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JFFS2, unaligned accesses, Arm7Tdmi



Hello, all,

I'm sending this to both uclinux-dev and jffs2-dev because I'm not sure
which is the correct forum... maybe both are!

I am currently using uClinux 2.4.19.uc1 on an Arm7Tdmi family
processor.  I would like to get JFFS2 running on this platform.

On this uClinux CVS snapshot that I am using, I cannot enable MTD
because the arch/armnommu/config.in requires CONFIG_ALIGNMENT_TRAP to
access the mtd/config.in configuration items.
(CONFIG_ALIGNMENT_TRAP appears to be enable-able only for the EBSA1110
platform).

Some searches in Google state that MTD/JFFS2 require processor support
for unaligned accesses.  However, the Arm7Tdmi does not support
unaligned access traps: The processor just clears the corresponding
addresses bits and forces address alignment.  Thus, any attempt to
access data at an unaligned address will just result in
obtaining/writing the wrong data.

This suggests that MTD/JFFS2 would not work with this Arm7 processor?

Now, if I look in the current uClinux CVS, I see that the requirement
for CONFIG_ALIGNMENT_TRAP has been removed from arch/armnommu/config.in
and I could select MTD/JFFS2 without support for unaligned accesses in
that version.

Does anyone know what has changed?  Why unaligned access support is no
longer required?  Does anyone have any recommendations for JFFS2 support
on a processor without unaligned access traps?

Thanks in advance,

Gregory Nutt


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