eForth1  v2.2
eForth1 - eForth for Arduino UNO

Dr. Chen-Hanson Ting, the creator of eForth and one of the inspiring figures of Forth community, wrote:

In all these years, I have thought that the eForth Model is a good model useful for all different processors and microcontrollers, and for all different applications. It is a very simple model for anybody who like to learn Forth and to use it for their own applications.

In 2011, Dr. Ting created *328eForth* to run Forth on Arduino UNO and wrote in his ceForth_33 document:

I was attracted to Arduino Uno Kit and ported eForth to it as 328eForth...writing to flash memory, I had to take over the bootload section which was monopolized by Arduino IDE...I extended Forth dictionary in the RAM memory. It worked. ...., it was only a teaser to entice new people to try Forth on Arduino Uno.

Before Dr. Ting conceded his fight with cancer in May, 2022, I've spent the last 11 months working with him expanding the concept of **"Forth without Forth"** - a new eForth model - he called. Traditionally, Forth is built with a set of core words in low-level assembly language and establish the rest of words with high-level Forth scripts which get boot-strapped on start-up time. Nowadays, build Forth without using Forth, he reasoned that Forth built entirely in high-level languages, specifically in C, can not only greatly simplify the virtual machine, utilizing operating system, but also encourage portability and optimization. Taking the concept forward, we completed new batch of eForths in Javascript, Java, C++, ported them to Windows, ESP32 in just a few months. Dr. Ting presented a video on November, 2021 to *Sillicon Valley Forth Interest Group*. Later, we fancied creating a hardware version eForth with SystemVerilog and joint venture with Don & Demitri's CORE-I FPGA project of *AI & Robotics Group* til Dr. Ting's eventual departure. The project is still active now.

Personnally, I enjoyed the beauty of working on something small and simple, so decided to pick up Dr. Ting's eForth Model and have fun with it. Since his 328eForth was a teaser only, to move it forward formally, there are a few major things I need to make changes to Dr. Ting's implementation i.g. make C-coder friendly macro assembler, remove dependency on extra bootloader programmer, add EEPROM save/load, and support interrupts, ... So, here we go!

What is eForth1?

  • An eForth for Arduino UNO/Nano implemented in C.
  • Use .ino sketch file that can be openned in Arduino IDE and load/run directly onto Arduino MCU.
  • Has 16-bit cells and stacks.
  • Can read/write Arduino GPIO pins.
  • Supports Arduino Timer and Pin Change Interrupts.
  • Has C API to interface with user defined functions written in .ino.
  • Can save/restore app to/from EEPROM.
  • Can be embeded with other Arduino applications.
  • Can become a turnkey system booting from saved EEPROM or enscripted Forth code.

How to install eForth1?

  • From Arduino IDE's Library Manager

    > Make sure you've hooked up one of Arduino Nano/Uno, or a development board that hosts ATmega328

    > from Arduino IDE > Tools > Manage Libraries, enter FORTH in search box

    > find eForth1 in the short list, select the latest version, and click the Install button

    > from Files > Examples, find eForth1 in Examples from Custom Libraries at very buttom section

    > load one of the eForth1 examples, such as 0_hello

    > open Serial Monitor, set baud rate to 115200, and line ending to Both NL & CR

    > hit compile and upload. You should see the 'ok' prompt

  • Or, from GitHub directly, if you prefer managing source codes manually

    > git clone *https://github.com/chochain/eForth1* onto your local Sketch directory

    > copy examples/0_hello/0_hello.ino from sub-directory, then rename it as eforth1.ino

    > open eforth1.ino with Arduino IDE, and setup your Nano/Uno (or ATmega328) development board

    > in eforth1.ino, change the #include <eforth1.h> to #include "./src/eforth1.h"

    > open Serial Monitor, set baud rate to 115200, and line ending to Both NL & CR

    > compile and upload, you should see the 'ok' prompt

Hopefully, thing goes well and you get something like the snip below if eForth1 is uploaded successfully.

  • >

Now type WORDS in the input bar and hit <return> to list all the words supprted by eForth1. It is ready to serve your future fun projects.

  • >

Different from Dr. Ting's

  • Instead of the original 32-bit, CELL is 16-bit, and prmitives are 8-bit opcodes.
  • To save space, primitives are compiled as bytecode and composite words are flagged address pointers.
  • For speed, use direct threading model instead of original subroutine threaded,
  • For the familiarity to the IDE platform, instead of raw GPIO port read/write, eForth1 calls Arduino library functions i.g. PINMODE = pinMode, IN = digitalRead, OUT = digitalWrite, ...
  • Support multi-tasking through timer interrupts. Timer2 ticks at 1ms as the heart-beat with 8 handler slots provided. Timer1 is left free for Servo or other libraries.
  • Pin Change Interrupts are supported on all pins. Handler slots are provided for each of Port B,C, and D.
  • CLOCK returns a 32-bit number, it takes 2 cells off 16-bit stack. Arithmetics for double are also provided. DNEGATE, D+, or D- plus the conversion words D>S, S>D.
  • DELAY does not pause the MCU nor does it interfer with interrupts. It takes a 16-bit value thus max delay time is 32767ms. For longer delay, define word that loops.

Demos

  • LED blinker (assume you have a blue LED on pin 6, or try *this Wokwi project*) 
        > 1 6 PINMODE⏎                           \ set pin 6 for OUTPUT, i.e. pinMode(6, OUTPUT=1)
    > : blue 6 IN 1 XOR 6 OUT ;⏎             \ create a word to toggle the blue LED
    > : blink FOR blue 500 DELAY NEXT ;⏎     \ create a word to blink (i.e. 500ms delay)
    > 9 blink⏎                               \ run 10 cycles (i.e. 9,8,7,...,2,1,0 to on/off 5 times)
  • Timer Interrupt Service Routine (a red LED on pin 5) 
        > 1 5 PINMODE⏎                           \ set pin 5 for OUTPUT
    > : red 5 IN 1 XOR 5 OUT ;⏎              \ create an interrupt service routine (just a regular word)
    > ' red 200 0 TMISR⏎                     \ make the ISR ticked every 0.2 seconds (= 200ms)
    > 1 TIMER⏎                               \ enable timer, now you should see red LED blinking continuously
    > 19 blink⏎                              \ let's have them both blink (blue LED 10 times)
Blinker Serve Interrupt
  • Drives 8 Servos. Demo at *this Wokwi project*
  • Controls 4-legged Robot (8 servos) with ultrasound and IR remote. Demo code in ~/examples/8_kame
Ultrasound Ranging Walking
  • Communicate through Bluetooth (HC-05). Demo code in ~/examples/9_bluetooth

Benchmark

  • Classic 1 million cycles 
        > : inner 999 FOR 34 DROP NEXT ;⏎          \ inner loop (put 34 on stack then drop it)
    > : outer 999 FOR inner NEXT ;⏎            \ create the outer loop
    > : bench CLOCK DNEGATE outer CLOCK D+ ;⏎  \ CLOCK returns a double value
    > zz⏎                                      \ benchmark the 1000x1000 cycles
    > 25492 0 ok>                              \ 25492ms =~ 25.5us/cycle (with one blinking ISR running in the background)

#

To Learn More About Forth?

If your programming language exposure has been with C, Java, or even Python so far, FORTH is quite different. Quote Nick: "It's no functional or object oriented, it doesn't have type-checking, and it basically has zero syntax". No syntax? So, anyway, before you dive right into the deep-end, here's a good online materials.

To understand the philosophy of FORTH, excellent online e-books are here free for you.

Performance Tuning (~15% faster)

  • Check your Arduino IDE installed directory, say C:\Users\myname\AppData\Local\Arduino... on Windows or /home/myname/Arduino/... on Linux,
  • Find the directory hardware -> arduino -> avr,
  • With an editor, open the 'platform.txt' file,
  • Find all three -Os compiler options (i.g. compiler.c.flags=-c -g -Os ...)

    change them to -O3 for speed, -Os (default) for smallest size, -O2 for somewhere in-between

References to Dr. Ting's Original

For Projects small and large