On flash NVS was stored one entry after another including the metadata
of each entry. This has the disadvantage that when an incomplete write
is performed (e.g. due to power failure) the complete sector had to be
rewritten to get a completely functional system.
The present rewrite changed the storage in flash of the data. For each
sector the data is now written as follows: the data itself at the
beginning of the sector (one after the other), the metadata (id, length,
data offset in the sector, and a crc of the metadata) is written from
the end of the sector. The metadata is of fixed size (8 byte) and for
a sector that is completely occupied a metadata entry of all zeros is
used.
Writing data to flash always is done by:
1. Writing the data,
2. Writing the metadata.
If an incomplete write is done NVS will ignore this incomplete write.
At the same time the following improvements were done:
1. NVS now support 65536 sectors of each 65536 byte.
2. The sector size no longer requires to be a power of 2 (but it
still needs to be a multiple of the flash erase page size).
3. NVS now also keeps track of the free space available.
Signed-off-by: Laczen JMS <laczenjms@gmail.com>
The nvs module has some disadvantages for larger block size. The data
header and slot are taking up to much space. A rewrite is proposed that
reduces the used storage space for systems with write block size > 4.
The data storage in flash is now one unit consisting of: data_length,
data_id, data and data_length again in a multiple of the write block
size. The data_length at the end is used to validate the correctness of
the flash write and also allows to travel backwards in the filesystem.
As a comparison, on a system with block size 8 byte, a 32 bit values
now fits 1 block including the metadata (length and id). This used to
be 3 blocks.
The data_length will occupy 1 byte if the data length is less than 128
byte, it will occupy 2 byte if the data length is 128 byte or more. The
data length is limited to 16383 byte.
Each write to flash is verified by a read back of the data.
The read performance is improved because reading is done backwards so
the latest items are found first.
When the filesystem is locked it can be unlocked by calling
reinit(), this will clear flash and setup everything for storage.
add sample documentation - README.rst
Update dtsi to include erase_block_size, use erase_block_size in sample
Update prj.conf to include CONFIG_MPU_ALLOW_FLASH_WRITE
Signed-off-by: Laczen JMS <laczenjms@gmail.com>
The two functions that compute the crc16 when writing (nvs_append_close)
and when reading (nvs_check_crc) currently assume that the flash is
also mapped in read mode at address 0. This is not true on all SoCs, and
even less on an SPI flash.
Fix this by adding a new nvs_compute_crc() function which compute the
CRC16 of an entry using the flash using nvs_flash_read, in blocks of
write_block_size. This might not be the optimal size, but it keeps the
stack usage small.
Use this function in both nvs_append_close() and nvs_check_crc() instead
of accessing the flash from address 0.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Now that the flash writes are padded up to the write block size, there
is no need to have explicit padding fields in the _nvs_sector_hdr and
_nvs_data_slt structure. This allow to save space when the write block
size equals to 1 or 2
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Zephyr supports fatfs, nffs and fcb as storage layer. fatfs and nffs
are less suited for application in memory restricted IC's. fcb has a
smaller footprint but has a complex api.
The proposed module is a module with a even smaller footprint compared
to fcb and a simple interface for reading and writing entries. The
module provides wear levelling of flash. This allows the module to be
used not only to store configuration settings but to store device state
(e.g. state of a light switch over reboots) of a zephyr device.
Fixes buffer overflow by introducing maximum read length in nvs_read()
and nvs_read_hist().
Fixes nvs_write() not to reflash the same data. Allows the user to do
call nvs_write() for all defined entries without worries about flash
wear.
Fixes garbage collection error where wrong data could be copied.
Add nvs_delete() to allow deleting a stored entry. A deleted entry will
not be copied to a new flash sector
Include flash wear information in the README.md documentation
0/25 Update module after reviewers remarks, added documentation to
nvs.h, removed README.md by nvs.rst in doc/subsystems folder
04/26 Update module after reviewers remarks, updated nvs.rst, added more
documentation to samples/subsys/nvs/src/main.c, updated doxygen info
in nvs.h (hope this time it works).
04/26 Update subsystems.rst to include nvs.restart
04/27 Updated nvs.c and nvs.h to avoid a possible flash deletion loop
when the file system is full.
04/29 Updated nvs_write to detect and ignore deletes of non-existing
items
05/06 Update NVS module to return standard error codes, removed low
level API, added configuration options. NVS now uses the board dts to
determine the flash storage location (FLASH_AREA_STORAGE_OFFSET).
05/06 Update nvs.rst. Updated intendation and added intermediate
variables in nvs.c to make the code easier to read.
05/06 Update nvs.rst.
05/07 Update nvs.rst
05/08 Changed the API to a more standard file system API.
05/08 Removed cnt_max from nvs_read() as it is not used.
05/08 Removed #ifdef(CONFIG_NVS_LOG) from nvs_priv.h, now the module can
be build with debugging off.
05/09 Removed configuration options for SECTOR_SIZE, SECTOR_COUNT and
MAX_ELEM_SIZE. It is now easy to support multiple NVS filesystems on
one or multiple devices. Changed logging to support newlib systems.
Thanks to Olivier Martin for reporting and proposed changes.
Signed-off-by: Laczen JMS <laczenjms@gmail.com>
Laczen JMS