树莓派 - 通过sysfs操控GPIO

点亮或熄灭LED

硬件上，一个LED灯接在pi的Pin-25.  该引脚为BCM的GPIO26

$ gpio readall
 +-----+-----+---------+------+---+---Pi 3---+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 |     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
 |   2 |   8 |   SDA.1 | ALT0 | 1 |  3 || 4  |   |      | 5v      |     |     |
 |   3 |   9 |   SCL.1 | ALT0 | 1 |  5 || 6  |   |      | 0v      |     |     |
 |   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | ALT5 | TxD     | 15  | 14  |
 |     |     |      0v |      |   |  9 || 10 | 1 | ALT5 | RxD     | 16  | 15  |
 |  17 |   0 | GPIO. 0 |   IN | 0 | 11 || 12 | 1 | IN   | GPIO. 1 | 1   | 18  |
 |  27 |   2 | GPIO. 2 |   IN | 0 | 13 || 14 |   |      | 0v      |     |     |
 |  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
 |     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
 |  10 |  12 |    MOSI |   IN | 0 | 19 || 20 |   |      | 0v      |     |     |
 |   9 |  13 |    MISO |   IN | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
 |  11 |  14 |    SCLK |   IN | 0 | 23 || 24 | 1 | IN   | CE0     | 10  | 8   |
 |     |     |      0v |      |   | 25 || 26 | 1 | IN   | CE1     | 11  | 7   |
 |   0 |  30 |   SDA.0 |   IN | 1 | 27 || 28 | 1 | IN   | SCL.0   | 31  | 1   |
 |   5 |  21 | GPIO.21 |   IN | 1 | 29 || 30 |   |      | 0v      |     |     |
 |   6 |  22 | GPIO.22 |   IN | 1 | 31 || 32 | 0 | IN   | GPIO.26 | 26  | 12  |
 |  13 |  23 | GPIO.23 |   IN | 0 | 33 || 34 |   |      | 0v      |     |     |
 |  19 |  24 | GPIO.24 |   IN | 0 | 35 || 36 | 0 | IN   | GPIO.27 | 27  | 16  |
 |  26 |  25 | GPIO.25 |  OUT | 0 | 37 || 38 | 0 | IN   | GPIO.28 | 28  | 20  |
 |     |     |      0v |      |   | 39 || 40 | 0 | IN   | GPIO.29 | 29  | 21  |
 +-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
 | BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
 +-----+-----+---------+------+---+---Pi 3---+---+------+---------+-----+-----+├

按照下面的命令点亮及熄灭LED

pi@raspberrypi:/sys/class/gpio $echo 26 > export

pi@raspberrypi:/sys/class/gpio $ cd gpio26
pi@raspberrypi:/sys/class/gpio/gpio26 $ ls
active_low  device  direction  edge  power  subsystem  uevent  value
pi@raspberrypi:/sys/class/gpio/gpio26 $ cat direction
out
pi@raspberrypi:/sys/class/gpio/gpio26 $ cat value
1
pi@raspberrypi:/sys/class/gpio/gpio26 $ echo 0 >value
pi@raspberrypi:/sys/class/gpio/gpio26 $ cat value
0

sysfs

Linux 2.6以后的内核引入了sysfs文件系统， sysfs被看作是与proc, devfs和devpty同类别的文件系统。该文件系统是一个虚拟的文件系统，它可以产生一个包括所有系统硬件的层级视图。

sysfs把连接在系统上的设备和总线组织成一个分级的文件，它可以由用户空间存取， 向用户空间导出内核数据结构以及他们的属性。

其顶层目录包括， block, bus, dev, devices, class, fs, kernel, power 和firmware

从下面的bus, devices, class中对应的gpiochip1, 可以看到Linux设备模型与总线，设备，驱动，类的状态是对应的。

在linux内核中分别使用bus_type, device_driver, device来描述总线，驱动和设备。

device_driver和device分别表示驱动和设备，这两者都必须依附于一种总线，因此都包含struct bus_type指针。

/sys/bus

pi@raspberrypi:/sys/bus $ tree

├── gpio
│   ├── devices
│   │   ├── gpiochip0 -> ../../../devices/platform/soc/3f200000.gpio/gpiochip0
│   │   ├── gpiochip1 -> ../../../devices/gpiochip1
│   │   └── gpiochip2 -> ../../../devices/gpiochip2
│   ├── drivers
│   ├── drivers_autoprobe
│   ├── drivers_probe
│   └── uevent

/sys/devices

pi@raspberrypi:/sys/devices $ tree | more

├── gpiochip1
│   ├── dev
│   ├── gpio
│   │   └── gpiochip128
│   │       ├── base
│   │       ├── device -> ../../../gpiochip1
│   │       ├── label
│   │       ├── ngpio
│   │       ├── power
│   │       │   ├── autosuspend_delay_ms
│   │       │   ├── control
│   │       │   ├── runtime_active_time
│   │       │   ├── runtime_status
│   │       │   └── runtime_suspended_time
│   │       ├── subsystem -> ../../../../class/gpio
│   │       └── uevent
│   ├── of_node -> ../../firmware/devicetree/base/soc/expgpio
│   ├── power
│   │   ├── autosuspend_delay_ms
│   │   ├── control
│   │   ├── runtime_active_time
│   │   ├── runtime_status
│   │   └── runtime_suspended_time
│   ├── subsystem -> ../../bus/gpio
│   └── uevent

/sys/class

pi@raspberrypi:/sys/class $ tree

├── gpio
│   ├── export
│   ├── gpio26 -> ../../devices/platform/soc/3f200000.gpio/gpiochip0/gpio/gpio26
│   ├── gpiochip0 -> ../../devices/platform/soc/3f200000.gpio/gpio/gpiochip0
│   ├── gpiochip100 -> ../../devices/gpiochip2/gpio/gpiochip100
│   ├── gpiochip128 -> ../../devices/gpiochip1/gpio/gpiochip128
│   └── unexport