GPIO

通用输入输出(GPIO)

General Purpose Input/Output (GPIO) pins provide a programmable interface to read the state of a binary input device (such as a pushbutton switch) or control the on/off state of a binary output device (such as an LED).

General Purpose Input/Output (GPIO) 管脚提供了可编程接口用于获取二进制量(如按键开关)的状态或者用于控制二进制输出设备(如发光二级体)的闭/合状态。

You can configure GPIO pins as an input or output with either a high or low state. As an input, an external source determines the state, and your app can read the current value or react to changes in state. As an output, your app configures the state of the pin.

您可以配置GPIO管脚来定义数据传输方向输入或输出高电平或低电平。当管脚做为输入使用时,可以检测到外部信号源的状态变化,您的应用程序可以获得当前状态或者对状态变化做出反应。当管脚做为输出使用时,您的应用程序可以对管脚状态的高低进行配置。

Note: To avoid damage to the GPIO pins, review the input and output limits of your hardware before making wire connections. See Hardware 101 and consult the documentation for your hardware.

注意: 为避免造成对GPIO管脚的损坏,请在对您的硬件进行接线时检查有关GPIO输入和输出的限制。查看硬件 101 并查阅您的硬件的相关文档。

Managing the connection

管理连接


In order to open a connection to a GPIO port, you need to know the unique port name. During the initial stages of development, or when porting an app to new hardware, it's helpful to discover all the available port names from PeripheralManagerService using getGpioList():

当需要对某个GPIO接口进行连接是,您需要获知对应的GPIO端口号。在开发的早期阶段,或者当您在将应用移植到某个新硬件的时候,您可以通过由PeripheralManagerService提供的 getGpioList()来发现所有可用的GPIO端口号:


PeripheralManagerService manager = new PeripheralManagerService();
List<String> portList = manager.getGpioList();
if (portList.isEmpty()) {    
    Log.i(TAG, "No GPIO port available on this device.");
    } else {    
        Log.i(TAG, "List of available ports: " + portList);
}

Once you know the target name, use PeripheralManagerService to connect to that port. When you're done communicating with the GPIO port, close the connection to free up resources. Additionally, you cannot open a new connection to the same port until the existing connection is closed. To close the connection, use the port's close() method.

当您获得了端口名称后,可以使用PeripheralManagerService来连接到这个端口。在您完成对这个GPIO端口的通信后,请记得及时关闭连接以便释放相关资源。另外请注意,对同一个GPIO端口只能建立一个连接,在该连接关闭前您无法再对同一个GPIO端口发起新的连接。如需关闭连接,调用端口的close()方法。

public class HomeActivity extends Activity {    
    // GPIO Pin Name    
    private static final String GPIO_NAME = ...;    
    private Gpio mGpio;    
    @Override    
    protected void onCreate(Bundle savedInstanceState) {        
        super.onCreate(savedInstanceState);        
        // Attempt to access the GPIO        
        try {            
            PeripheralManagerService manager = new PeripheralManagerService();            
            mGpio = manager.openGpio(GPIO_NAME);        
        } catch (IOException e) {             
            Log.w(TAG, "Unable to access GPIO", e);        
        }    
    }    
    @Override    
    protected void onDestroy() {        
        super.onDestroy();        
        if (mGpio != null) {            
            try {                
                mGpio.close();                
                mGpio = null;            
            } catch (IOException e) {                
                Log.w(TAG, "Unable to close GPIO", e);            
            }        
        }    
    }
}

Reading from an input

获得输入


To read a GPIO port as an input:

从某个GPIO端口获得输入:

  1. Configure it as an input using setDirection() with the mode DIRECTION_IN.

    使用setDirection() 方法配置端口的输入方向为DIRECTION_IN

  2. Configure either a high (near IOREF) or low (near zero) voltage signal to be returned as true (active), by calling setActiveType() with ACTIVE_HIGH or ACTIVE_LOW.

    通过配置高电平(接近IOREF)或者低电平(接近零)信号返回为true (使能),并调用setActiveType()方法来相应的配置为ACTIVE_HIGHACTIVE_LOW

  3. Access the current state with the getValue() method.

    通过调用getValue()方法来访问到当前状态。

The following code shows you how to set up an input with an active state associated with a high voltage level:

以下代码为设置GPIO端口的方向为输入并配置使能状态为高电平。


public void configureInput(Gpio gpio) throws IOException {    
    // Initialize the pin as an input    
    gpio.setDirection(Gpio.DIRECTION_IN);    
    // High voltage is considered active    
    gpio.setActiveType(Gpio.ACTIVE_HIGH);    
      // Read the active high pin state    
    if (gpio.getValue()) {        
        // Pin is HIGH    
    } else {        
    // Pin is LOW    
    }
}

Listening for input state changes

获得输入状态的变化

A GPIO port configured as an input can notify your app when its state changes between high and low. To register for these change events:

GPIO端口可以被配置为输入状态时可以在端口状态高低变化时及时通知到您的应用程序。在使用时对如下事件进行注册:

  1. Attach a GpioCallback to the active port connection.

    GpioCallback附加到已经打开的端口连接上。

  2. Declare the state changes that trigger an interrupt event using the setEdgeTriggerType() method. The edge trigger supports the following four types:

    • EDGE_NONE: No interrupt events. This is the default value.
    • EDGE_RISING: Interrupt on a transition from low to high
    • EDGE_FALLING: Interrupt on a transition from high to low
    • EDGE_BOTH: Interrupt on all state transitions

    使用setEdgeTriggerType()方法将状态声明为触发。边沿触发器支持一下四种类型:

    • EDGE_NONE: No interrupt events. This is the default value.
    • EDGE_NONE: 无中断事件. 模式配置.
    • EDGE_RISING: 当从低电平跳变到高电平的上升沿触发中断
    • EDGE_FALLING: 当从高电平下降为低电平的下降沿触发中断
    • EDGE_BOTH: 只要状态变化就触发中断
  3. Return true from within onGpioEdge() to indicate that the listener should continue receiving events for each port state change.

    onGpioEdge()返回为true时,即代表监听程序需要继续接收相关端口的状态变化事件。

The following code registers an interrupt listener for all state changes on the given input port:

如下代码为给定的用于输入的端口注册了相应的中断监听:

public void configureInput(Gpio gpio) throws IOException {    
    // Initialize the pin as an input    
    gpio.setDirection(Gpio.DIRECTION_IN);    
    // Low voltage is considered active    
    gpio.setActiveType(Gpio.ACTIVE_LOW);    
    // Register for all state changes    
    gpio.setEdgeTriggerType(Gpio.EDGE_BOTH);    
    gpio.registerGpioCallback(mGpioCallback);
}

private GpioCallback mGpioCallback = new GpioCallback() {    
    @Override    
        public boolean onGpioEdge(Gpio gpio) {        
            // Read the active low pin state        
            if (gpio.getValue()) {            
                // Pin is LOW        
            } else {            
                // Pin is HIGH        
            }        
            // Continue listening for more interrupts        
            return true;    
        }    
    @Override    
        public void onGpioError(Gpio gpio, int error) {        
            Log.w(TAG, gpio + ": Error event " + error);    
        }
};
  1. Unregister any interrupt handlers when your app is no longer listening for incoming events:

    当您的应用不再对某一GPIO端口的状态变化进行监听时,请及时注销掉相关的中断处理函数。

public class HomeActivity extends Activity {    
    private Gpio mGpio;    
    @Override    
    protected void onStart() {        
        super.onStart();        
        // Begin listening for interrupt events        
        mGpio.registerGpioCallback(mGpioCallback);    
    }    
    @Override    
    protected void onStop() {        
        super.onStop();        
        // Interrupt events no longer necessary        
        mGpio.unregisterGpioCallback(mGpioCallback);    
    }
}

Writing to an output

提供输出


To programmatically control the state of a GPIO port:

通过程序化控制GPIO口的输出状态:

  1. Configure it as an output using setDirection() with the mode DIRECTION_OUT_INITIALLY_HIGH or DIRECTION_OUT_INITIALLY_LOW. These modes ensure that the port's initial state is also set correctly at configuration time.

    通过调用setDirection()方法来配置GPIO的工作方向为输出,其中DIRECTION_OUT_INITIALLY_HIGHDIRECTION_OUT_INITIALLY_LOW参数分别用来配置端口的起始状态的高或低。

  2. Configure either a high (near IOREF) or low (near zero) voltage signal to be returned as true (active), by calling setActiveType() with ACTIVE_HIGH or ACTIVE_LOW.

    通过配置高电平(接近IOREF)或者低电平(接近零)信号返回为true (使能),并调用setActiveType()方法来相应的配置为ACTIVE_HIGHACTIVE_LOW

  3. Set the current state with the setValue() method.

    使用setValue()方法来对当前状态进行设置。

The following code shows you how to set up an output to initially be high, then toggle its state to low using the setValue() method:

以下代码为配置GPIO端口起始状态为高,然后通过调用setValue()方法切换状态为低:

~~~java public void configureOutput(Gpio gpio) throws IOException {
// Initialize the pin as a high output
gpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_HIGH);
// Low voltage is considered active
gpio.setActiveType(Gpio.ACTIVE_LOW);
// Toggle the value to be LOW
gpio.setValue(true); }

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