[U-Boot-Users] uboot newbie - tqm823 and memory conf question

Wolfgang Denk wd at denx.de
Mon Feb 17 23:20:23 CET 2003

In message <Pine.LNX.4.44.0302171146460.7989-100000 at loki.aehr.com> you wrote:
> Thanks!

You're welcome.

> > So depending if you have CAN on your modules or  not  you  can  chose
> > form CS4...CS7 or from CS3...CS7.
> >
> Well then, how does the CPU "know" about that area?

Ummm... please read the  memory  controller  section  of  the  MPC8xx
User's Manual.

> Meaning:
> - Is the Address area on that bus the actual physical range the CPU sees?


> - Or, does it get mapped into the CPUs physical space via configuration?


> - How does the CPU know, that it is SRAM or something else?

It doesn't know, and it doesn't need to know. It  just  goes  through
the  memory  controller registers to find a BRx/ORx pair that matches
the physical address, and  then  it  accesses  the  corresponding  CS
according to the other params in BRx/ORx.

Not that the scanning always starts at  BR0/OR0,  so  if  you  define
overlapping memory regions always the first one will win.

> OK, I need to setup the mem controller.


> I will search in the source there.

What for? Just add it to your Linux device driver's init() code.

> Is that then still possible to change the mem controller setup when the
> kernel is already coming up?? I hope so!

It is. You can change it any time you like. There are  several  cases
wher  eit  is  changed on the fly (for example, some of the FPGA boot
commands in U-Boot will mdify the memory controller  programming  for
the load operation of the FPGA(s), and return to the "normal" setting

Viele Grüße,
Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
See us @ Embedded World, Nuremberg, Feb 18-20, Hall 12.0 Booth 12-442

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