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 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 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 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 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 {
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gpio-controller; |
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... |
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gpioiic0 { |
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compatible = "gpioiic"; |
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/* |
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* Attach to GPIO pins 21 and 22. Set them |
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* initially as inputs. |
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*/ |
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gpios = <&gpio 21 1 0 |
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&gpio 22 1 0>; |
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scl = <0>; |
/* GPIO pin 21 - optional */ |
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sda = <1>; |
/* GPIO pin 22 - optional */ |
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/* This is an example of a gpioiic child. */ |
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gpioiic-child0 { |
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compatible = "lm75"; |
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i2c-address = <0x4f>; |
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}; |
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}; |
};
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
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.
BSD May 14, 2014 BSD