rbpic v1.0.0 released

Get it here!

Why?

In 2006 I decided to learn how to make my own LED hardware. My first project that involved RGB LEDs used a PIC10F202 and three transistors to pulse-width modulate each color. While the design of this project was really simple, I had to learn schematic/capture, layout, manufacturing and how to write PIC assembly. (Unfortunately, the Arduino was not widely known when I embarked on my adventure so if you wanted your LEDs to go bleep-bloop you needed your own hardware platform or a big, bulky devkit.)

I knew exactly what I wanted each LED node to do: cycle the R, G and B diodes through an ascending/descending sequence of brightness values. The theory being that as each color diode was manipulated independently the LED would slowly work through each possible color combination. When I sat down to write the initial test code using assembly I found the language to be quite tedious. After writing enough code to verify that the circuit worked I decided to make my life easier by writing a higher-level assembly syntax using Ruby.

Though the final high-level assembly I wrote -- which I had taken to calling RSM -- was not insanely maintainable, I still find it easier to understand than plain assembly. And the resulting LED behavior was pretty neat:

What?

I have cleaned up the code and packaged it into a Ruby gem, rbpic, suitable for use (provided you happen to have a PIC10 project in your wheelhouse.) The gem comes with an executable, rbpic-compile, that translates .rsm code into .asm.

Example

Below is a simple program that does nothing to give you a taste of the syntax:

loop(:main) { }

and here is the generated PIC assembly:

    #include "p10f202.inc"
    __config _WDT_OFF & _CP_OFF & _MCLRE_OFF

    org     0x00
    goto    $+2

Four_microsecond_delay
    retlw   0x0
Main
    goto    Main
    end

Here is a more serious example:

constants do
    foo
    bar
end

init_clock

set :foo, 2
set :bar, 1

loop(:main) do
    copy :bar, :foo    
end         

And the resulting assembly:

    #include "p10f202.inc"
    __config _WDT_OFF & _CP_OFF & _MCLRE_OFF

    org     0x00
    goto    $+2

Four_microsecond_delay
    retlw   0x0

    cblock 0x08
            foo
            bar
    endc

    movwf   OSCCAL
    movlw   b'10011000'
    option

    movlw   0x2
    movwf   foo
    movlw   0x1
    movwf   bar

Main
    movf    bar, w
    movwf   foo
    goto    Main
    end

You can read all about the syntax here.

Musings

The code has some warts and annoying, to me, inconsistencies, but I still think it is a good example of what is possible without having to write a full-blown parser/compiler/etc. (There are C and Basic compilers that target PIC processors and they mostly work well provided you can stay within the limits of the free license.)

I also have a new project in mind that will require a PIC18 and I want to update rbpic to support the more complex architecture of that processor. Join me on github if you want to help.