[ECOS] why scrub memory?

[Mark Salter]

No. eCos/RedBoot makes no assumption that memory is cleared (except for
.bss of course). Caches will sometimes cause memory to be read before
it is written. Also, the scrub writes have to be 64-bit writes. Otherwise
it could be a read-modify-write cycle on the bus.

--Mark


>>>>> Aaron Richardson writes:

> This seems reasonable enough... however, isnt all memory that is going to be 
> used written to before it is used?  Does Ecos/Redboot assume that the memory 
> has been written with zeros when it uses memory?

> thanks,
> Aaron


> On Friday 20 June 2003 02:38 pm, Mark Salter wrote:
>> >>>>> Aaron Richardson writes:
>> >
>> > I see on several platforms (including the one that I am working on) that
>> > memory scrubbing is occuring.  Why is this done and can I remove it?  I
>> > am tired of waiting the time for this occur.  I have 256 MB of memory
>> > right now, but plan on having much more in the future.
>> 
>> When the ECC memory is first powered on, it must be written to
>> before it is read. This syncs the ECC code bits with the data
>> bits. The simplest approach is taken and all of memory is
>> scrubbed before any is used. If the application that RedBoot
>> boots (or the standalone eCos app) is not going to muck with
>> the MMU, then the HAL could be enhanced to defer scrubbing a
>> given memory page until that page is first touched. But only
>> if that's not a performance problem for the app.
>> 
>> --Mark

> -- 


> Aaron Richardson
> aarichar@cisco.com
> 512-378-1286



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