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| <section id="eeprom"> |
| <h1>EEPROM<a class="headerlink" href="#eeprom" title="Permalink to this heading"></a></h1> |
| <dl class="simple"> |
| <dt>EEPROMs are a form of Memory</dt><dd><p>Technology Device (MTD). EEPROMs are non-volatile memory like FLASH, but |
| differ in underlying memory technology and differ in usage in many respects: |
| They may not be organized into blocks (at least from the standpoint of the |
| user) and it is not necessary to erase the EEPROM memory before re-writing |
| it. In addition, EEPROMs tend to be much smaller than FLASH parts, usually |
| only a few kilobytes vs megabytes for FLASH. EEPROM tends to be used to |
| retain a small amount of device configuration information; FLASH tends |
| to be used for program or massive data storage. For these reasons, it may |
| not be convenient to use the more complex MTD interface but instead use |
| the simple character interface provided by the EEPROM drivers.</p> |
| </dd> |
| </dl> |
| <section id="eeprom-device-support"> |
| <h2>EEPROM Device Support<a class="headerlink" href="#eeprom-device-support" title="Permalink to this heading"></a></h2> |
| <section id="drivers-eeprom-spi-xx25xx-c"> |
| <h3>drivers/eeprom/spi_xx25xx.c<a class="headerlink" href="#drivers-eeprom-spi-xx25xx-c" title="Permalink to this heading"></a></h3> |
| <p>This is a driver for SPI EEPROMs that use the same commands as the |
| 25AA160:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Manufacturer Device Bytes PgSize AddrLen |
| Microchip |
| 25xx010A 128 16 1 |
| 25xx020A 256 16 1 |
| 25AA02UID 256 16 1 |
| 25AA02E48 256 16 1 |
| 25AA02E64 256 16 1 |
| 25xx040 512 16 1+bit |
| 25xx040A 512 16 1+bit |
| 25xx080 1024 16 1 |
| 25xx080A 1024 16 2 |
| 25xx080B 1024 32 2 |
| 25xx080C 1024 16 x |
| 25xx080D 1024 32 x |
| 25xx160 2048 16 2 |
| 25xx160A/C 2048 16 2 TESTED |
| 25xx160B/D 2048 32 2 |
| 25xx160C 2048 16 2 |
| 25xx160D 2048 32 2 |
| 25xx320 4096 32 2 |
| 25xx320A 4096 32 2 |
| 25xx640 8192 32 2 |
| 25xx640A 8192 32 2 |
| 25xx128 16384 64 2 |
| 25xx256 32768 64 2 |
| 25xx512 65536 128 2 |
| 25xx1024 131072 256 3 |
| Atmel |
| AT25010B 128 8 1 |
| AT25020B 256 8 1 |
| AT25040B 512 8 1+bit |
| AT25080B 1024 32 2 |
| AT25160B 2048 32 2 |
| AT25320B 4096 32 2 |
| AT25640B 8192 32 2 |
| AT25128B 16384 64 2 |
| AT25256B 32768 64 2 |
| AT25512 65536 128 2 |
| AT25M01 131072 256 3 |
| </pre></div> |
| </div> |
| </section> |
| <section id="drivers-mtd-at24xx-c"> |
| <h3>drivers/mtd/at24xx.c<a class="headerlink" href="#drivers-mtd-at24xx-c" title="Permalink to this heading"></a></h3> |
| <p>This is a driver for I2C-based at24cxx EEPROM (at24c32, at24c64, at24c128, |
| at24c256, at24c512). This driver is currently provided as an MTD driver |
| but could easily be modified to support the character driver interface.</p> |
| </section> |
| </section> |
| <section id="file-systems"> |
| <h2>File Systems<a class="headerlink" href="#file-systems" title="Permalink to this heading"></a></h2> |
| <p>Most EEPROM parts are too small to be candidates for use with a file |
| system. The character driver interface is optimal for these small parts |
| because you can open and access the EEPROM part as if it were a single, |
| fixed size file.</p> |
| <p>It is also possible to use these character drivers with a file system. |
| The character driver can converted to a block device using the NuttX loop |
| device. The loop device can be found the file drivers/loop.c. Interface |
| function prototypes can be found in include/nuttx/fs/fs.h:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>int losetup(FAR const char *devname, FAR const char *filename, |
| uint16_t sectsize, off_t offset, bool readonly); |
| </pre></div> |
| </div> |
| <p>Given a file or character devices at ‘filename’, losetup will create the |
| block device ‘devname’ using a bogus sector size of sectsize. ‘offset’ is |
| normally zero but can be used to provide an offset into the EEPROM where |
| the block driver data starts; The EEPROM block driver can also be read- |
| only.</p> |
| <p>There is a corresponding function that will destroy the loop device:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>int loteardown(FAR const char *devname); |
| </pre></div> |
| </div> |
| </section> |
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