What tools and approaches for programming 486 boards?

I have access to some 486 (and 386) single board computers that I'd
like to utilize for some one-off projects.  While I've programmed PCs
under DOS (Windows too, but I have no need for Windows on these
boards), I've never programmed an x86 SBC.  I have, BTW, programmed
plenty of embedded stuff using other processors.  Can any of you folks
who have done so tell me something about my options in the 32-bit x86
embedded world?

I gather that I could stick a DOS on these and program them using a
16-bit compiler.  I do have MSVC++ 1.52c which includes a 16-bit
compiler.  What other options would I have for 16-bit programming?

What about 32-bit code (the idea of having to think about nears and
fars again gives me pause)?  What's involved in writing 32-bit code for
a 486 SBC?

Oh, and I'll probably want to use an RTOS for one or two of these
projects.  Would I be able to e.g. launch an RTOS from DOS?  What about
running an RTOS in 32-bit mode?  I'd incline to something free like
uC/OS-II or FreeRTOS or eCos (none of which I've used before, but I've
used a number of others that the bosses paid for).  Any thoughts there?

To summarize, I want to program some 486 SBCs, and I have some bias
towards 32-bit code but it's not a must, and I want to do it cheaply
and easily, and will probably want an RTOS at some point.  Not too much
to ask, eh? :-)

> I gather that I could stick a DOS on these and program them using a
> 16-bit compiler.  I do have MSVC++ 1.52c which includes a 16-bit
> compiler.  What other options would I have for 16-bit programming?


Take a look at http://www.openwatcom.org and http://www.freedos.org if you
would like a 16bit environment, with perhaps a DOS extender.

Alternatively try http://www.delorie.com/djgpp/ for a 32bit under DOS.

Both these tools are open source.

>
> What about 32-bit code (the idea of having to think about nears and
> fars again gives me pause)?  What's involved in writing 32-bit code for
> a 486 SBC?


Using DOS extenders can be a headache, having both real and protected mode
ISR's.  If you want 32bit protected mode and have a few $ to spare, then
http://www.on-time.com provide a very nice system.  You say you want to do
it cheaply, but this is a relative term.  The on-time tools are relatively
cheap compared to others, but still you must part with some cash.



> Oh, and I'll probably want to use an RTOS for one or two of these
> projects.  Would I be able to e.g. launch an RTOS from DOS?

The on-time product allows you to do exactly this.  Very nice.

>What about
> running an RTOS in 32-bit mode?  I'd incline to something free like
> uC/OS-II or FreeRTOS or eCos (none of which I've used before, but I've
> used a number of others that the bosses paid for).  Any thoughts there?


FreeRTOS.org is 16bit only (unless you want to provide a port :-)   ), x86
is not a primary target other than the low end 1/286.   Not sure about
uC/OS-II, but this is only free if you are not intending on creating a
commercial product.

Regards,
Richard.

http://www.FreeRTOS.org

Mike Silva wrote:
> 
... snip ...
> 
> To summarize, I want to program some 486 SBCs, and I have some
> bias towards 32-bit code but it's not a must, and I want to do it
> cheaply and easily, and will probably want an RTOS at some point. 
> Not too much to ask, eh? :-)

Check out DJGPP, at www.delorie.com.  No need to restrict yourself
to 16 bit code.

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> I have access to some 486 (and 386) single board computers that I'd
> like to utilize for some one-off projects.  While I've programmed PCs
> under DOS (Windows too, but I have no need for Windows on these
> boards), I've never programmed an x86 SBC.  I have, BTW, programmed

One tends to design in x86 only when running a COTS OS is part of the
design requirements. Otherwise it's not a very efficient solution.

I'd recommend looking at various realtime Linux flavors on the 486s.