Ronald G Minnich <[EMAIL PROTECTED]> writes:
> On 6 Mar 2001, Eric W. Biederman wrote:
>
> > Theory says that you need to initialize ECC ram to all zeros before any
> > reads occur. In practice this doesn't seem to be needed. I have observed
> > this on both the L440GX and on the alpha DS10.
>
> and besides, the kernel does it for you every time it allocates a page. No
> init needed, except for dogs like dos.
That isn't good enough, to justify it. Only if the SDRAM power up
zero's RAM are we in good shape. With the kernel we can't garantee
we don't get read-modify-write cycles.
I did some tracing of the alpha at power up and it was getting
read-modify-write cycles when the SROM was zeroing RAM, in an attempt
to do the ECC setup properly. And it wasn't getting ECC errors.
I didn't check but the writes are also useless unless you have ECC
enabled at the time you do them.
It is probably worth a look through the SDRAM data sheets to see how
they power up to make certain we are safe.
On x86 we can enable write-combining and doing this a about 600MB/s
with a PII and PC100 SDRAM. But in practice this appears unnecessary...
Eric
