Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / Documentation / misc-devices / max6875

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+Kernel driver max6875
+=====================
+
+Supported chips:
+  * Maxim MAX6874, MAX6875
+    Prefix: 'max6875'
+    Addresses scanned: None (see below)
+    Datasheet:
+        http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
+
+Author: Ben Gardner <bgardner@wabtec.com>
+
+
+Description
+-----------
+
+The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
+It provides timed outputs that can be used as a watchdog, if properly wired.
+It also provides 512 bytes of user EEPROM.
+
+At reset, the MAX6875 reads the configuration EEPROM into its configuration
+registers.  The chip then begins to operate according to the values in the
+registers.
+
+The Maxim MAX6874 is a similar, mostly compatible device, with more intputs
+and outputs:
+             vin     gpi    vout
+MAX6874        6       4       8
+MAX6875        4       3       5
+
+See the datasheet for more information.
+
+
+Sysfs entries
+-------------
+
+eeprom        - 512 bytes of user-defined EEPROM space.
+
+
+General Remarks
+---------------
+
+Valid addresses for the MAX6875 are 0x50 and 0x52.
+Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
+The driver does not probe any address, so you explicitly instantiate the
+devices.
+
+Example:
+$ modprobe max6875
+$ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
+
+The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
+addresses.  For example, for address 0x50, it also reserves 0x51.
+The even-address instance is called 'max6875', the odd one is 'dummy'.
+
+
+Programming the chip using i2c-dev
+----------------------------------
+
+Use the i2c-dev interface to access and program the chips.
+Reads and writes are performed differently depending on the address range.
+
+The configuration registers are at addresses 0x00 - 0x45.
+Use i2c_smbus_write_byte_data() to write a register and
+i2c_smbus_read_byte_data() to read a register.
+The command is the register number.
+
+Examples:
+To write a 1 to register 0x45:
+  i2c_smbus_write_byte_data(fd, 0x45, 1);
+
+To read register 0x45:
+  value = i2c_smbus_read_byte_data(fd, 0x45);
+
+
+The configuration EEPROM is at addresses 0x8000 - 0x8045.
+The user EEPROM is at addresses 0x8100 - 0x82ff.
+
+Use i2c_smbus_write_word_data() to write a byte to EEPROM.
+
+The command is the upper byte of the address: 0x80, 0x81, or 0x82.
+The data word is the lower part of the address or'd with data << 8.
+  cmd = address >> 8;
+  val = (address & 0xff) | (data << 8);
+
+Example:
+To write 0x5a to address 0x8003:
+  i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
+
+
+Reading data from the EEPROM is a little more complicated.
+Use i2c_smbus_write_byte_data() to set the read address and then
+i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
+
+Example:
+To read data starting at offset 0x8100, first set the address:
+  i2c_smbus_write_byte_data(fd, 0x81, 0x00);
+
+And then read the data
+  value = i2c_smbus_read_byte(fd);
+
+  or
+
+  count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
+
+The block read should read 16 bytes.
+0x84 is the block read command.
+
+See the datasheet for more details.
+