Which PowerPC BSP/libcpu to base new port on?

ahuitzot at mindspring.com ahuitzot at mindspring.com
Thu Nov 21 17:00:18 UTC 2002

I am thinking of porting RTEMS to an mpc555 based board (you may have seen
some of my other posts...) and I was wondering which existing BSP/libcpu code
would be the easiest/best to start with.  So far I have been looking at the
mpc8xx and the mpc8260 libcpu stuff, and I can't find much of a difference
between them.  The biggest differences that stick out to me so far are these:

Clock code:  the mpc8xx stuff uses the PIT to do the clock, while the mpc8260
uses the decrementer.  Which way is better?  Would it be the decrementer

Console code: obviously different between CPU's but thats irrelevent for me,
as I will be completely replacing the console code for the mpc5xx...

Register definitions: I will be replacing these for the mpc5xx, so any
differences here will not sway my decision either...

Exceptions code:  There are very small differences in the meat of the
exceptions code, but I think they are related to caching issues?  Other then
that the code that checks to make sure an exception is valid
(mpcxxx_vector_is_valid()) is different in obvious ways, but mostly the same
for the different CPU's

Thats about all the differences there are.  The diff file is not really that
big.  So which of the 2 ports should I use as a base?  Anyone have any

If your wondering what I did to look at the differences, I just diffed the 2
different directories...  I did not miss anything by doing this did I?

My biggest question I think after I get the port started will be related to
the interrupt code stuff, and how do I get it to work from Flash...

Thanks for any help,
Mike Panetta

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