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authorArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2010-09-28 10:47:06 +0300
committerArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2010-09-28 10:47:06 +0300
commit94a20240f9d6776619d7652013bb10131ddad1fc (patch)
treee92336c72820e7c6daa8468913fbcc523968d257 /ubi-utils/old-utils/UBI.TXT
parent351ac23f8d468b2b9bc60dfcbaacbe3d55ec11f9 (diff)
ubi-utils: remove old ubi-utils
The utilities are unmaintained for long time, and many of them do not even work, just compile, and no on complains about this. This suggests they are unused and we can now safely kill them. Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
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-UBI - Unsorted Block Images
-
-UBI (Latin: "where?") manages multiple logical volumes on a single
-flash device, specifically supporting NAND flash devices. UBI provides
-a flexible partitioning concept which still allows for wear-levelling
-across the whole flash device.
-
-In a sense, UBI may be compared to the Logical Volume Manager
-(LVM). Whereas LVM maps logical sector numbers to physical HDD sector
-numbers, UBI maps logical eraseblocks to physical eraseblocks.
-
-More information may be found in the UBI design documentation:
-ubidesign.pdf. Which can be found here:
-http://www.linux-mtd.infradead.org/doc/ubi.html
-
-Partitioning/Re-partitioning
-
- An UBI volume occupies a certain number of erase blocks. This is
- limited by a configured maximum volume size, which could also be
- viewed as the partition size. Each individual UBI volume's size can
- be changed independently of the other UBI volumes, provided that the
- sum of all volume sizes doesn't exceed a certain limit.
-
- UBI supports dynamic volumes and static volumes. Static volumes are
- read-only and their contents are protected by CRC check sums.
-
-Bad eraseblocks handling
-
- UBI transparently handles bad eraseblocks. When a physical
- eraseblock becomes bad, it is substituted by a good physical
- eraseblock, and the user does not even notice this.
-
-Scrubbing
-
- On a NAND flash bit flips can occur on any write operation,
- sometimes also on read. If bit flips persist on the device, at first
- they can still be corrected by ECC, but once they accumulate,
- correction will become impossible. Thus it is best to actively scrub
- the affected eraseblock, by first copying it to a free eraseblock
- and then erasing the original. The UBI layer performs this type of
- scrubbing under the covers, transparently to the UBI volume users.
-
-Erase Counts
-
- UBI maintains an erase count header per eraseblock. This frees
- higher-level layers (like file systems) from doing this and allows
- for centralized erase count management instead. The erase counts are
- used by the wear-levelling algorithm in the UBI layer. The algorithm
- itself is exchangeable.
-
-Booting from NAND
-
- For booting directly from NAND flash the hardware must at least be
- capable of fetching and executing a small portion of the NAND
- flash. Some NAND flash controllers have this kind of support. They
- usually limit the window to a few kilobytes in erase block 0. This
- "initial program loader" (IPL) must then contain sufficient logic to
- load and execute the next boot phase.
-
- Due to bad eraseblocks, which may be randomly scattered over the
- flash device, it is problematic to store the "secondary program
- loader" (SPL) statically. Also, due to bit-flips it may become
- corrupted over time. UBI allows to solve this problem gracefully by
- storing the SPL in a small static UBI volume.
-
-UBI volumes vs. static partitions
-
- UBI volumes are still very similar to static MTD partitions:
-
- * both consist of eraseblocks (logical eraseblocks in case of UBI
- volumes, and physical eraseblocks in case of static partitions;
- * both support three basic operations - read, write, erase.
-
- But UBI volumes have the following advantages over traditional
- static MTD partitions:
-
- * there are no eraseblock wear-leveling constraints in case of UBI
- volumes, so the user should not care about this;
- * there are no bit-flips and bad eraseblocks in case of UBI volumes.
-
- So, UBI volumes may be considered as flash devices with relaxed
- restrictions.
-
-Where can it be found?
-
- Documentation, kernel code and applications can be found in the MTD
- gits.
-
-What are the applications for?
-
- The applications help to create binary flash images for two
- purposes: pfi files (partial flash images) for in-system update of
- UBI volumes, and plain binary images, with or without OOB data in
- case of NAND, for a manufacturing step. Furthermore some tools
- are/and will be created that allow flash content analysis after a
- system has crashed.
-
-Who did UBI?
-
- The original ideas, where UBI is based on, were developed by Andreas
- Arnez, Frank Haverkamp and Thomas Gleixner. Josh W. Boyer and
- some others were involved too. The implementation of the kernel
- layer was done by Artem B. Bityutskiy. The user-space applications
- and tools were written by Oliver Lohmann with contributions from
- Frank Haverkamp, Andreas Arnez, and Artem. Joern Engel contributed a
- patch which modifies JFFS2 so that it can be run on a UBI
- volume. Thomas Gleixner did modifications to the NAND layer and also
- some to JFFS2 to make it work.