[U-Boot-Users] PPC8xx chip select configuration at startup

[Steve Strublic]

Hello all,

 

After a lot of reading of code, FAQs, and this list, I have successfully
ported U-Boot to my custom PowerPC 852T platform.  (And by the way, all
you out there that have problems with SDRAM... make sure your UPM tables
are right; cost me a day for two mistyped values.)  However, I ran into
something that I call unusual, and would like some advice/opinions.  

 

My board boots to address 0x0, with FLASH located there.  The desired
location for FLASH memory will be at 0x0400_0000.  This is the address
space to which I link U-Boot.  The way I understand U-Boot to work is
that for PPC8xx platforms, FLASH memory is generally located at address
0x0, and CS0 is required to map both address 0x0 and your absolute
address space (0x0400_0000 in my example) so it can seamlessly jump from
one to the other.  Later on, when SDRAM needs to be initialized, all
chip selects 0-7 are configured based on definitions in your board's
config include file.

 

Assuming this is correct, I found that my platform would not run past
the jump from address space mapped at 0x0 to address space mapped at
0x0400_0000, and I boiled it down to values in CS0's option register
that are contrary to what I require.  What I ended up doing is program
CS0 base and option registers with what I call 'boot' values, to
correctly configure OR0 to allow this duplication of address space for
FLASH.  This was done immediately prior to the jumpoff point.
Everything from that point on was per normal U-Boot startup (including
the remapping of CS0 later on).  This puts my platform into a known
state that correctly maps all peripheral devices with their proper
sizing and address masks.

 

Is this something uncommon or am I missing something obvious?  Is this
contrary to the goals for U-Boot's architecture at startup of PPC8xx
processors?  Or is this possibly something one would like to see
incorporated into U-Boot?

 

Any advice/comments are appreciated...

 

TIA,

 

Steve

 

------

Steve Strublic

Network Solutions Group

Hypercom Corporation

Phoenix, AZ

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.denx.de/pipermail/u-boot/attachments/20060213/4701ca70/attachment.htm