Hi,
On 19-12-14 11:08, Siarhei Siamashka wrote:
On Thu, 18 Dec 2014 19:12:13 +0000 Ian Campbell ijc@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