Hi Darwin,
On Mon, 26 May 2014 09:11:35 -0700, Darwin Rambo drambo@broadcom.com wrote:
Hi Albert,
The previous stage bootloader (which I had no control over) wanted it's header to be aligned to a 512 byte MMC block boundary, presumably since this allowed DMA operations without copy/shifting. At the same time, I didn't want to hack a header into start.S because I didn't want to carry another downstream patch. So I investigated if I could shift u-boot's base address as a feature that would allow an aligned header to be used without the start.S patch.
I know that a custom header patch to start.S would work, and that a header plus padding will also work. But I found out that you can align the base on certain smaller offsets if you keep the relocation offset at nice boundaries like 0x1000 and if the relocation offset is a multiple of the maximum alignment requirements of the image.
The original patch I submitted didn't handle an end condition properly, was ARM64-specific (wasn't tested on other architectures), and because the patch was NAK'd, I didn't bother to submit a v2 patch and consider the idea to be dead. I'm happy to abandon the patch. I hope this helps.
Thanks.
If I understand correctly, your target has a requirement for storing the image on a 512-byte boundary. But how does this affect the loading of the image into RAM, where the requirement is only that the vectors table be 32-bytes aligned? I mean, if you store the image in MMC at offset 0x200 (thus satisfying the 512-byte boundary requirement) and load it to, say, offset 0x10020 in RAM, how is it a problem for your target?
If my example above inadequately represents the issue, then can you please provide a similar but adequate example, a failure case scenario, so that I can hve a correct understanding of the problem?
Best regards, Darwin
Amicalement,