Hi,
On 19-12-14 11:08, Siarhei Siamashka wrote:
On Thu, 18 Dec 2014 19:12:13 +0000
Ian Campbell <i...@hellion.org.uk> wrote:
On Tue, 2014-12-16 at 21:31 +0100, Hans de Goede wrote:
The sun8i boot0 code fills the DRAM with a "random" pattern before comparing
it at different offsets to do columns, etc. detection. The sun6i boot0 code
does not do it, but it seems like a good idea to do this regardless.
Is this the right way round? The existing sun6i code (which you are
moving here) seems to _rely_ on something having written a useful
pattern, which I would have assumed to have been boot0. Or else how does
it work now? Chance?
It appears that this code is just trying to find the first address line,
which is not connected anywhere. If the address line is not connected,
then having the corresponding bit set or clear in the memory address
does not matter and we are effectively accessing the same location.
Correct.
Both sun6i and sun8i code is incorrect and only works because of relying
on luck.
The sun6i code is incorrect because it is just reading memory without
initializing it at all. Probably relying on having some unique garbage
there in a natural way.
The newer sun8i code is still incorrect because it is not safeguarding
against accidentally encountering the same test pattern at an unrelated
memory location. Yes, the probability is extremely low, but still not
zero.
The probability is so low that it really does not matter, so I've no intention
to fix this.
Regards,
Hans
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