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$FreeBSD: stable/10/share/man/man4/gpioiic.4 266106 2014-05-15 01:37:17Z loos $
.Dd May 14, 2014 .Dt GPIOIIC 4 .Os .Sh NAME .Nm gpioiic .Nd GPIO I2C bit-banging device driver .Sh SYNOPSIS .Cd "device gpio" .Cd "device gpioiic" .Cd "device iic" .Cd "device iicbb" .Cd "device iicbus" .Sh DESCRIPTION The .Em gpioiic driver provides an IIC bit-banging interface using two GPIO pins for the SCL and SDA on the .Em gpiobus . .Nm implements an open colector kind of output, as recommended by the standard, when driving the pins on the .Em 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 .Nm can work.
p On a hint based system, like .Li MIPS , these values are configureable for the .Nm gpioiic : l -tag -width ".Va hint.gpioiic.%d.atXXX" t Va hint.gpioiic.%d.at The gpiobus you are attaching to. Normally just gpiobus0. t Va hint.gpioiic.%d.pins This is a bitmask of the pins on the .Em 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). t Va hint.gpioiic.%d.scl Indicates which bit in the .Va hint.gpioiic.%d.pins should be used as the SCLOCK source. Optional, defaults to 0. t Va hint.gpioiic.%d.sda Indicates which bit in the .Va hint.gpioiic.%d.pins should be used as the SDATA source. Optional, defaults to 1. .El
p On a .Xr FDT 4 based system, like .Li ARM , the dts part for a .Nm gpioiic device usually looks like: d -literal 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>; }; }; }; .Ed
p Where: l -tag -width ".Va compatible" t Va compatible Should always be set to "gpioiic". t Va gpios The .Va 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 .Va gpios property, please consult
a /usr/src/sys/boot/fdt/dts/bindings-gpio.txt . t Va scl The .Va scl option indicates which bit in the .Va gpios should be used as the SCLOCK source. Optional, defaults to 0. t Va sda The .Va sda option indicates which bit in the .Va gpios should be used as the SDATA source. Optional, defaults to 1. .El .Sh SEE ALSO .Xr fdt 4 , .Xr gpio 4 , .Xr gpioled 4 , .Xr iic 4 , .Xr iicbb 4 , .Xr iicbus 4 .Sh HISTORY The .Nm manual page first appeared in .Fx 10.1 . .Sh AUTHORS This manual page was written by .An Luiz Otavio O Souza .