On Friday, January 16, 2015 at 07:35:11 PM, Pavel Machek wrote:
Hi!
-#define CONFIG_ENV_IS_NOWHERE
#define CONFIG_ENV_SIZE 4096
+#define CONFIG_ENV_IS_IN_MMC +#define CONFIG_SYS_MMC_ENV_DEV 0/* device 0 */ +#define CONFIG_ENV_OFFSET 512/* just after the MBR */
Would it make sense to make environment bigger (64K?) at this point, and enabling the redundant environment option, so that one bad block does not bring the whole device down?
Do you think you'll ever have more than a 4KiB of text data in the env ? I can see a reason for some 16 KiB environment, but that's the
ceiling.
We have hit 4KiB size already, and I believe we are over 8KiB, even. wagabuibui loads a lot of small files from flash.
So if 16KiB is acceptable, lets do that.
16KiB is fine by me, though I'm not quite sure how you managed to stuff 8KiB full of env ;-)
Usually, the env only has to be a few KiB and it's size has to be multiple of the underlying device's erase block. But in case of SD card, there are no explicit erase blocks exported to the user, all is hidden by the controller in the SD card and gives an illusion of a device which has 512b blocks and
Allocation unit is usually 2, 4, 6, 8, 12 or 16 MiB on recent flash cards. It is field in uSD card structure somewhere. We could choose 24MiB, to have GCD, but... see:
https://wiki.linaro.org/WorkingGroups/KernelArchived/Projects/FlashCardSurv ey
OK, this is even more precise. Thanks for the link.
the user doesn't care for bad block management. Since the controller in the card does the bad block management and wear leveling/relocation of blocks, it also means that in case the controller did fail to provide the block which contains env, the whole card would already be in a very bad state.
Bad block management means you don't get errors during write, but you can still get errors during read.
That in fact depends on the BBM implementation, but in case you get error during read, it's usually a game over kind of situation. But I agree.
Best regards, Marek Vasut