Well, I could easily assume that from where you sent this email it was
April 1st when you sent it, but then I'd have to assume that the entire
world enjoys the American April 1st holiday, which would then expose me
as the sort of ameri-centric snob I've worked so long to hide.

So I'll assume this is a serious request for help and feed the trolls,
er, I mean expose some of the issues you'll run into when you design
Linux into a PIC.

First of all, don't let anyone tell you it can't be done.  Anything is
possible, though there are some tradeoffs:

First, the PIC has no MMU.  Heck, it doesn't really even have a fully
manipulable stack.  Linux typically requires at minimum an MMU, but some
smart folks somewhere on the internet have cobbled together an embedded
MMU-less version of linux.  Find it and learn from them.  Also find out
what kind of life they lead, and expect to live that life for the
remainder of your development period.

Second, the PIC doesn't really have a fully capable ANSI C compiler.
Don't worry, linux won't compile on just any old ANSI compiler anyway.
Go ahead and pull out your copy of C18 and run it on a few linux source
files.  When it runs into a problem, comment that line out.  You can
always sort it out later.  Don't let anyone fool you about linking -
just copy all the object files into one big file (cp *.o linux.obj, for
instance) and let the PIC worry about it.  Then find a PIC with a large
enough code space to hold the entire thing.  Be aware, though, that
since you commented out most of the code in an earlier step, you may
need a larger PIC when you get all that sorted out.

Thirdly, After realizing the futility of compiling linux directly for
the PIC, take up the bright idea of creating an emulator that runs on
the PIC.  You can pick an existing core which already has emulators in C
(such as ARM, MIPS, x86, HAL9000, etc) or make up your own.  Tha
advantage of picking one that exists is you don't have to create the C
compiler as well.  Code up the emulator for the PIC, and create external
address/data busses for flash and ram.  Look up the PCI spec and try to
emulate that bus standard - it'll save you loads of time adding
peripherals later.  The performance of the system may be low (a few
hundred instructions per second of emulated code) but be content in the
fact that you were able to shoehorn Linux into an 8-bit microcontroller.

All it'll take, really, is a bunch of elbow grease and headlamp fluid.
Good luck!  Keep us informed of your progress, ok?

-Adam

P.S.  While the post is mainly in jest, the third option really would
work.  The PIC, after all, is Turing Complete, and in theory can perform
any logical sequence of steps.  I just can't see the educational value
in doing it...

Vishal Changrani wrote:

>hi,
>hi to all you big guys there..man ..after reading your questions and answers i feel i m still in nursery :(
>anyway heres my question:
>I want to develop (or rather 'Port') the linux kernel on to the Pic16f877. Now the reason I wish to do this is:
>1. I have to present a research paper due on april 22nd on the topic Real Time operating Systems: Case Study Microcontrollers.
>2. I think since both Linux and PIc are so very commercially successful in there respective domains that it would be good idea to combine them in some way.
>3. I love linux and the PIC and couldnt think of a better topic.
>About the Real time part I think i will save that till later that is after I have finsihing porting Linux to the PIC (if I am able to do it i.e.)
>
>Now i went through a book - Building Embedded Linux Systems ..and it says that it isnt easy (not impossible ) though to port linux on to a 'less than 32 bit' microcontroller or microprocessor. So I am stuck now! since Microchip doesnt offers a 32 bit microcontroller.
>Please suggest me something! anything!
>
>Thankyou
>Bye
>Vishal
>
>
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