Booting Linux from an ACE File

[Stephen Neuendorffer]

> -----Original Message-----
> From: linuxppc-embedded-bounces+stephen=neuendorffer.name at ozlabs.org
[mailto:linuxppc-embedded-
> bounces+stephen=neuendorffer.name at ozlabs.org] On Behalf Of mojtaba
> Sent: Friday, May 16, 2008 4:58 AM
> To: linuxppc-embedded at ozlabs.org
> Subject: Booting Linux from an ACE File
> 
> Dear all,
> 
> Could you please explain what happens exactly when Linux is booting
from a
> compact flash?

The systemAce file is essentially a script of JTAG commands, some of
which target the FPGA with configuration data and some target the
PowerPC/microblaze with memory write commands.

> To my few knowledge, the Linux compressed image will be copied
somewhere in
> memory, will be uncompressed and the control will jump to the
beginning
> address of the Linux kernel.
> 
> Is there any boot loader that copies the Linux compressed image to the
> memory?

Essentially SystemAce does this for you and jumps to the Linux
bootwrapper code which begins decompressing the kernel.

> Where in memory does it put the Linux kernel? For example, if I have 2
DDRs
> in my hardware, in which of them it will be put the kernel?

The kernel is compiled at a particular address, typically targetting
whatever memory is low in the system.  I believe the default target
address is 0x40000.  So whatever DDR memory lives at this address will
be targetted.

> Can I set the kernel location in memory manually?

If you change how the bootwrapper code and linker script work, yes.

> Might be an stupid question but: Is it possible for the kernel to be
half in
> BRAMS and half in DDR?

There have been some recent patches on the microblaze mailing lists that
attempt to put some of the latency-critical code (exception handlers and
the like) in BRAM.  Doing this is likely pretty architecture specific,
since you probably have a particular goal in mind.

Steve

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