[U-Boot-Users] uboot newbie - tqm823 and memory conf question
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:
> > 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
> - 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
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
More information about the U-Boot