Problems with the blackfin port

[Allan Hessenflow]

Alain Schaefer wrote:
> Which puts architecure dependent code in parts of the rtems codebase which
> are clearly
> architecture independent. I am almost 100% this patch will not get accepted.
> Even if it
> is "protected" by a #IFDEF.

The version I've done does not require any modification of the rtems codebase
besides the bfin specific files in cpukit/score/cpu/bfin/.  Basically, the
ISR, just prior to doing a RTI, does a RAISE 15.  So as soon as the RTI has
executed, the level 15 interrupt handler is entered.  That handler calls
thread dispatch, and can do an RTI to return.  This does require that 
self-nesting be enabled.

The only thing making me a little uncomfortable with this approach is that
the interrupt controller is not documented sufficiently to determine if
this might introduce some additional limit to the number of tasks that can
exist (the maximum nest level is the number of tasks).  The hardware has to
in some way keep track of the nesting level because the outermost RTI would
switch from supervisor mode back to user mode (we don't ever let it get that
far; everything is run from inside one level 15 interrupt).

Anyway, it does seem to work; it's only the fact that I haven't had time to
do much testing that has stopped me from submitting the changes yet.  Let
me know if either of you would like to try it.

allan

-- 
Allan N. Hessenflow      allanh at kallisti.com