Q on RTEMS for MPC850

[Gunter Magin]

Hi,

On Tue, May 01, 2001 at 03:33:56PM -0400, Janarthanaram Thoguluva wrote:
>     I have a question on supporting RTEMS over MPC850 CPU. I already have 
> an RTEMS-based application running over MPC860. Now, we plan to develop a 
> similar RTEMS-based application but over MPC850 CPU. I wanted to know  if 
> MPC860 and MPC850 are compatible at the instruction level, thereby 
> obviating the need to modifty the RTEMS BSP code.

The PPC core is exactly the same, except caches and TLBs are half the size.
But that will impact performance, not compatibility. In fact, the 850 is a 
stripped down feature limited version of the 860 with a different
pinning. 

What will make it difficult to reuse any 860 BSP is the fact, that the usage
of CPM's parallel pins for special purposes (e.g. SMC TxD, RxD) is
totally different to the 860, so you better double check that part of your
device drivers. And of course, you cannot use SCC3 and SCC4.

Double check mmu setup too, because of different cache/TLB.

gm