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SwapForth on j1a

This is a 16-bit version of SwapForth, intended as an interactive Forth system using very little logic and RAM. See below for exactly how little.

Running the binary

After installing the icestorm tools, you can run on a Lattice iCEstick like this

iceprog icestorm/j1a.bin
PYTHONPATH=../shell:$PYTHONPATH python shell.py -h /dev/ttyUSB0 -p ../common/

(where /dev/ttyUSB0 is the appropriate port your iCEstick was assigned).

You should get something like

Contacting... established
Loaded 196 words

And you can now try the usual Forth things, e.g.

1 2 + .

There is a fairly complete core ANS-compatible Forth system running on the board, including a compiler.

Some demos

You can control the five on-board LEDs

$00 leds
$1f leds

and to make them blink

: blink
  32 0 do
    i leds
    100 ms

There is an Easter date calculator.

#include ../demos/easter.fs

Now you can do

>2015 .easter
2015 April 5   ok

Or even

>: 20easters
+  2035 2015 do
+    cr i .easter
+  loop

2015 April 5 
2016 March 27 
2017 April 16 
2018 April 1 
2019 April 21 
2020 April 12 
2021 April 4 
2022 April 17 
2023 April 9 
2024 March 31 
2025 April 20 
2026 April 5 
2027 March 28 
2028 April 16 
2029 April 1 
2030 April 21 
2031 April 13 
2032 March 28 
2033 April 17 
2034 April 9   ok

Building from Scratch

After installing the icestorm tools, run

make -C icestorm

this will produce j1a.bin - but it only contains the very bare-bones system; the rest of SwapForth still needs to be compiled. Load j1a.bin as above, and on connecting on the board you should see

Contacting... established
Loaded 127 words

Compile the rest of SwapForth and write the finished executable by

#include swapforth.fs
#flash build/nuc.hex

Now run make j1a again - this compiles an FPGA image with the complete code base built-in.

Deploying an Embedded Application

To make a flash image that turns the LEDs on at boot:

:noname -1 leds quit ; init !
#flash build/nuc.hex

To make an image that continously blinks the LEDs:

: blink 0 begin dup leds 1+ 10 ms again ;
' blink init !
#flash build/nuc.hex

To make an image that blinks on power up, but on reset will run the command prompt:

:noname ['] quit init ! blink ; init !
#flash build/nuc.hex


The FPGA on the iCEstick has 8Kbytes of RAM. SwapForth's base system takes up about 5Kbytes of this, leaving about 3K for your use.

The j1a and its current peripherals (LEDs, uart) take 1162 of the available 1280 logic cells on the iCE40 HX1K. So there is room for some more peripherals.