nanoFORTH Operations

Internal

At its core, nanoFORTH is a traditional parse-dispatch virtual machine interpreter with twin stacks. Essentially, it is a parser and a big switch loop. Like every other FORTH, it has a dual-personality which toggles between interpreter mode and compiler mode. In interpreter mode, it runs interactively not unlike an old HP hand-held calculator. When in compiler mode, it transcodes user defined functions into token threaded code which is compact and portable. The latter ability enables future units to exchange not only data packets but also instruction code segments to each other. This can bring a big grin but, of course, we later might need to deal with the red flag raised by security concerning parties.

Compared to any FORTH language tutorial, you probably will notice that the length of a word of nanoFORTH, unlike most are 31-character, is 3 characters or less. Core vocabulary is a short list which means makers need to define one if a more elaborated function is needed. There is no floating-point or meta-compiler supported. These depart from standard FORTHs and begs the question of whether nanoFORTH is truly a FORTH. Well, our target platform is a very small MCU and our application has probably a dozen of functions. Aside from saving a few bytes, it has the benefit in simplifying internal searching. The theory says that our brain is pretty good at filling the gap. So, hopefully, with a little bit creativity, our code can be clean and still maintainable. To qualify it as a FORTH or not, probably doesn't matter that much so long as it behaves well, runs fast enough, and useful for our needs.

Arduino Nano Memory Map

address object growth Forth EEPROM

0x900 Arduino RAM max _ . .

0x8f6 global/static variables/Arduino heap ⇩ . .

... ... ... . .

0x618 Forth input buffer ⇧ X .

0x617 return stack ⇩ X .

... 0x100 shared space ... X .

0x518 data stack ⇧ X .

... user defined words ⇧ X X

0x1e8 user dictionary starts ⇧ X X

... Arduino libraries _ . .

0x100 Arduino RAM starts _ . .

0x000 Arduino registers _ . .

Note, we have the 1K EEPROM sitting on the side which can save and restore the user dictionary when instructed.

Number Representation

nanoFORTH handles only integer numbers.

16-bit integer range -32727 to 32726
32-bit double can be presented as two 16-bit numbers on data stack
hex number can be input with $ prefix

Examples

20 ⏎ ➤ 20_ok
10 $10 ⏎ ➤ 20_10_16_ok

Built-in Words

Stack Ops

opcode stack description

DRP ( w -- ) drop

DUP ( w -- w w ) duplicate

SWP ( a b -- b a ) swap

OVR ( a b -- a b a ) over

ROT ( a b c -- b c a ) rotate

Examples

20 10 ⏎ ➤ 20_10_ok
OVR ⏎ ➤ 20_10_20_ok
DRP ⏎ ➤ 20_10_ok
SWP ⏎ ➤ 10_20_ok
DUP ⏎ ➤ 10_20_20_ok
ROT ⏎ ➤ 20_20_10_ok

Arithmatics Ops

opcode stack description

+ ( a b -- a+b ) add

- ( a b -- a-b ) subtract

* ( a b -- a*b ) multiply

/ ( a b -- a/b ) divide

MOD ( a b -- a%b ) modulo

NEG ( a -- -a ) negate

ABS ( a -- abs(a) ) absolute value of a

MIN ( a b -- min(a, b) ) minimum value between a and b

MAX ( a b -- max(a, b) ) maximum value between a and b

Examples

17 5 + ⏎ ➤ 22_ok
1 2 3 4 + + + ⏎ ➤ 10_ok
10 3 / ⏎ ➤ 3_ok

Binary and Logical Ops

opcode stack description

AND ( a b -- a&b ) binary and

OR ( a b -- aIb ) binary or

XOR ( a b -- a^b ) binary xor

NOT ( a -- ^a ) binary not

LSH ( n i -- n<<=i ) left shift

RSH ( n i -- n>>=i ) right shift

= ( a b -- a==b ) equal

< ( a b -- a<b ) less than

> ( a b -- a>b ) greater than

<> ( a b -- a!=b ) not equal

Word Definition and Dictionary Ops

opcode stack immediate description

: ( -- ) yes start defining a new word

; ( -- ) yes end of word definition

WRD ( -- ) yes list all words defined in nanoFORTH dictionaries

FGT ( -- ) yes forget/remove functions

HRE ( -- w ) get current user dictionary pointer

Flow Control (in Compiler mode only)

branching ops description

f IF xxx THN conditional branch

f IF xxx ELS yyy THN

BGN xxx f UTL

BGN xxx f WHL yyy RPT

n FOR xxx NXT for loop, index value I count down from n to 1

Return Stack Ops (in Compiler mode only)

opcode stack immediate description

I ( -- w ) fetch word from top of return stack, aka R@ in other FORTHs

>R ( w -- ) push word on top of data stack onto return stack

R> ( -- w ) pop top of return stack value and push it onto data stack

note: FORTH programmers often use return stack as temp storage. However do use >R and R> carefully and in Compile mode only or you risk messing up call depth which can crash FORTH interpreter.

Memory Access Ops

opcode stack immediate description

@ ( a -- w ) fetch a 16-bit value from memory address 'a'

! ( a w -- ) store a 16-bit value to memory address 'a'

C@ ( a -- w ) fetch a single byte from memory address 'a'

C! ( a w -- ) store a byte (or lower byte of the word) to memory address 'a'

note: the above opcodes read/write nanoFORTH memory space directly. It provides the power to peek and poke random memory but also to shoot yourself on the foot. Use with caution.

Examples see next section

Variable, Constant, and Array Ops

opcode stack immediate description

VAR ( -- ) yes define a 16-bit variable

VAL ( w -- ) yes define a 16-bit value (i.e. constant)

ALO ( w -- ) allocate extra w bytes on user dictionary (for array allocation)

Examples

VAR x ➤ ok (a variable x is created on user dictionary)
3 x ! ➤ ok (store 3 into variable x)
x @ 5 + ➤ 8_ok (fetch value of x add 5 to it)

32 VAL N ⏎ ➤ ok (a const N is created on user dictionary)
N 1 + ⏎ ➤ 33_ok

VAR z 6 ALO ⏎ ➤ ok (a variable z with 8 (2+6 extra) bytes allocated, i.e. z[0..3])
5 z 4 + ! ⏎ ➤ ok (5 is stored into z[2])
z 4 + @ ⏎ ➤ 5_ok (retrieve z[2] onto data stack)

Console I/O

opcode stack immediate description

KEY ( -- c ) get a byte from input console

EMT ( c -- ) write a byte to output console

CR ( -- ) send a <return> to console

. ( w -- ) print the value on data stack to output console

." `( -- )` send the following string (terminated with a ") to output console

S" `( -- a n )` put string (terminated with a ") address and length on TOS

TYP ( a n -- ) type the string at address with length n

HEX ( -- ) yes change input/output to hexadecimal i.e. base 16

DEC ( -- ) yes change input/output to decimal i.e. base 10

Examples

: hi FOR ." hello!" 33 EMT CR NXT ; ⏎ ➤ ok (hi is now defined in user dictionary)
3 hi ⏎
➤ hello!
➤ hello!
➤ hello!ok : s1 S" one!" ; : s0 S" zero!" ;⏎ ➤ ok (s1 s0 are defined in user dictionary)
: chk IF s1 ELS s0 THN TYP ;⏎ ➤ ok
1 chk ⏎
➤ one! ok
0 chk ⏎
➤ zero! ok

Reset, Debug, and Tracing

opcode stack immediate description

BYE ( -- ) yes reset nanoFORTH on Arduino, exit to OS on other platform

DMP ( a w -- ) yes dump nanoFORTH user dictionary from address 'a' for w bytes

TRC ( t -- ) enable/disable execution tracing

Examples

EEPROM Access

opcode stack immediate description

SAV ( -- ) yes save user dictionary into Arduino Flash Memory

LD ( -- ) yes restore user dictionary from Arduino Flash Memory

SEX ( -- ) yes SAV with autorun flag set in EEPROM for reboot/execution

Arduino Specific Ops

|opcode|stack|immediate|description| |:–|:–|:–| |CLK|( -- d )|fetch Arduino millis() value onto data stack as a double number| |DLY|( w -- )|wait milliseconds (yield to hardware tasks)| |PIN|( w p -- )|pinMode(p, w)| |IN |( p -- w )|digitalRead(p)| |OUT|( w p -- )|if p=0x0xx, digitalWrite(xx, w),
if p=0x1xx, xx masks PORTD (pin 0~7) i.e. multi-port write,
if p=0x2xx, xx masks PORTB (pin 8~13)
if p=0x3xx, xx masks PORTC (analog A0~A6)| |AIN|( p -- w )|analogRead(p)| |PWM|( w p -- )|analogWrite(p, w)|

Examples

1 13 OUT ⏎ ➤ ok (built-in LED is turn on, i.e. digitalWrite(13, 1) called)
$F0 $1F0 OUT ⏎ ➤ ok (turn on pin 4,5,6,7 at once)

C API function call

|opcode|stack|description| |:–|:–|:–|:–| |API|( n -- )|call API by number registered via ef_api(n, func) in Arduino sketch|

Interrupt ops

opcode stack immediate description

TMI ( n i -- ) yes set timer ISR with period at n microsecond. n is a U16 unsigned number i.e. max ~64 seconds

PCI ( p -- ) yes capture pin #p change (either HIGH to LOW or LOW to HIGH)

TME ( f -- ) enable/disable timer interrupt, 0:disable, 1:enable

PCE ( f -- ) enable/disable pin change interrupt, 0:disable, 1:enable

Note: nanoForth utilizes timer2 for timer interrupt. It might conflict with libraries which also uses timer2 such as Tone().

Examples

: s_a 65 emt ; ➤ ok (define a word s_a which emit 'A' on console)
: s_b 66 emt ; ➤ ok (define a word s_b which emit 'B' on console)
10000 0 TMI s_a ➤ ok (set s_a in handler slot #0, tigger every 10 seconds)
25000 1 TMI s_b ➤ ok (set s_b in handler slot #1, tigger every 25 seconds)
1 TME ➤ ok (enable timer interrupt)
AABAAABAABAA (interrupt routines been called)
0 TME ➤ ok (disable timer interrupt)

8 PCI s_a ➤ ok (run s_a when pin 8 changed)
1 PCE ➤ ok (enable pin change interrupt)
AA (assuming you have a push button hooked up at pin 8)

Double precision (i.e. 32-bit) Arithmatic (for Arduino Clock mostly)

opcode stack description

D+ ( d1 d0 -- d1+d0 ) add two doubles

D- ( d1 d0 -- d1-d0 ) subtract two doubles

DNG ( d0 -- -d0 ) negate a double number

Examples

CLK 1000 DLY CLK D- DNG ⏎ ➤ 1000_0_ok

Meta Programming (available only via source recompilation with N4_DOES_META set to 1 in n4_asm.h)

opcode stack description

CRE ( -- ) create a word with link and name field

, ( n -- ) comma, add a 16-bit value onto dictionary

C, ( n -- ) byte comma, add a 8-bit value onto dictionary

' ( -- xt ) tick, fetch xt (parameter field address) of a word

EXE ( xt -- ) execute an xt address

Examples

: aa 123 ; ⏎ ➤ ok (create a word) CRE bb ⏎ ➤ ok (create a empty word bb with it link and name field only) ' aa ⏎ ➤ 5_ok (aa's xt address is put on top of stack) $C0 OR , ⏎ ➤ ok (combile the address and call flag onto dictionary) $F0 , ⏎ ➤ ok (compile RET opcode onto dictionary) bb ⏎ ➤ 123_ok (bb calls aa, so returns 123 on stack) ' bb ⏎ ➤ 123_11_ok (get bb's xt address) EXE ➤ 123_123_ok (execute bb's xt directly)

Function/Word Struct

size field

fixed 16-bit address to previous word, 0xffff is terminator

fixed 3-byte function name

n-byte
depends on the length of the function * compiled opcodes (see next section), or
* address of a user defined word

Opcode Memory Formats

opcode stack description

1-byte literal 0nnn nnnn 0..127, often used, speeds up core

3-byte literal 1011 1111 snnn nnnn nnnn nnnn 16-bit signed integer

1-byte primitive 10oo oooo 6-bit opcode i.e. 64 primitives

branching opcodes 11BB aaaa aaaa aaaa 12-bit address i.e. 4K space

n-byte string len, byte, byte, ... 256 bytes max, used in print string

1. Why - Review nanoFORTH command examples
2. How - Intall nanoFORTH

address	object	growth	Forth	EEPROM
0x900	Arduino RAM max	_	.	.
0x8f6	global/static variables/Arduino heap	⇩	.	.
...	...	...	.	.
0x618	Forth input buffer	⇧	X	.
0x617	return stack	⇩	X	.
...	0x100 shared space	...	X	.
0x518	data stack	⇧	X	.
...	user defined words	⇧	X	X
0x1e8	user dictionary starts	⇧	X	X
...	Arduino libraries	_	.	.
0x100	Arduino RAM starts	_	.	.
0x000	Arduino registers	_	.	.

opcode	stack	description
DRP	`( w -- )`	drop
DUP	`( w -- w w )`	duplicate
SWP	`( a b -- b a )`	swap
OVR	`( a b -- a b a )`	over
ROT	`( a b c -- b c a )`	rotate

opcode	stack	description
+	`( a b -- a+b )`	add
-	`( a b -- a-b )`	subtract
*	`( a b -- a*b )`	multiply
/	`( a b -- a/b )`	divide
MOD	`( a b -- a%b` )	modulo
NEG	`( a -- -a )`	negate
ABS	`( a -- abs(a) )`	absolute value of a
MIN	`( a b -- min(a, b) )`	minimum value between a and b
MAX	`( a b -- max(a, b) )`	maximum value between a and b

opcode	stack	description
AND	`( a b -- a&b )`	binary and
OR	`( a b -- aIb )`	binary or
XOR	`( a b -- a^b )`	binary xor
NOT	`( a -- ^a )`	binary not
LSH	`( n i -- n<<=i )`	left shift
RSH	`( n i -- n>>=i )`	right shift
=	`( a b -- a==b )`	equal
<	`( a b -- a<b )`	less than
>	`( a b -- a>b )`	greater than
<>	`( a b -- a!=b )`	not equal

opcode	stack	immediate	description
:	`( -- )`	yes	start defining a new word
;	`( -- )`	yes	end of word definition
WRD	`( -- )`	yes	list all words defined in nanoFORTH dictionaries
FGT	`( -- )`	yes	forget/remove functions
HRE	`( -- w )`		get current user dictionary pointer

branching ops	description
f IF xxx THN	conditional branch
f IF xxx ELS yyy THN
BGN xxx f UTL
BGN xxx f WHL yyy RPT
n FOR xxx NXT	for loop, index value I count down from n to 1

opcode	stack	description
I	`( -- w )`	fetch word from top of return stack, aka R@ in other FORTHs
>R	`( w -- )`	push word on top of data stack onto return stack
R>	`( -- w )`	pop top of return stack value and push it onto data stack

opcode	stack	description
@	`( a -- w )`	fetch a 16-bit value from memory address 'a'
!	`( a w -- )`	store a 16-bit value to memory address 'a'
C@	`( a -- w )`	fetch a single byte from memory address 'a'
C!	`( a w -- )`	store a byte (or lower byte of the word) to memory address 'a'

opcode	stack	immediate	description
VAR	`( -- )`	yes	define a 16-bit variable
VAL	`( w -- )`	yes	define a 16-bit value (i.e. constant)
ALO	`( w -- )`		allocate extra w bytes on user dictionary (for array allocation)

opcode	stack	immediate	description
KEY	`( -- c )`		get a byte from input console
EMT	`( c -- )`		write a byte to output console
CR	`( -- )`		send a <return> to console
.	`( w -- )`		print the value on data stack to output console
."	`( -- )`		send the following string (terminated with a ") to output console
S"	`( -- a n )`		put string (terminated with a ") address and length on TOS
TYP	`( a n -- )`		type the string at address with length n
HEX	`( -- )`	yes	change input/output to hexadecimal i.e. base 16
DEC	`( -- )`	yes	change input/output to decimal i.e. base 10

opcode	stack	immediate	description
BYE	`( -- )`	yes	reset nanoFORTH on Arduino, exit to OS on other platform
DMP	`( a w -- )`	yes	dump nanoFORTH user dictionary from address 'a' for w bytes
TRC	`( t -- )`		enable/disable execution tracing

opcode	stack	immediate	description
SAV	`( -- )`	yes	save user dictionary into Arduino Flash Memory
LD	`( -- )`	yes	restore user dictionary from Arduino Flash Memory
SEX	`( -- )`	yes	SAV with autorun flag set in EEPROM for reboot/execution

opcode	stack	immediate	description
TMI	`( n i -- )`	yes	set timer ISR with period at n microsecond. n is a U16 unsigned number i.e. max ~64 seconds
PCI	`( p -- )`	yes	capture pin #p change (either HIGH to LOW or LOW to HIGH)
TME	`( f -- )`		enable/disable timer interrupt, 0:disable, 1:enable
PCE	`( f -- )`		enable/disable pin change interrupt, 0:disable, 1:enable

opcode	stack	description
D+	`( d1 d0 -- d1+d0 )`	add two doubles
D-	`( d1 d0 -- d1-d0 )`	subtract two doubles
DNG	`( d0 -- -d0 )`	negate a double number

opcode	stack	description
CRE	`( -- )`	create a word with link and name field
,	`( n -- )`	comma, add a 16-bit value onto dictionary
C,	`( n -- )`	byte comma, add a 8-bit value onto dictionary
'	`( -- xt )`	tick, fetch xt (parameter field address) of a word
EXE	`( xt -- )`	execute an xt address

size	field
fixed 16-bit	address to previous word, 0xffff is terminator
fixed 3-byte	function name
n-byte depends on the length of the function	* compiled opcodes (see next section), or * address of a user defined word

opcode	stack	description
1-byte literal	`0nnn nnnn`	0..127, often used, speeds up core
3-byte literal	`1011 1111 snnn nnnn nnnn nnnn`	16-bit signed integer
1-byte primitive	`10oo oooo`	6-bit opcode i.e. 64 primitives
branching opcodes	`11BB aaaa aaaa aaaa`	12-bit address i.e. 4K space
n-byte string	`len, byte, byte, ...`	256 bytes max, used in print string