NAME
gpioiic —
GPIO I2C bit-banging device
driver
SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file:
device gpio
device gpioiic
device iic
device iicbb
device iicbusDESCRIPTION
Thegpioiic driver provides an IIC bit-banging interface
using two GPIO pins for the SCL and SDA on the
gpiobus. gpioiic implements an
open collector kind of output, as recommended by the standard, when driving
the pins on the gpiobus, i.e, they are never switched
to the logical value of '1', or they are '0' or simply open (Hi-Z/tri-state).
So the pullup resistors are required so gpioiic can
work.
On a
device.hints(5) based system, like
MIPS, these values are configurable for the
gpioiic:
- hint.gpioiic.%d.at
- The
gpiobusyou are attaching to. Normally just gpiobus0. - hint.gpioiic.%d.pins
- This is a bitmask of the pins on the
gpiobusthat are to be used for SCLOCK and SDATA from the GPIO IIC bit-banging bus. To configure pin 0 and 7, use the bitmask of 0b10000001 and convert it to a hexadecimal value of 0x0081. Please note that this mask should only ever have two bits set (any other bits - i.e., pins - will be ignored). - hint.gpioiic.%d.scl
- Indicates which bit in the hint.gpioiic.%d.pins should be used as the SCLOCK source. Optional, defaults to 0.
- hint.gpioiic.%d.sda
- Indicates which bit in the hint.gpioiic.%d.pins should be used as the SDATA source. Optional, defaults to 1.
On a FDT(4) based system, like ARM, the
DTS part for a gpioiic device usually looks
like:
gpio: gpio {
gpio-controller;
...
gpioiic0 {
compatible = "gpioiic";
/*
* Attach to GPIO pins 21 and 22. Set them
* initially as inputs.
*/
gpios = <&gpio 21 1 0
&gpio 22 1 0>;
scl = <0>; /* GPIO pin 21 - optional */
sda = <1>; /* GPIO pin 22 - optional */
/* This is an example of a gpioiic child. */
gpioiic-child0 {
compatible = "lm75";
i2c-address = <0x4f>;
};
};
};
Where:
- compatible
- Should always be set to "gpioiic".
- gpios
- The gpios property indicates which GPIO pins should be used for SCLOCK and SDATA on the GPIO IIC bit-banging bus. For more details about the gpios property, please consult /usr/src/sys/dts/bindings-gpio.txt.
- scl
- The scl option indicates which bit in the gpios should be used as the SCLOCK source. Optional, defaults to 0.
- sda
- The sda option indicates which bit in the gpios should be used as the SDATA source. Optional, defaults to 1.
SEE ALSO
HISTORY
The gpioiic manual page first appeared in
FreeBSD 10.1.
AUTHORS
This manual page was written by Luiz Otavio O Souza.