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