Arrays

Create a 2D array from a definition

This is Matthias’ code:

: 2d-array ( #x #y -- )
  2dup * cells s" buffer: (array) (array)" evaluate
  <builds , ( addr ) swap , ( #x ) , ( #y )
  does> ( x y -- addr )
  >r ( x y R: addr-to-structure )
  ( check bounds yourself )
  r@ cell+ @ ( #x ) * + cells
  r> @ ( offset addr ) +
;

Note

“( check bounds yourself )” comment exists as Mecrisp-Stellaris has no ‘throw’ definition. otherwide the commant would probably be “>r ( x y R: addr-to-structure ) throw”

CivilCoder> My takeaway; 1. If you know exactly what data you want stored in an array AND it will never change, then use CREATE 2. If you don’t know excactly what data you want now OR it needs to be changed, use BUFFER: 3. ALLOT is mostly useless since you are reserving FLASH space but can’t write to it. Matthias said it has some uses like reserving a chunk of flash memory to be used as a log area.

Data Types

Creating and fetching data from arrays using different data types. Hopefully it clearly shows the methods and results.

Arrays in Forth are just indexes to a named base memory location in the Flash memory space. Arrays can only be created in Flash meaning the data must be initialized.

See also

BUFFERS are used for UNINITIALISED data (Ram).

Data Types

Name	Bits	Description
Word	32	Native Mecrisp-Stellaris data length
Cell	32	Same as Word above
Half Word	16	Half length
Character	8	One Byte
Bit	1	Smallest

note: In Forth $ = 0x or hexadecimal

Emulate c,

Many MCU’s don’t have a native “c,”. Emulate it as below.

\ Emulate c, which is not available in hardware on some chips.

0 variable c,collection

: c, ( c -- )
  c,collection @ ?dup if $FF and swap 8 lshift or h,
                      0 c,collection !
                      else $100 or c,collection !
                      then ;

: calign ( -- )
  c,collection @ if 0 c, then ;

Create Array of Characters

Four 8 bit or “character” items, $3f, $06, $5b and $66

create array $3f c, $06 c, $5b c, $66 c,

Fetch the array data using different data types

Fetch Cells

32 bits

: =cells       4 * array + dup hex. @  hex.  ;

Fetch Half Words

2 bytes or 16 bits

: =halfwords   2 * array + dup hex. h@ hex.  ;

Fetch Characters

one byte or 8 bits

: =characters     array + dup hex. c@ hex.  ;

Fetch using different data types

Note the address fetch increments.

Cells

Parameter	Word	Address	Data	Comments
0	=cells	200003A4	665B063F	All the 8 bit data is packed into a CELL, very efficient.
1	=cells	200003A8	2000038C	reading data in memory, not associated with the array
2	=cells	200003AC	3D060000	reading data in memory, not associated with the array
3	=cells	200003B0	6C6C6563	reading data in memory, not associated with the array

Halfwords

Parameter	Word	Address	Data	Comments
0	=halfwords	200003A4	0000063F
1	=halfwords	200003A6	0000665B
2	=halfwords	200003A8	0000038C	reading data in memory, not associated with the array
3	=halfwords	200003AA	00002000	reading data in memory, not associated with the array

Characters

Parameter	Word	Address	Data	Comments
0	=characters	200003A4	0000003F
1	=characters	200003A5	00000006
2	=characters	200003A6	0000005B
3	=characters	200003A7	00000066

Create Array of Halfwords

create array $3f4f h, $0607 h, $5b55 h, $6666 h,

Fetch the array data using different data types

Fetch Cells

32 bits

: =cells       4 * array + dup hex. @  hex.  ;

Fetch Half Words

2 bytes or 16 bits

: =halfwords   2 * array + dup hex. h@ hex.  ;

Fetch Characters

one byte or 8 bits

: =characters     array + dup hex. c@ hex.  ;

Fetch using different data types

Note the address fetch increments.

Cells

Parameter	Word	Address	Data	Comments
0	=cells	200003A4	06073F4F
1	=cells	200003A8	66665B55
2	=cells	200003AC	2000038C
3	=cells	200003B0	3D060000

Halfwords

Parameter	Word	Address	Data	Comments
0	=halfwords	200003A4	00003F4F
1	=halfwords	200003A6	00000607
2	=halfwords	200003A8	00005B55
3	=halfwords	200003AA	00006666

Characters

Parameter	Word	Address	Data	Comments
0	=characters	200003A4	0000004F
1	=characters	200003A5	0000003F
2	=characters	200003A6	00000007
3	=characters	200003A7	00000006

Create Array of Cells

create array $3f4f1234 , $06075678 , $5b558765 , $66664321 ,

Fetch the array data using different data types

Fetch Cells

32 bits

: =cells       4 * array + dup hex. @  hex.  ;

Fetch Half Words

2 bytes or 16 bits

: =halfwords   2 * array + dup hex. h@ hex.  ;

Fetch Characters

one byte or 8 bits

: =characters     array + dup hex. c@ hex.  ;

Fetch using different data types

Note the address fetch increments.

Cells

Parameter	Word	Address	Data	Comments
0	=cells	200003A4	3F4F1234
1	=cells	200003A8	06075678
2	=cells	200003AC	5B558765
3	=cells	200003B0	66664321

Halfwords

Parameter	Word	Address	Data	Comments
0	=halfwords	200003A4	00001234
1	=halfwords	200003A6	00003F4F
2	=halfwords	200003A8	00005678
3	=halfwords	200003AA	00000607

Characters

Parameter	Word	Address	Data	Comments
0	=characters	200003A4	00000034
1	=characters	200003A5	00000012
2	=characters	200003A6	0000004F
3	=characters	200003A7	0000003F