some newbie questions

Joel Sherrill joel.sherrill at
Fri Feb 13 16:14:50 UTC 2004

gregory.menke at wrote:
> sebastian ssmoller writes:
>  > hi,
>  > i am new to rtems. i looked around in the docs and sources and i find it
>  > really interesting. 
>  > 
>  > i am currently working in two projects using some developer board (ip
>  > 460) with a 68040 (host) and a 68360 (communication) cpu on it. further
>  > more these boards have CAN (controller area network) controller support.
>  > 
>  > the more i look inside the rtems stuff the more i wonder whether it
>  > could be possible to adopt rtems for my needs.
> Learning the RTEMS source is a fairly long process, you have to learn
> a lot about it before you start to understand.  If you can't find
> something, please ask on this list.

There is a lot of source but it follows a very regular pattern.
There are places in the source where you see a set of CPUs and
under those directories you may see further divisions by
CPU model and/or Board.

Sebastian... The gen68360_040 BSP is what you want.  It's there
and should be a good starting point for you.  It should support
everything you have but the CANBus controller.  See
c/src/lib/libbsp/m68k/gen68360 for the BSP source.

An RTEMS "generic" BSP like the gen68360 may have to be tinkered
with to match a particular use of the "system on chip" type
CPU.  There are always variations in how the CPU is actually
used on a board.  On some generic BSPs, there are only a few
options and a central place to control them.  On others, there
are lots of variations in plugging the CPU into a board and you
might have to hunt a bit more.

>  > so could you please help me to answer some remaining questions (or
>  > just point me to the right place in your documentation set):
>  > 
>  > - how do i install rtems on the target plattform ? i currently use
>  >   serial line. 
> That entirely depends on the capablities of the target platform.  If
> your target has a boot monitor that can use a serial port to download
> an image in some way, that will work.  If it can manage a network
> interface, it might be able to tftp the image- which is lots more
> convienent (and faster).

I don't know what your board has on it in the way of a ROM monitor
but that is the usual way to download to a board of this type.
Some boards have a ROM monitor that will use tftp to download an
application from a server.  This is useful for testing.  Check
out MyRightBoot or MicroMonitor if you don't have a ROM monitor.

>  > - is it possible to write and use my own scheduler ?
> I suppose- but why?  RTEMS's is very configurable and very bug-free.
> If you want to add a new scheduling algorithm or modify one, make a
> more detailed proposal and we all can comment on where/how and how
> difficult it might be.

And port your own network stack and many many other features that
come for free with RTEMS.

>  > - how difficult would it be to add CAN Controller support to rtems ?
> A user-space driver would be easiest- meaning you integrate the driver
> with your project code and call it directly.  Further integration into
> RTEMS depends largely on what you want it to do.

The powerpc/eth_comm already has a CanBus driver.

>  > - what requirements does rtems have ? (disk ?, memory ?)
>  > 
> The OS image footprint ranges from ~100k up to several hundred,
> depending on what you compile in.  Your code adds to that of course.
> There is no disk footprint as such on the target.  The cross-compiler
> suite and development libraries can consume a good bit on the
> development host.

I recall that on the 68360 you can run an ftp and http webserver
in about 256K code space.

> Gregm

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