[U-Boot-Users] Data Chache enable

[Jerry Van Baren]

PDF conversion wrote:
> Processor: MPC8260
> U-boot Version: 1.1.2
> Project: Communication SDH
> 
> I am trying to avoid the D chache exception 200 when I
> enable D cache. 
> 
> I know that the documentation indicates: "Data cache
> cannot be enabled on systems like 8xx or 8260(where
> access to IMMR region must be uncached). D cache
> cannot be diabled on other systems where we (mis-)use
> d-cache to hold an initial stach & some data..."
> 
> Are there any new commands I can include in the U-Boot
> boot loader?
> 
> Does any one know what the specific register settings
> are to avoid the data cache exception. 
> 
> If there is any documentation I overlooked please
> indicate. 
> 
> I am new to this.
> 
> Thank you,
> Regards,
> 
>  -Om

Exception 0200 is Machine Check, it has nothing directly to do with data 
caching except for the fact that you are enabling data cache 
inappropriately.

The simplest way to use data cache the way you appear to want to use it 
is to use the BATs to map your I/O memory (minimum: IMMR region) as 
uncached and the rest of your used memory (flash + RAM) as cached.  If 
you don't do that, _everything_ is cached which is a Very Bad Thing[tm], 
as you found out.  I am not aware of anybody having success enabling 
data cache without BATs/MMUs and successfully maintaining cache 
coherency by hand (which is what you are hinting at).

You didn't answer Wolfgang's question "Why do you want to enable data 
cache in u-boot???"  Normally there no need to do that, so you are 
either doing something very unusual or you don't understand the problem 
you are trying to solve.  If you tell us the problem, we might be able 
to give better advice (or at least tell you why we are saying "don't do 
that").

gvb