[U-Boot-Users] Data Chache enable
Jerry Van Baren
gerald.vanbaren at smiths-aerospace.com
Tue May 2 19:55:12 CEST 2006
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
> I am new to this.
> Thank you,
Exception 0200 is Machine Check, it has nothing directly to do with data
caching except for the fact that you are enabling data cache
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
More information about the U-Boot