EEPROM: Add a README file

1 files changed, 95 insertions, 0 deletions

diff --git a/nuttx/drivers/eeprom/README.txt b/nuttx/drivers/eeprom/README.txt
new file mode 100755
index 000000000..60938ccf4
--- /dev/null
+++ b/nuttx/drivers/eeprom/README.txt
@@ -0,0 +1,95 @@
+README
+======
+
+  This directory holds simple, EEPROM drivers.  EEPROMs are a form of Memory
+  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.
+
+EEPROM Device Support
+=====================
+
+  drivers/eeprom/spi_xx25xx.c
+  ---------------------------
+  This is a driver for SPI EEPROMs that use the same commands as the
+  25AA160.
+
+    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
+
+  drivers/mtd/at24xx.c
+  ---------------------
+  This is drier for I2C-based at24cxx EEPROM (at24c32 ,at24c64, at24c128,
+  at24c256, at24c512).  This driver driver is currently provided as an
+  MTD driver but could easily be modified to support the character driver
+  interface
+
+File Systems
+============
+
+  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.
+
+  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:
+
+    int losetup(FAR const char *devname, FAR const char *filename,
+                uint16_t sectsize, off_t offset, bool readonly);
+
+  Give 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.
+
+  There is a corresponding function that will destory the loop device:
+
+    int loteardown(FAR const char *devname);