BSP for MIPS32 4KC

Michael Kelly mike at
Wed Sep 10 17:05:20 UTC 2003

Aaah, there in lies the rub.  MIPS has done a very poor
job of policing it's instruction set architectures (ISA).  Many
of the licensees have taken, well, license, to pick features from
MIPS I, II, III and IV.  For example, we had to compile the
assembly portion of our boot monitor for the Au1500 with
the -mips2 flag by itself, but the C portions with -mips2
and -mcpu=r4600.  As AMD describes it, the Au1 core is
MIPS32 with enhancements.  AFAIK, the enhancements
are mostly in the area of caching, but that's a pretty important


At 12:41 PM 9/10/2003, gregory.menke at wrote:

>mikeci at writes:
> > > Ivica,
> > >
> > > I am about to start a BSP for the AMD Au1500 which is MIPS32
> > > and I wonder if you have any specific details on the context
> > > and interrupt handling changes.  If not, what makes you feel this
> > > will be the case?
> > >
> > > Thanks,
> > > Michael
> > >
> > Michael,
> > 
> > Take look in $RTEMS_HOME/cpukit/score/cpu/mips. There you have cpu.c and
> > cpu_asm.S. Edit cpu_asm.S and search for function _ISR_Handler. You will
> > see that this function returns with:
> > 
> >      j         k1
> >      rfe
> >         NOP
> > 
> >        .set    reorder
> > ENDFRAME(_ISR_Handler)
> > 
> > This is incorrect for MIP32. rfe instruction is reserved for R3000 and not
> > for MIP32.
>Could you please define what MIPS32 is, very explicitely?  By that I
>mean what register width, what cpu family, etc...  
>I still don't know what MIPS32 is other than as a #define!  If its
>R4000 with 32 bit registers, that should be supported right now via
>The j k1, rfe formulation is for R3000, R4000 has its own protocol-
>which is already supported by the cpukit (context switches, etc..).
>At present the R4000 context employs 64 bit registers, but the MIPS
>bsp's are all 32 bits, so I think at present, all MIPS support could
>be shifted to that.

Michael J. Kelly
VP Engineering/Marketing
Cogent Computer Systems, Inc.
1130 Ten Rod Road
Suite A-201
North Kingstown, RI 02852
tel:401-295-6505 fax:401-295-6507
alternate email: mkelly6505 at

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