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README

README


I have been debating learning to use the Parallax Propeller chip

http://www.parallax.com/tabid/407/Default.aspx

since it came out.  Sparkfun just came out with a board

https://www.sparkfun.com/products/11525

So I went ahead and bought one (two).

Unfortunately you cant use it as-is which drives up the cost of this
experiment.  if you dont already have this stuff you will want these

FTDI Basic Breakout 3.3V
https://www.sparkfun.com/products/9873
Break Away Headers
https://www.sparkfun.com/products/116

And do some soldering.  On the nice side of this, the pinout is the same
as the arduino's so you dont have to buy wires and swizzle them about
just plug the breakout board right on the pins (make sure you have it
oriented right of course).

As you would expect from Parallax, they have a simple programming
language for this platform, no it is not BASIC.

And as you would expect I have a desire to try out the instruction set,
assembly language.  On a linux platform not windows.  The tool that
everyone links to is Brad's Spin Tool

http://www.fnarfbargle.com/bst.html

Of which there are three, a gui thing, a compiler and a loader.  I used
the compiler bstc and loader bstl.  It wasnt obvious at first since many
use the spin language, that the same tool supports PASM which is the
propeller assembly language.

So the architecture here is there are 8 individual 32 bit processors
called cogs.  They are identical to each other.  Each cog has
512 32 bit memory locations, of which 16 are special.  So up to 496
instructions.  The architecture of these cogs is such that there are
no registers in the traditional sense, the instructions are essentially
memory based and any of the 512 locations can be used for operands and
results.  Their documentation says it the other way, basically there are
512 registers.  Six of one, half a dozen of another.  Each cog runs
separately, but everything uses a synchronized clock.

All cogs have access to the hub which has 8192 words of ram and 8192 words
of rom.  Shared resources like I/O are managed through the hub in a
round robin fashion so that no two cogs are trying to touch the same
resource at the same time.

So Parallax has this SPIN language, which if I understand right is
interpreted by programs in the cogs.  If you search around looking to
program this thing you will find what I found that there is an LMM they
call it Large Memory Model for assembly.  But it isnt really PASM, it
is also interpreted, it allows larger programs to live in the shared
ram/rom, larger than the 496 locations you have per cog.  The instructions
are said to be (I didnt look too deeply at them) similar to the real
instruction set so that some/many can be executed directly in the cog.
Then if you search further you may find the prop-gcc port.  That really
gets strange because you see registers like r0 and functions end with
mov pc,lr.  This is also not the real instruciton set but an interpreted
one.

For now I am only interested in the real PASM instruction set that
runs on the cogs.

Most of the examples in this repo:

bstc.linux -b myprog.spin
which creates myprog.binary, then
bstl.linux myprog.binary