Sunday, March 06, 2016

SIMPL for Beginners - Part 1

It's almost 3 years since I started on the SIMPL project, it has come a long way since it's early beginnings.

This first post, in a series,  is a "catch-up" for those that have come late to the party.

Introduction to SIMPL

0. SIMPL stands for Serial Interpreted Minimal Programming Language. It is intended as a common, interactive hardware exercising language that will run on almost any low-end, resource limited, microcontroller.

So far it has been implemented on the following microcontroller platforms


RFDuino         nRF51822  Cortex M0
STM32F103  Cortex M3
STM32F373  Cortex M4F
STM32F407  Cortex M4F
STM32F746  CCortex M7


Teensy 3.0, 3.1, 3.2

Future development will include PIC16Fxxxx and PIC32MX devices too - made accessible using Pinguino - an Arduino-like IDE for PICs.

1. SIMPL is based, unashamedly on Ward Cunningham's excellent Txtzyme "Nano-Interpreter".  You can find his work on his Txtzyme Github   This should be the starting point of any SIMPL development. First you port the C code of Txtzyme across to whatever microcontroller you wish to use.  Once you have Txtzyme working on your mcu, you can then start to extend it's functionality to include the whole SIMPL featureset.

2. SIMPL is a text-based interpretive tiny language, which interacts with the onchip hardware allowing simple applications to be developed for a variety of very low cost microcontrollers. It fits into about 2Kbytes of Flash and requires a minimum of 512bytes of RAM - so it will work on the smallest of RAM limited microcontrollers.  It needs a uart connection to a PC terminal program - for text input and output. It is primarily aimed at 14 -28 pin low end microcontrollers - but of course, will run on larger parts.

3. SIMPL originally ran on Arduino. It makes use of the Arduino "Wiring" functions - such as digitalRead, digitalWrite, analogRead, analogWrite, millis, micros, delay, delayMicroseconds and Serial. Provided that your microcontroller can offer similar functions to these, SIMPL will work. SIMPL also runs on the Teensy series of mcu boards.

4. SIMPL can be developed for other microcontrollers - including ARM, MSP430, RFDuino, ESP8266 etc using the "Arduino-like" IDEs  such as STM32Duino or Energia for MSP430 and Pinguino for PIC devices. These alternative IDEs will help you with the various "Wiring" functions.

5. SIMPL has been written in C, to make it portable between various microcontrollers. It uses standard Arduino functions to interact with the hardware - which are perhaps not always the smallest or fastest.  These functions can be rewritten for a particular microcontroller to make them both smaler in codesize, more efficient and faster.

6. SIMPL is not a polished final product, but it offers a framework for experimentation and education.  As new hardware or ideas come along, SIMPL can be extended to incorporate them.  The core ideas of SIMPL are easy to understand, and it gives a good insight into how computer languages are written to interact with the hardware.

7.  SIMPL has been developed with the same methodology as some of the tiny languages from the mid-1970s - when computing resources were very limited.  Tiny BASIC, and FORTH grew out of this period.

8. SIMPL can be easily extended to allow for external SPI or I2C peripherals - such as SRAM, sensors.

9. SIMPL needs almost no tools to develop code.  Just IDE with serial terminal.

10. Enjoy SIMPL, extend and modify it if you wish - most of all, have fun!

The Command Set

SIMPL uses single ASCII characters for its commands and integer numbers for arithmetic - this makes the command interpreter a lot easier to write.

Lower Case characters are used for the core primitive functions which are generally built into Flash, and should be present for every implementation of SIMPL.

Punctuation characters and arithmetical symbols are also used as part of the kernel of  primitives.

The choice of primitives was made to make the language memorable and more human readable.

Upper Case characters are "User Words"  - these you can write yourself, test interactively, modify and store in RAM.  On some microcontrollers - they may be stored in non-volatile ferro-electric memory FRAM (MSP430FR series)  or in non-volatile EEprom.

Originally Txtzyme offered just these commands - see Ward Cunningham's Read Me:

a-f      Select an I/O port
h        help - a summary of commands
i         input
k        a loop counter - which decrements each time around the loop  see {}
m       millisecond delay
o       output
p       print the value of variable x followed by carriage return/line feed
s       sample an ADC channel
u       microsecond delay
x       a 16 bit integer variable
{}     code between these braces is repeated as a loop
_ _    characters between the underscores are printed to the terminal

Once you have got Txtzyme ported across to your microcontroller, and have experimented with it, you are well on your way to working with SIMPL.

In the next part I look at how Txtzyme is extended to include the SIMPL framework.

It is likely that this series will be included on a SIMPL wiki - so that all the information is accessible in one place.

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