ******** Some files are included as examples with a Makefile. E.g, to build `booster.hex', run `make booster.fs': * `booster.fs' code for a booster which handles overload and overheat signals This also serves as an example for the priority-based multitasker. * `generator.fs' code for a DCC signal generator based on serial commands (work in progress, not functional yet) * `silver.fs' code that runs on a silver card (a smartcard with a 16f876 and a 24c64 serial eeprom) * `taskexample.fs' example of multitasking code using the basic multitasker * `controller.fs' another multitasking example, used to control multiple peripherals and inputs using a serial link * `i2cloader.fs' a flash and eeprom loader using an I2C bus to reprogram the PIC * `spifcard.fs' production code used in the Ambience European project; includes i2c code, dialog with a bq2010 chip, interface with a smartcard reader using a TDA8004, interrupt code for implementing an in-house watchdog, working around I2C bugs and blinking a led, and analog to digital conversion Table of Contents ***************** Preamble Introduction What is that? Why this project? State of the compiler License Why not use Mary? Credits A very short Forth primer Foreword Words Stack and arguments passing Memory access Constant and variables Tests Loops Our first PicForth program The program itself Line by line explanation Generated assembly code An alternate solution Using inlined code Compiler documentation Organisation Compiling Code Interactive mode Literals Default base Stack size Shifting Looping Memory Variables Tables Main program Macros Included files Assembler Interrupts Argument passing Bit manipulation Decrementing and incrementing a memory register Watchdog timer Reading from or writing to EEPROM Reading from or writing to flash memory Map and disassembler code Multitasking Priority-based multitasker Basic cooperative multitasker Libraries Configuration word Caveats and limitations Optimizations Tail recursion Redundant pop/push are removed Direct-access and literal variants Load, store and operations are mixed Condition inversions Bank switch optimizations Operation retarget Bit test operations Useless loads removed when testing Increment/decrement and skip if zero used when possible Values are not normalized when this is not necessary Examples