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4f7fc3dd04
Also fix some minor issues in the DS2XXX header file. Signed-off-by: Stepan Pressl <pressl.stepan@gmail.com>
135 lines
4.6 KiB
ReStructuredText
135 lines
4.6 KiB
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================
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One Wire Drivers
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================
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---------------------------------------------------------------
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Interfacing multiple devices of the same family on the same bus
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---------------------------------------------------------------
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1Wire is a bus and thus the driver should allow to specify the device the application
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should interface. Also the driver should allow to scan the whole bus for available devices.
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The proper way should involve a background thread continuously scanning the bus and possibly
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registering them in a filesystem.
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But this would probably too much of an overkill, and thus a much simpler solution is to
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call a scanning ``ioctl``, obtain available devices, select the one we want and tell that
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to the driver.
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.. c:macro:: ONEWIREIOC_GETFAMILYROMS
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An ``ioctl`` call that returns all scanned devices' ROMs of the same family
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(the family depends on the driver). All of the records are stored
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to the ``struct onewire_availroms_s`` object (supplied by the application).
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Usage: ``ioctl(fd, ONEWIREIOC_GETFAMILYROMS, (unsigned long *)&query)``
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.. c:struct:: onewire_availroms_s
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.. code-block:: c
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struct onewire_availroms_s
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{
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uint64_t *roms;
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int maxroms;
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int actual;
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};
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The number of maximum records the driver can provide is specified by the user
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in the ``maxroms`` field. The user must also specify the ``uint64_t`` buffer
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into the ``roms`` field where the driver can store the scanned devices.
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The number of scanned devices is set in the ``actual`` field by the driver.
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.. c:macro:: ONEWIREIOC_SETROM
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Set the ROM of the device the driver should interface. Please note the
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ROM argument is a pointer to a ``uint64_t`` variable, and not a ``uint64_t``
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value, the reason being ``arg`` in ``ioctl`` is ``unsigned long``, which
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is 32bits on many architectures.
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Usage: ``ioctl(fd, ONEWIREIOC_SETROM, (unsigned long *)&romcode)``.
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-----------------------------------------
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Maxim/Analog Devices DS2XXX EEPROM driver
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-----------------------------------------
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This driver can be used to interface the following EEPROMS with a scratchpad
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(also specified in ``enum ds2xxx_eeproms_e`` in ``include/nuttx/1wire/1wire_ds2xxx.h``):
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- DS2430: 32 bytes, 8 byte scratchpad,
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- DS2431: 128 bytes, 8 byte scratchpad,
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- DS2432: 128 bytes, 8 byte scratchpad,
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- DS2433: 512 bytes, 32 byte scratchpad,
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- DS28E04: 512 bytes, 32 byte scratchpad,
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- DS28E07: 128 bytes, 8 byte scratchpad,
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- DS28EC20: 2560 bytes, 32 byte scratchpad.
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Each driver's instance can interface only one EEPROM type. If you want to interface
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multiple eeproms on the same bus, you need to have two drivers (e.g. two ``/dev`` files).
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Currently, only basic read/write operations on the EEPROMs are implemented.
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Special ioctl calls locking respective pages (or possibly any other EEPROM features)
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are still not yet implemented.
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As the EEPROM driver is character based, you can move around the EEPROM using ``lseek``.
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Scratchpad unaligned reads and writes are possible.
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Driver's API
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============
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.. c:enum:: ds2xxx_eeproms_e
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.. code-block:: c
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enum ds2xxx_eeproms_e
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{
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EEPROM_DS2430 = 0,
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EEPROM_DS2431,
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EEPROM_DS2432,
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EEPROM_DS2433,
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EEPROM_DS28E04,
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EEPROM_DS28E07,
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EEPROM_DS28EC20,
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EEPROM_DS_COUNT
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};
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The enum of all supported EEPROMS (besides ``EEPROM_DS_COUNT``).
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.. c:function:: int ds2xxx_initialize(FAR struct onewire_dev_s *dev, enum ds2xxx_eeproms_e devtype, FAR char *devname)
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Bind a ``onewire_dev_s`` struct to this driver, capable of interfacing
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DS2XXX 1Wire EEPROMs. The user must specify the device type
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and also the name of the device (e.g. ``/dev/ds2xxx``).
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:param dev: a pointer to the lowerhalf struct
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:param devtype: the type of EEPROMs to be interfaced
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:param devname: the name of the registered file
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:return: 0 on success and a registered driver, negated errno on failure
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Example usage
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-------------
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Registering a driver (STM32 BSP, DS2431 memory):
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.. code-block:: c
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struct onewire_dev_s *lwhalf;
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lwhalf = stm32_1wireinitialize(0);
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ds2xxx_initialize(lwhalf, EEPROM_DS2431, "/dev/ds2431");
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Application usage (suppose all calls are successful):
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.. code-block:: c
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/* Write to a specific EEPROM */
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int fd = open("/dev/ds2xxx", O_RDWR);
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struct onewire_availroms_s query;
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uint64_t romarr[8];
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query.roms = romarr;
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query.maxroms = 8;
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ioctl(fd, ONEWIREIOC_GETFAMILYROMS, (unsigned long *)&query);
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/* Suppose the driver returns 3 in query.actual. We want the last
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* device to be accessed.
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*/
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ioctl(fd, ONEWIREIOC_SETROM, (unsigned long *)&query.roms[query.actual - 1]);
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lseek(fd, 10, SEEK_SET);
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write(fd, "HELLO", 5);
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