云中树莓派（3）：通过 AWS IoT 控制树莓派上的 Led

1. Led 连接与测试

在某宝上买了几样配件，包括T型GPIO扩展板、40P排线、亚克力外壳、400孔面包板、若干杜邦线。现在我的树莓派长得这个样子了：

不由得感谢神奇的某宝，这些东西每一样都不超过三四块钱。

1.1 接线

以下几个简单步骤就完成了接线：

将排线一头插在树莓派的40个pin脚上，将另一头插在扩展板上。要注意方向，多试几次。还要注意在树莓派关机时候再插入。
把扩展板插在面包板上。
把Led 的长脚（正极）插在面包板第6行的任何一个孔内（对应GPIO18），将其短脚（负极或接地）插在第7行的任何一个孔内（对应GND）。

简单说下面包板。刚拿到手时还有点不知所措，稍微研究一下后就简单了。面包板为长方形，长边的两边是为了接电源的，每个长边都是联通的；中间区域内，每行内是联通的。

1.2 简单测试

下面的 python 能让led 灯每两秒钟亮一次：

import RPi.GPIO as GPIO

import time

PIN_NO=18

GPIO.setmode(GPIO.BCM)

GPIO.setup(PIN_NO, GPIO.OUT)

loopCount = 0

for x in xrange(500):

    print("Loop " + str(loopCount))

    GPIO.output(PIN_NO, GPIO.HIGH)

    time.sleep(2)

    GPIO.output(PIN_NO, GPIO.LOW)

    time.sleep(2)

    loopCount += 1

GPIO.cleanup()

也就是通过控制GPIO18的电压为高还是低来控制Led 灯是亮还是灭。

2. AWS IoT Device Shadow

AWS IoT 中一个功能叫做 Device Shadow，翻译为『设备影子』。它本质上为用于存储和检索设备的当前状态信息的 JSON 文档。Device Shadow 服务可以为您连接到 AWS IoT 的每台设备保留一个影子。您可以使用该影子通过 MQTT 或 HTTP 获取和设置设备的状态，无论该设备是否连接到 Internet。每台设备的影子都由相应事物的名称唯一标识。Device Shadow 服务充当中介，支持设备和应用程序检索和更新设备的影子。

AWS IoT 针对设备的影子提供了三项操作：

UPDATE：如果设备的影子不存在，则创建一个该影子；如果存在，则使用请求中提供的数据更新设备的影子的内容。存储数据时使用时间戳信息，以指明最新更新时间。向所有订阅者发送消息，告知 desired 状态与 reported 状态之间的差异 (增量)。接收到消息的事物或应用程序可以根据 desired 状态和 reported 状态之间的差异执行操作。例如，设备可将其状态更新为预期状态，或者应用程序可以更新其 UI，以反映设备状态的更改。
GET：检索设备的影子中存储的最新状态 (例如，在设备启动期间，检索配置和最新操作状态)。此操作将返回整个 JSON 文档，其中包括元数据。
DELETE：删除设备的影子，包括其所有内容。这将从数据存储中删除 JSON 文档。您无法还原已删除的设备的影子，但可以创建具有相同名称的新影子。

也就是说，要通过 AWS IoT 来操作设备，需要通过设备影子进行。下图是控制Led 灯泡的示意图。外部应用和设备之间的交互通过设备影子进行。

Device Shadow 使用系统预留的 MQTT 主题来做应用程序和设备之间的通信：

MQTT 主题	用途
$aws/things/myLightBulb/shadow/update/accepted	当设备的影子更新成功时，Device Shadow 服务将向此主题发送消息
$aws/things/myLightBulb/shadow/update/rejected	当设备的影子更新遭拒时，Device Shadow 服务将向此主题发送消息
$aws/things/myLightBulb/shadow/update/delta	当检测到设备的影子的“reported”部分与“desired”部分之间存在差异时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/get/accepted	当获取设备的影子的请求获批时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/get/rejected	当获取设备的影子的请求遭拒时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/delete/accepted	当设备的影子被删除时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/delete/rejected	当删除设备的影子的请求遭拒时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/update/documents	每次设备的影子更新成功执行时，Device Shadow 服务都会向此主题发布状态文档。

下图显示了控制流程：

连接着的 Led 灯发送封装在MQTT消息中的 reported 状态『off』到 AWS IoT
AWS IoT 通过 led 灯使用的证书来确定它所属的虚拟事物
AWS IoT 将 reported 状态保存在设备影子 JSON 文件中
一条 AWS IoT rule 正监控着 led 的 off 状态，它发送一个消息到某个 SNS topic
某 application 收到 SNS 消息。用户将 led 期望状态（desired state）设置为 on
AWS IoT 收到该消息，它更新设备影子中的 desired state，同时发送包含期望状态的 message 到某些topic。此时，reported 和 desired 状态是『Out of Sync』的
led 收到 delta 消息，开始根据其中的 desired status 来设置其实际状态
led 将其状态设置为 on，向 MQTT topic 发送新的 reported 状态
AWS IoT 更新设备影子，现在该设备的 reported 和 desired 状态一致了

3. Python 代码

代码一共就两个文件。文件 ledController.py 充当Led 灯的控制器，它定期向Led 发出『开』或『关』的指令，并定期获取其状态；文件 ledSwitch.py 充当 Led 等的操纵器，它通过调用树莓派的 GPIO 接口来设置和获取 led 灯的状态，以及将其状态上报给 IoT 服务。

AWS IoT 提供了 Device Shadow python SDK，因此不需要直接操作各种 MQTT 主题，而可以使用 get，update 和 delete 这种API。其地址在 https://github.com/aws/aws-iot-device-sdk-python/tree/master/AWSIoTPythonSDK/core/shadow。

3.1 ledController.py

from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient

import logging

import time

import json

import threading

# Led shadow JSON Schema

#

#

# Name: Led

# {

#     "state: {

#               "desired": {

#                          "light": <on|off>

#                }

#      }

#}

deviceShadowHandler = None

def getDeviceStatus():

    while True:

        print("Getting device status...\n")

        deviceShadowHandler.shadowGet(customShadowCallback_get, 50)

        time.sleep(60)    

def customShadowCallback_get(payload, responseStatus, token):

    if responseStatus == "timeout":

        print("Get request with token " + token + " time out!")

    if responseStatus == "accepted":

        print("========== Printing Device Current Status =========")

        print(payload)

        payloadDict = json.loads(payload)

        #{"state":{"desired":{"light":0},"reported":{"light":100}

        try:

            desired = payloadDict["state"]["desired"]["light"]

            desiredTime = payloadDict["metadata"]["desired"]["light"]["timestamp"]

        except Exception:

            print("Failed to get desired state and timestamp.")

        else:

            print("Desired status: " + str(desired) + " @ " + time.ctime(int(desiredTime)))

        try:

            reported = payloadDict["state"]["reported"]["light"]

            #"metadata":{"desired":{"light":{"timestamp":1533893848}},"reported":{"light":{"timestamp":1533893853}}}

            reportedTime = payloadDict["metadata"]["reported"]["light"]["timestamp"]

        except Exception:

            print("Failed to get reported time or timestamp")

        else:

            print("Reported status: " + str(reported) + " @ " + time.ctime(int(reportedTime)))

        print("=======================================\n\n")

    if responseStatus == "rejected":

        print("Get request with token " + token + " rejected!")

def customShadowCallback_upate(payload, responseStatus, token):

    # payload is a JSON string which will be parsed by jason lib

    if responseStatus == "timeout":

        print("Update request with " + token + " time out!")

    if responseStatus == "accepted":

        playloadDict = json.loads(payload)

        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")

        print("Update request with token: " + token + " accepted!")

        print("light: " + str(playloadDict["state"]["desired"]["light"]))

        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n")

    if responseStatus == "rejected":

        print("Update request " + token + " rejected!")

def customShadowCallback_delete(payload, responseStatus, token):

    if responseStatus == "timeout":

        print("Delete request " + token + " time out!")

    if responseStatus == "accepted":

        print("Delete request with token " + token + " accepted!")

    if responseStatus == "rejected":

        print("Delete request with token " + token + " rejected!")

# Cofigure logging

logger = logging.getLogger("AWSIoTPythonSDK.core")

logger.setLevel(logging.ERROR)

streamHandler = logging.StreamHandler()

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

streamHandler.setFormatter(formatter)

logger.addHandler(streamHandler)

# AWS IoT Core endpoint. Need change some values to yours.

awsiotHost = "**********.iot.*********.amazonaws.com"

awsiotPort = 8883;

# AWS IoT Root Certificate. Needn't change.

rootCAPath = "/home/pi/awsiot/VeriSign-Class3-Public-Primary-Certification-Authority-G5.pem"

# Device private key. Need change to yours.

privateKeyPath = "/home/pi/awsiot/aec2731afd-private.pem.key"

# Device certificate. Need change to yours.

certificatePath = "/home/pi/awsiot/aec2731afd-certificate.pem.crt"

myAWSIoTMQTTShadowClient = None;

myAWSIoTMQTTShadowClient = AWSIoTMQTTShadowClient("RaspberryLedController")

myAWSIoTMQTTShadowClient.configureEndpoint(awsiotHost, awsiotPort)

myAWSIoTMQTTShadowClient.configureCredentials(rootCAPath, privateKeyPath, certificatePath)

myAWSIoTMQTTShadowClient.configureAutoReconnectBackoffTime(1, 32, 20)

myAWSIoTMQTTShadowClient.configureConnectDisconnectTimeout(60) # 10sec

myAWSIoTMQTTShadowClient.configureMQTTOperationTimeout(50) #5sec

#connect to AWS IoT

myAWSIoTMQTTShadowClient.connect()

#create a devcie Shadow with persistent subscription

thingName = "homepi"

deviceShadowHandler = myAWSIoTMQTTShadowClient.createShadowHandlerWithName(thingName, True)

#Delete shadow JSON doc

deviceShadowHandler.shadowDelete(customShadowCallback_delete, 50)

#start a thread to get device status every 5 seconds

statusLoopThread = threading.Thread(target=getDeviceStatus)

statusLoopThread.start()

#update shadow in a loop

loopCount = 0

while True:

    desiredState = "off"

    if (loopCount % 2 == 0):

        desiredState = "on"

    print("To change Led desired status to \"" + desiredState + "\" ...\n")

    jsonPayload = '{"state":{"desired":{"light":"' + desiredState + '"}}}'

    print("payload is: " + jsonPayload + "\n")

    deviceShadowHandler.shadowUpdate(jsonPayload, customShadowCallback_upate, 60)

    loopCount += 1

    time.sleep(60)

3.2 ledSwitch.py

import RPi.GPIO as GPIO

from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient

import logging

import time

import json

# Led shadow JSON Schema

#

#

# Name: Led

# {

#     "state: {

#               "desired": {

#                          "light": <on|off>

#                }

#      }

#}

LED_PIN_NUM = 18 # GPIO Number of Led long pin. Change to yours.

deviceShadowHandler = None

#initialize GOPI

GPIO.setmode(GPIO.BCM)

GPIO.setup(LED_PIN_NUM, GPIO.OUT)

def customShadowCallback_Delta(payload, responseStatus, token):

    # payload is a JSON string which will be parsed by jason lib

    print(responseStatus)

    print(payload)

    payloadDict = json.loads(payload)

    print("++++++++ Get DELTA data +++++++++++")

    desiredStatus = str(payloadDict["state"]["light"])

    print("desired status: " + desiredStatus)

    print("version: " + str(payloadDict["version"]))

    #get device current status

    currentStatus = getDeviceStatus()

    print("Device current status is " + currentStatus)

    #udpate device current status

    if (currentStatus != desiredStatus):

        # update device status as desired

        updateDeviceStatus(desiredStatus)

        # send current status to IoT service

        sendCurrentState2AWSIoT()

    print("+++++++++++++++++++++++++++\n")

def updateDeviceStatus(status):

    print("=============================")

    print("Set device status to " + status)

    if (status == "on"):

        turnLedOn(LED_PIN_NUM)

    else:

        turnLedOff(LED_PIN_NUM)

    print("=============================\n")

def getDeviceStatus():

    return getLedStatus(LED_PIN_NUM)

def turnLedOn(gpionum):

    GPIO.output(gpionum, GPIO.HIGH)

def turnLedOff(gpionum):

    GPIO.output(gpionum, GPIO.LOW)

def getLedStatus(gpionum):

    outputFlag = GPIO.input(gpionum)

    print("outputFlag is " + str(outputFlag))

    if outputFlag:

        return "on"

    else:

        return "off"    

def sendCurrentState2AWSIoT():

    #check current status of device

    currentStatus = getDeviceStatus()

    print("Device current status is " + currentStatus)

    print("Sending reported status to MQTT...")

    jsonPayload = '{"state":{"reported":{"light":"' + currentStatus + '"}}}'

    print("Payload is: " + jsonPayload + "\n")

    deviceShadowHandler.shadowUpdate(jsonPayload, customShadowCallback_upate, 50)

def customShadowCallback_upate(payload, responseStatus, token):

    # payload is a JSON string which will be parsed by jason lib

    if responseStatus == "timeout":

        print("Update request with " + token + " time out!")

    if responseStatus == "accepted":

        playloadDict = json.loads(payload)

        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")

        print(payload)

        print("Update request with token: " + token + " accepted!")

        print("light: " + str(playloadDict["state"]["reported"]["light"]))

        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n")

    if responseStatus == "rejected":

        print("Update request " + token + " rejected!")

def customShadowCallback_Get(payload, responseStatus, token):

    print("responseStatus: " + responseStatus)

    print("payload: " + payload)

    payloadDict = json.loads(payload)

    # {"state":{"desired":{"light":37},"delta":{"light":37}},"metadata":{"desired":{"light":{"timestamp":1533888405}}},"version":54

    stateStr = ""

    try:

        stateStr = stateStr + "Desired: " + str(payloadDict["state"]["desired"]["light"]) + ", "

    except Exception:

        print("No desired state")

    try:

        stateStr = stateStr + "Delta: " + str(payloadDict["state"]["delta"]["light"]) + ", "

    except Exception:

        print("No delta state")

    try:

        stateStr = stateStr + "Reported: " + str(payloadDict["state"]["reported"]["light"]) + ", "

    except Exception:

        print("No reported state") 

    print(stateStr + ", Version: " + str(payloadDict["version"]))

def printDeviceStatus():

    print("=========================")

    status = getDeviceStatus()

    print(" Current status: " + str(status))

    print("=========================\n\n")

# Cofigure logging

logger = logging.getLogger("AWSIoTPythonSDK.core")

logger.setLevel(logging.DEBUG)

streamHandler = logging.StreamHandler()

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

streamHandler.setFormatter(formatter)

logger.addHandler(streamHandler)

awsiotHost = "***********.iot.********.amazonaws.com"

awsiotPort = 8883;

rootCAPath = "/home/pi/awsiot/VeriSign-Class3-Public-Primary-Certification-Authority-G5.pem"

privateKeyPath = "/home/pi/awsiot/aec2731afd-private.pem.key"

certificatePath = "/home/pi/awsiot/aec2731afd-certificate.pem.crt"

myAWSIoTMQTTShadowClient = None;

myAWSIoTMQTTShadowClient = AWSIoTMQTTShadowClient("RaspberryLedSwitch")

myAWSIoTMQTTShadowClient.configureEndpoint(awsiotHost, awsiotPort)

myAWSIoTMQTTShadowClient.configureCredentials(rootCAPath, privateKeyPath, certificatePath)

myAWSIoTMQTTShadowClient.configureAutoReconnectBackoffTime(1, 32, 20)

myAWSIoTMQTTShadowClient.configureConnectDisconnectTimeout(60) # 10sec

myAWSIoTMQTTShadowClient.configureMQTTOperationTimeout(30) #5sec

#connect to AWS IoT

myAWSIoTMQTTShadowClient.connect()

#create a devcie Shadow with persistent subscription

thingName = "homepi"

deviceShadowHandler = myAWSIoTMQTTShadowClient.createShadowHandlerWithName(thingName, True)

#listen on deleta

deviceShadowHandler.shadowRegisterDeltaCallback(customShadowCallback_Delta)

#print the intital status

printDeviceStatus()

#send initial status to IoT service

sendCurrentState2AWSIoT()

#get the shadow after started

deviceShadowHandler.shadowGet(customShadowCallback_Get, 60)

#update shadow in a loop

loopCount = 0

while True:

    time.sleep(1)

3.3 主要过程

（1）ledSwitch.py 在运行后，获取led 的初始状态，并将其发给 AWS IoT 服务：

=========================

 outputFlag is 0

 Current status: off

=========================

outputFlag is 0

Device current status is off

Sending reported status to MQTT...

Payload is: {"state":{"reported":{"light":"off"}}}

（2）ledController.py 开始运行后，它首先获取led 的当前状态，为『off』

（3）Controller 将其 desired 状态设置为 on

To change Led desired status to "on" ...

payload is: {"state":{"desired":{"light":"on"}}}

（4）Switch 收到 DELTA 消息，调用 GPIO 接口设置其状态，并向 IOT 服务报告其状态

{"version":513,"timestamp":1533983956,"state":{"light":"on"},"metadata":{"light":{"timestamp":1533983956}},"clientToken":"93dfc84c-c9f9-49fb-b844-d55203991208"}

++++++++ Get DELTA data +++++++++++

desired status: on

version: 513

outputFlag is 0

Device current status is off

=============================

Set device status to on

=============================

outputFlag is 1

Device current status is on

Sending reported status to MQTT...

Payload is: {"state":{"reported":{"light":"on"}}}

（5）Controller 获取最新状态

{"state":{"desired":{"light":"on"},"reported":{"light":"on"}},"metadata":{"desired":{"light":{"timestamp":1533983956}},"reported":{"light":{"timestamp":1533983957}}},"version":514,"timestamp":1533983959,"clientToken":"f24bcbbb-4b24-4354-b1df-349afdf23422"}

Desired status: on @ Sat Aug 11 18:39:16 2018

Reported status: on @ Sat Aug 11 18:39:17 2018

（6）循环往复

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