On Fri, 17 Sep 2010 22:47:04 +0200 Wolfgang Denk wd@denx.de wrote:
For example, on NOR flash we might see an erase block size of 256 KiB (resulting in a "#define CONFIG_ENV_SECT_SIZE (256 << 10)" or similar). But normally we don't need so much space for the environment, so we set CONFIG_ENV_SIZE to (for example) 16 KiB. The advantage is that with this setting the checksum calculation includes only CONFIG_ENV_SIZE, which can be a measurable difference in boot time.
The largest NAND page size that I'm aware of is 8 KiB (with 2 or 4 KiB currently being more common), so it's not as burdensome a restriction -- and NOR flash doesn't have the concept of a NAND-style page; you can write a word at a time.
However, I was looking at the master branch when I wrote that. I forgot that in my next branch, I have a patch that removes this requirement (there was existing read-modify-write code, but it was blocked by an unnecessary check in nand_do_write_ops). :-)
I'll respin the README patch.
-Scott