NAME¶
gpioiic
—
GPIO I2C bit-banging device driver
SYNOPSIS¶
device gpio
device gpioiic
device iic
device iicbb
device iicbus
DESCRIPTION¶
The
gpioiic driver provides an IIC bit-banging
interface using two GPIO pins for the SCL and SDA on the
gpiobus.
gpioiic
implements an open colector 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 hint based system, like
MIPS
,
these values are configureable for the
gpioiic
:
- hint.gpioiic.%d.at
- The gpiobus you are attaching to. Normally just gpiobus0.
- hint.gpioiic.%d.pins
- This is a bitmask of the pins on the gpiobus
that 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 others 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/boot/fdt/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¶
fdt(4),
gpio(4),
gpioled(4),
iic(4),
iicbb(4),
iicbus(4)
HISTORY¶
The
gpioiic
manual page first appeared in
FreeBSD 10.1.
AUTHORS¶
This manual page was written by
Luiz Otavio O
Souza.