IBM PPC750L vs Motorola MPC7410

IBM PPC750L vs Motorola MPC7410

[Peter Dennett]

I have some SBS CK3 boards which can mount
either a IBM PPC750L or Motorola MPC7410.
There is a architecture variant for MontaVista
(older Hard Hat - SBS "K2") for the MPC7410
and I have been running it.  I have reason to switch
to the IBM part (it is known to be radiation tolerant
for space applications).

When I use the same boot image on the PPC750L
the system hangs during the bootstrap process.
(transfers to common routine to decompress the
kernel, reports successful decompress, then no
more serial output).

I don't come from the PPC world and do not know
the lineage of these chips - in fact don't know the difference
between G3 and G4...

Is there someone on this list that can be so kind as to give
me a technical summary of the differences between the
PPC750L (G3) and Motorola MPC7410 (G4) so far as
LINUX operation.

I assume some portions of the low level setup (cache,
memory, serial port, ...) are different between the two
chips.  I can ferret out and fix it, but I would rather like
to avoid becoming a complete expert on both parts...

TIA

Peter Dennett   Office: 281 334 3800  Cell: 713 899 6100
pdennett@padsoft.com                www.padsoft.com
pdennett@boatbrains.com           www.boatbrains.com


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Re: IBM PPC750L vs Motorola MPC7410

[Chris Zimman]

On Wed, Jul 16, 2003 at 09:33:37AM -0500, Peter Dennett wrote:
> When I use the same boot image on the PPC750L
> the system hangs during the bootstrap process.
> (transfers to common routine to decompress the
> kernel, reports successful decompress, then no
> more serial output).
>
> I don't come from the PPC world and do not know
> the lineage of these chips - in fact don't know the difference
> between G3 and G4...
>
> Is there someone on this list that can be so kind as to give
> me a technical summary of the differences between the
> PPC750L (G3) and Motorola MPC7410 (G4) so far as
> LINUX operation.

I would suggest you get an architecture manual for both.  You
may be able to find a working kernel image for the 750, but
the PPC family isn't quite as nuclear as the x86 for example.
At least from a low level perspective, what works on one PPC chip
may not necessarily work on another.

If you want the simple answer, just build a kernel image that's
appropriate for your board and processor and use that.

> I assume some portions of the low level setup (cache,
> memory, serial port, ...) are different between the two
> chips.  I can ferret out and fix it, but I would rather like
> to avoid becoming a complete expert on both parts...

Cache setup is going to be different.  Some parts of memory setup,
but most SDRAM setup is done in the host bridge anyway.  The
serial port code has nothing to do with the CPU.

--Chris

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Re: IBM PPC750L vs Motorola MPC7410

[Paul Mackerras]

Peter Dennett writes:

> Is there someone on this list that can be so kind as to give
> me a technical summary of the differences between the
> PPC750L (G3) and Motorola MPC7410 (G4) so far as
> LINUX operation.

The biggest difference is that the 7410 has Altivec and the 750
doesn't.  Altivec is an extension to the instruction set that adds 32
128-bit registers plus a set of SIMD-style operations on those
registers.

Beyond that there will be differences in the special-purpose registers
(SPRs) accessible in kernel mode.  I don't think there would be
enormous difference but there would be some.

The kernel should detect which CPU you have and do the right thing
automatically.  Neither chip has an on-chip memory controller or
serial port; both have on-chip L1 I and D cache and on-chip L2 cache
controller and tag RAM (if I recall correctly).  So I don't know why
the kernel would hang when booting the G3.

Paul.


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