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 +===== DUMP memory algorithm: display content of main memory =====
  
 +==== DUMP idea ====
 +
 +A DUMP utility is a software tool that allows to inspect main memory and display it in a user readable form.
 +Typically output is composed of several lines that have the structure:
 +
 +Display bytes starting in memory at a given address in hex (or other radix). Behind them is the ASCII representation of these bytes.
 +
 +The DUMP utility is normally called ''DUMP'' and is invoked with parameters which specify what memory to inspect, often start address and length.
 +
 +
 +==== DUMP Implementation ====
 +
 +One way to implement DUMP is to iterate in a loop line by line through memory. Say you want to display 16 bytes in each line, then this loop will start
 +at the start address and increment the address by 16 in each loop iteration. (If you want a different number of bytes in each line, adjust accordingly).
 +
 +When you display memory in a single line you first output the current address and then have two loops that run one after the other iterating both from 0 to 15.
 +The first loop outputs bytes with two hexadecimal digits (or in decimal, or whatever you intend) and the second loop outputs the individual bytes as ASCII characters.
 +
 +As some characters might control the output in a special way (so called control character such as 07 bell, 0A linefeed, 0C formfeed) it is wise to just output a period 
 +instead of the actual character, in order to get a well formatted display.
 +
 +
 +==== Pseudo code for the DUMP implementation ====
 +
 +<code>
 +Function: dump-line ( address -- )
 +  output address (possibly right aligned)
 +  output ":" and some space
 +  
 +  LOOP i from 0 to 15:
 +     output byte in memory at (address+i) as two hexadecimal digits (or in another radix if desired)
 +     output some space
 +  
 +  LOOP i from 0 to 15:
 +     output byte in memory at (address+i) as an ASCII character, "." if that character is a control character (byte<32)
 +     
 +Function: dump ( address length -- )
 +   WHILE length is positive:
 +        dump-line at address
 +        increase address by 16
 +        decrease length by 16
 +</code>
 +
 +==== Minimal Forth implementation of DUMP: ====
 +
 +
 +You can find a [[https://github.com/Project-Forth-Works/Project-Forth-Works.github.io/blob/main/minimalforth.md|Minimal Forth]] implementation of DUMP in [[en:pfw:dump-minimal_forth.fs|dump-Minimal_Forth.fs]].
 +
 +You can use it as follows:
 +
 +<code forth>
 +  ok
 +Create x 100 allot  ok
 +x 100 dump
 +03D694: 05 61 6C 6C 6F 74 08 00 DF 14 00 00 C1 00 08 00   .allot..?...?...
 +03D6A4: 1F 18 00 00 C1 00 08 00 6F 10 00 00 C1 00 08 00   ....?...o...?...
 +03D6B4: 4F 10 00 00 C2 00 08 00 1F 13 00 00 C2 00 08 00   O...?.......?...
 +03D6C4: 8F 30 00 00 C2 00 08 00 DF 14 00 00 C2 00 08 00   ?0..?...?...?...
 +03D6D4: 1F 18 00 00 C2 00 08 00 6F 10 00 00 C2 00 08 00   ....?...o...?...
 +03D6E4: 4F 10 00 00 C3 00 08 00 8F 30 00 00 C3 00 08 00   O...?...?0..?...
 +03D6F4: 5F 13 00 00                                       _... ok
 +</code>
 +
 +As the original Minimal Forth has no output facility other than ''emit'' and ''.s'' (specifically no number formatting and no ''.'' or ''.r'')
 +this implementation seems to be over complicated.
 +
 +We extended Minimal Forth to [[https://github.com/Project-Forth-Works/Project-Forth-Works.github.io/blob/main/minimalforth.md|GenericForth]] to get a
 +more useful small Forth.
 +
 +A DUMP utility in **GenericForth** can be found in [[en:pfw:dump-genericforth.f|dump-GenericForth.f]]
 +This example is factored using the pseudo code description. The character output has been factored into the useful word PEMIT ( char -- ) too.
 +
 +
 +==== Various DUMP Implementations ====
 +
 +Other DUMP implementations can be found at the end of this description.
 +
 +Your system might lack right justified number output or even BASE for printing numbers in other radix systems. The sample implementation in [[en:pfw:twomoredumps.f|twomoredumps.f]] show how to circumvent this.
 +
 +
 +==== Background information ====
 +
 +More about the DUMP utility can found at the [[https://en.wikipedia.org/wiki/Hex_dump|Wikipedia page for hexdump]]
 +
 +Some Forth DUMP implementations display a fixed amount of bytes and leave the updated address on the stack so that
 +you can invoke DUMP repeatedly to display successive regions of memory.
 +
 +==== Possible pitfalls with DUMP ====
 +
 +Some systems have hardware memory protection that is triggered if you access memory outside the reserved area.
 +The dump utility can do so by trying to show this forbidden memory. Triggered memory protect might stop the current process and
 +terminate your session. If necessary a suitable test for the validity of used addresses might be reasonable on such systems so that
 +dump can issue a normal error message (or display dummy data) in theses cases and leave the system / session otherwise intact.
 +
 +==== Contributions ====
 +
 +<html><h2 style="background-color:yellow">Alternative Implementations</h2></html>
 +
 +====== GForth 0.7.3 ======
 +
 +
 +Please note: The below code uses recognisers for numbers and non Generic Forth words: <=  BLANK (BL FILL)
 +
 +<code>
 +\ Adapted from Z79Forth. Validated against GNU Forth 0.7.3.
 +
 +: .doubles ( -- ) $10 0 DO
 +    [CHAR] 0 EMIT I 1 .R SPACE
 +  LOOP ;
 +: .singles ( -- ) $10 0 DO
 +    I 1 .R
 +  LOOP ;
 +: .header ( -- ) 1 CELLS 2* 1+ SPACES .DOUBLES .SINGLES CR ;
 +
 +: .addr S>D <# 1 CELLS 2* 0 DO # LOOP #> TYPE SPACE ;
 +: .data S>D <# # # #> TYPE SPACE ;
 +: tochar DUP BL $7F WITHIN 0= IF DROP [CHAR] . THEN ;
 +
 +VARIABLE start            \ Base addr. of the interesting area
 +VARIABLE bytecount        \ Number of interesting bytes
 +CREATE asciib 16 ALLOT    \ Buffer for the ASCII character dump
 +
 +: dump.initvars.prtheader ( baseaddr bytecount -- align16 )
 +  bytecount ! DUP start ! $-10 AND
 +  ( baseaddr bytecount ) HEX CR .header ;
 +
 +: asciidump asciib $10 TYPE ;
 +
 +: dump.sanitycheck ( baseaddr bytecount -- baseaddr bytecount )
 +    DEPTH 2 < IF ABORT THEN
 +  DUP 0 <= IF ABORT THEN ;
 +
 +: dump.iskip.bcount ( addr -- skipbytecount )
 +  start @ $-10 AND = IF
 +    start @ $F AND EXIT
 +  THEN 0 ;
 +
 +: dump ( baseaddr bypecount -- ) dump.sanitycheck
 +  BASE @ >R
 +  dump.initvars.prtheader >R
 +  BEGIN                   \ R: saved_BASE currentdumpaddr
 +    I $F AND 0= IF        \ Beginning of a dump line
 +      I .addr             \ Print the base block address
 +      asciib $10 BLANK    \ Initialize the ASCI dump area
 +    THEN
 +
 +    I dump.iskip.bcount ?DUP IF
 +      \ Interesting data not reached yet
 +      DUP 3 * SPACES
 +      R> + >R             \ Skip the uninteresting part
 +    THEN
 +
 +    I C@ DUP .data
 +    tochar I $F AND asciib + C!
 +    bytecount DUP @ 1- OVER !  \ bytecount
 +
 +    @ 0= IF              \ Last dump line
 +      $F I $F AND - 3 * SPACES
 +      asciidump SPACE
 +      R> DROP R> BASE !
 +      EXIT                \ We are done here.
 +    THEN
 +
 +    R> 1+ >R
 +    I $F AND 0= IF        \ Last column of non-last line
 +      asciidump CR
 +    THEN
 +  AGAIN ;
 +
 +</code>
 +
 +[[en:pfw:welcome|Back to PFW page]]
 +
 +~~DISCUSSION~~