98 lines
4.0 KiB
ReStructuredText
98 lines
4.0 KiB
ReStructuredText
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======
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EEPROM
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======
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EEPROMs are a form of Memory
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Technology Device (MTD). EEPROMs are non-volatile memory like FLASH, but
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differ in underlying memory technology and differ in usage in many respects:
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They may not be organized into blocks (at least from the standpoint of the
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user) and it is not necessary to erase the EEPROM memory before re-writing
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it. In addition, EEPROMs tend to be much smaller than FLASH parts, usually
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only a few kilobytes vs megabytes for FLASH. EEPROM tends to be used to
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retain a small amount of device configuration information; FLASH tends
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to be used for program or massive data storage. For these reasons, it may
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not be convenient to use the more complex MTD interface but instead use
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the simple character interface provided by the EEPROM drivers.
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EEPROM Device Support
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=====================
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drivers/eeprom/spi_xx25xx.c
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---------------------------
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This is a driver for SPI EEPROMs that use the same commands as the
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25AA160::
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Manufacturer Device Bytes PgSize AddrLen
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Microchip
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25xx010A 128 16 1
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25xx020A 256 16 1
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25AA02UID 256 16 1
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25AA02E48 256 16 1
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25AA02E64 256 16 1
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25xx040 512 16 1+bit
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25xx040A 512 16 1+bit
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25xx080 1024 16 1
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25xx080A 1024 16 2
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25xx080B 1024 32 2
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25xx080C 1024 16 x
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25xx080D 1024 32 x
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25xx160 2048 16 2
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25xx160A/C 2048 16 2 TESTED
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25xx160B/D 2048 32 2
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25xx160C 2048 16 2
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25xx160D 2048 32 2
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25xx320 4096 32 2
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25xx320A 4096 32 2
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25xx640 8192 32 2
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25xx640A 8192 32 2
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25xx128 16384 64 2
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25xx256 32768 64 2
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25xx512 65536 128 2
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25xx1024 131072 256 3
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Atmel
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AT25010B 128 8 1
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AT25020B 256 8 1
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AT25040B 512 8 1+bit
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AT25080B 1024 32 2
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AT25160B 2048 32 2
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AT25320B 4096 32 2
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AT25640B 8192 32 2
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AT25128B 16384 64 2
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AT25256B 32768 64 2
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AT25512 65536 128 2
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AT25M01 131072 256 3
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drivers/mtd/at24xx.c
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--------------------
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This is a driver for I2C-based at24cxx EEPROM (at24c32, at24c64, at24c128,
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at24c256, at24c512). This driver is currently provided as an MTD driver
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but could easily be modified to support the character driver interface.
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File Systems
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============
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Most EEPROM parts are too small to be candidates for use with a file
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system. The character driver interface is optimal for these small parts
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because you can open and access the EEPROM part as if it were a single,
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fixed size file.
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It is also possible to use these character drivers with a file system.
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The character driver can converted to a block device using the NuttX loop
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device. The loop device can be found the file drivers/loop.c. Interface
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function prototypes can be found in include/nuttx/fs/fs.h::
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int losetup(FAR const char *devname, FAR const char *filename,
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uint16_t sectsize, off_t offset, bool readonly);
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Given a file or character devices at 'filename', losetup will create the
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block device 'devname' using a bogus sector size of sectsize. 'offset' is
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normally zero but can be used to provide an offset into the EEPROM where
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the block driver data starts; The EEPROM block driver can also be read-
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only.
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There is a corresponding function that will destroy the loop device::
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int loteardown(FAR const char *devname);
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