172 lines
4.3 KiB
Groff
172 lines
4.3 KiB
Groff
.\" Copyright (c) 2013, Luiz Otavio O Souza <loos@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 13, 2014
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.Dt GPIOIIC 4
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.Os
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.Sh NAME
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.Nm gpioiic
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.Nd GPIO I2C bit-banging device driver
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following lines in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device gpio"
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.Cd "device gpioiic"
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.Cd "device iic"
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.Cd "device iicbb"
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.Cd "device iicbus"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver provides an IIC bit-banging interface using two GPIO pins for the
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SCL and SDA on the
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.Nm gpiobus .
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.Nm
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implements an open collector kind of output, as recommended by the standard,
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when driving the pins on the
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.Nm gpiobus ,
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i.e, they are never switched to the logical value of '1',
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or they are '0' or simply open (Hi-Z/tri-state).
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So the pullup resistors are required so
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.Nm
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can work.
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.Pp
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On a
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.Xr device.hints 5
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based system, like
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.Li MIPS ,
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these values are configurable for the
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.Nm :
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.Bl -tag -width ".Va hint.gpioiic.%d.atXXX"
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.It Va hint.gpioiic.%d.at
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The
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.Nm gpiobus
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you are attaching to.
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Normally just gpiobus0.
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.It Va hint.gpioiic.%d.pins
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This is a bitmask of the pins on the
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.Nm gpiobus
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that are to be used for SCLOCK and SDATA from the GPIO IIC
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bit-banging bus.
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To configure pin 0 and 7, use the bitmask of
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0b10000001 and convert it to a hexadecimal value of 0x0081.
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Please note that this mask should only ever have two bits set
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(any other bits - i.e., pins - will be ignored).
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.It Va hint.gpioiic.%d.scl
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Indicates which bit in the
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.Va hint.gpioiic.%d.pins
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should be used as the SCLOCK
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source.
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Optional, defaults to 0.
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.It Va hint.gpioiic.%d.sda
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Indicates which bit in the
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.Va hint.gpioiic.%d.pins
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should be used as the SDATA
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source.
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Optional, defaults to 1.
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.El
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.Pp
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On a
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.Xr FDT 4
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based system, like
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.Li ARM ,
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the DTS part for a
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.Nm gpioiic
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device usually looks like:
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.Bd -literal
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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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};
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};
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.Ed
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.Pp
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Where:
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.Bl -tag -width ".Va compatible"
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.It Va compatible
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Should always be set to "gpioiic".
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.It Va gpios
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The
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.Va gpios
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property indicates which GPIO pins should be used for SCLOCK and SDATA
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on the GPIO IIC bit-banging bus.
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For more details about the
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.Va gpios
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property, please consult
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.Pa /usr/src/sys/boot/fdt/dts/bindings-gpio.txt .
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.It Va scl
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The
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.Va scl
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option indicates which bit in the
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.Va gpios
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should be used as the SCLOCK source.
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Optional, defaults to 0.
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.It Va sda
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The
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.Va sda
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option indicates which bit in the
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.Va gpios
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should be used as the SDATA source.
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Optional, defaults to 1.
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.El
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.Sh SEE ALSO
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.Xr fdt 4 ,
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.Xr gpio 4 ,
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.Xr gpioled 4 ,
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.Xr iic 4 ,
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.Xr iicbb 4 ,
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.Xr iicbus 4
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.Sh HISTORY
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The
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.Nm
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manual page first appeared in
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.Fx 11.0 .
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.Sh AUTHORS
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This
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manual page was written by
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.An Luiz Otavio O Souza .
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