MMU problems on Linux 8xx. (reliability...)

Lucinda Schafer lucsch at
Tue Jun 20 02:29:42 EST 2000

Are you using a standard or custom board? Our MPC823-based custom board
crashes occasionally on a page fault or other memory management related
routine. We always get the kernel mode FPU software emulation panic. It
seems that you are experiencing the same problem as we are.

It is interesting that you see this work on a PPC750 but not PPC823. Dan
states that there are no instructions that are not supported by the 823
implemented in the Linux kernel; but a problem with the 32 TLB versus 8(??)
hasn't been addressed, although that seems too obvious.

We are very frustrated at this point, as we are working towards a
manufacturable product. A kernel panic is not acceptable--it's a show

We are going to go back to the BSE-IP board and run similar tests on both
the Monta Vista and standard, patched kernels, (2.2.13) to "see" if it's
related to our hardware and/or the kernel we are running.

Any suggestions are welcome.

Lucinda Schafer
Staff Software Engineer
Adaptive Micro-Ware, Inc.

-----Original Message-----
From: Patrick Lerda [mailto:Lerda at]
Sent: Wednesday, June 14, 2000 4:11 AM
To: 'linuxppc-embedded at'
Subject: MMU problems on Linux 8xx. (reliability...)

I've a PPC823 board working with a recent linux kernel based on monta vista.
When I try complex operation like compiling a kernel on this board, the
crash after a while. An illegal instruction is generated, linux see
an opcode: *NIP=0, the illegal instruction occur in a glibc-2.1.3 page.
The glibc page is not see properly... This problem seems to occur
only on complex operation, and make this system not reliable.

I also have a PPC750 board working with the same kernel with proper
the only differences in code is the MMU part. Linux work properly and
on this board with the PPC860 software.

if you have see a similar behaviour on you boards, or with differents
I know that the PPC823 is not 100% compatible with the PPC860, there is
some differences on TLB available etc... And linux seems to be hard coded
for 32 TLB...

If you know how the MMU is handle on linux 8xx, and if you see a similar
let me know...

Patrick LERDA

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