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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/misc-devices/max6875.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/misc-devices/max6875.rst | 136 |
1 files changed, 136 insertions, 0 deletions
diff --git a/Documentation/misc-devices/max6875.rst b/Documentation/misc-devices/max6875.rst new file mode 100644 index 000000000..ad419ac22 --- /dev/null +++ b/Documentation/misc-devices/max6875.rst @@ -0,0 +1,136 @@ +===================== +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 inputs +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. + |