December 5, 2020
By: Kevin
raspberry(linux), clojure (websockt), emacs (cider), (pythoy ble, serial, opencv), etc.
系统架构
- 树莓派端: 作为设备管理器, 开机时候通过websocket和服务器建立连接, 汇报状态
- 服务器端: 一方面为client提供rest接口, 另一方面通过websocket和树莓派通讯, 监控状态, 下发命令, 调用硬件
+--------------------+
| client |
+---------+----------+
|
|
|restful
|
|
+----------+----------+
| |
| web/socket-server |
| |
+----------+----------+
| websocket
+----------------+-----------------+---------------+-------------------+
| | | | |
| | | | |
+----+-----+ +----+----+ +---+----+ +----+-----+ +-----+----+
| pi | | pi | | pi | | pi | | .... |
+----------+ +---------+ +----+---+ +----------+ +----------+
| ble
usb | com
+-----------------+ | +----------------+
| usb cameras +-+-+ height detect |
+-----------------+ | +----------------+
|
+-----+------------+
| mi scale |
+------------------+
树莓派
硬件:
- 开发用的 是raspberry 400(4G内存, 就是那个键盘)
- 部署是用的rasbberry 4b(2G内存, 那块绿色的小板子)
/sshx:pi-work:/home/pi $ lsb_release -a
No LSB modules are available.
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 10 (buster)
Release: 10
系统开发依赖的软件和库
| package | version |
|---------|----------------|
| openjdk | openjdk 11.0.9 |
| clojure | clojure1.10 |
| python | Python 3.7.3 |
| | |
开机自启动
树莓派的应用使用clojure写的,我们要把启动命令写成一个脚本
#!/bin/sh
cd /home/pi/sandbox/rc/new-device/app
lein run
这个脚本放到开机的入口
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
printf "My IP address is %s\n" "$_IP"
fi
su pi -c "exec /home/pi/run-client.sh" # <--- this line make the magic happen.
exit 0;
自动更新
设置系统的cron定时任务, 最小的定时粒度是分钟, 星号是通配符
+-------------------------------------------------------------+
| |
| * * * * * command to be executed |
| - - - - - |
| | | | | | |
| | | | | +----- day of week (0-6) (Sunday=0) |
| | | | +------- month (1-12) |
| | | +--------- day of month (1-31) |
| | +----------- hour (0-23) |
| +------------- minute (0-59) |
| |
| |
+-------------------------------------------------------------+
通过自动拉取git代码, 自动更新.
每分钟git pull一次, 设置好要忽略的文件,保证pull可以成功, 结合重启后的自动运行, 完成了系统升级
远端修改配置&执行脚本
通过特定接口触发配置文件修改
emacs的trampmode
极大方便了开发和调试, 使用emacs tramp功能同时远端调试server和设备
remote server remote raspberry
+--------------+ websocket +-------------+
| service +-------------------------------------+socket client|
+--------------+ +-------------+
| nrepl | | nrepl |
+--------------+ +-------------+
| sshd | | sshd |
+------+-------+ +------+------+
| |
|ssh local dev emacs | ssh
+------+----------------------------------------------------+------+
| ssh |
+------------------------------------------------------------------+
| emacs tramp |
+------------------------------------------------------------------+
| cider projectile etc. |
+------------------------------------------------------------------+
websocket
双向连接始终是一个复杂的话题, socket是一个比较容易接受的方案, 但是socket的使用可以非常复杂.
- socket怎么建立
- 消息队列缓冲
- socket保活
- 断连后恢复
sente 帮我们解决了大部分的socket繁琐底层事务.
摄像头拍照
使用opencv写的python脚本, 抓特定摄像头的输入为图片
import cv2
cam = cv2.VideoCapture(0)
ret, frame = cam.read()
if not ret:
print("failed to grab frame")
else:
img_name = "opencv_frame.png"
cv2.imwrite(img_name, frame)
print("{} written!".format(img_name))
cam.release()
串口通讯
我们系统中使用超声传感器做为身高测量. 这个传感器使用UART串口, 我们使用USB转连
+-----------------+ +-----------------+
| +----------+------------+ |
| raspberry pi | usb port| uart port | sensor |
| +----------+------------+ |
+-----------------+ +-----------------+
usb port和uart port之间通过一个 USB to TTL的设备做转接, 其中的连线方式如下, 注意tx-rx, rx-tx, 即接受端和发送端连接, 发送端和接受端连接.
usb to TTL height detec
+-----------+ +-----------+
| | | |
| | | |
| +5V +--------------------+ VCC |
| | | |
| RX +--------------------+ TX |
| | | |
| TX +--------------------+ RX |
| | | |
| GND +--------------------+ GND | .
| | | |
| 3V3 +--- ---+ OUT |
| | | |
| | | |
| | | |
+-----------+ +-----------+
使用python的串口读取库来做串口的读写通讯
下发指令:0x55 0xaa 0x01 0x01 0x01 checksum 读取数据:0x55 0xAA 0x01 0x01 0x02 0x33 checksum
第5,6位是读到的数据
查看系统现有的串口 python -m serial.tools.list_ports
packet = bytearray()
packet.append(0x55)
packet.append(0xaa)
packet.append(0x01)
packet.append(0x01)
packet.append(0x01)
srial.Serial('/tty/USB0', 9600, timeout=1)
ser.write(packet)
ser_bytes = ser.readall()
distance = struct.unpack('>H', ser_bytes[4:6])
clojure调用脚本
clojure需要调用python脚本实现串口读取, usb摄像头拍照都需要调用shell脚本, sh函数返回被调用脚本执行结果的一个map, 返回状态码, 标准输出stdout, stderr的字符串.
(clojure.java.shell/sh "pwd")
=> {:exit 0,
:out "/Users/kevin/sandbox/rc/new-device/back-end\n",
:err ""}
static scope 和 dynamic scope
静态作用域, 又称为词法作用域 (lexical scope), 这种作用域是我们接触的绝大多数语言的作用域 (Java, C/C++, Python甚至JavaScript).
每个block都有自己的作用域, 子blog的作用域中的变量可以override父级作用域的同名变量, 作用域的规则在编译期间完全决定.
(let [x 1]
(let [x 2]
(prn "inside scope:" x))
(prn "outside scope:" x))
动态作用域是clojure的一个特性, 是一个动态特性 (执行期间)
要理解symbol, var, value
+--------------+------------+------------+
| | | |
(def a 1) -------> | symbol: a | -----------| value: 1 |
| | var | |
+--------------+------------+------------+
#'a is the same as (var a)
实现方式:
- 在声明一个var (def/defn)的时候, 声明为dynamic
(defn ^:dynamic *a* 1). - 线程在执行某段代码时候, 可以使用
(binding [*a* 2] ...)在thread-local中存储变量. - 退出这个block的时候恢复原来的绑定值.
应用场景:
动态控制程序的执行行为, 比如dbeug, 单元测试, 打log等, 比如下面的单元测试固定了执行的硬件版本.
(t/deftest test-vs-cmd
(t/testing "vs-cmd-890"
(binding [state/*hardware-version* (fn [] "890")]
(t/is (=
"01458100000000000000"
(sut/vs->cmd [:v1 :v3 :v7 :v9 :v16] :open))))))
线程的pause和resume
在java中, 实现线程的暂停和继续需要用到wait和notify. Clojure的实现则更简单
(ns httpkit-back-end.util
(:require [clojure.core.async :refer [>!! chan timeout alts!!]]))
(def *msg-record (atom {}))
(defn msg-send [{:keys [device-id msg-type msg-id] :as msg} send-fn]
(let [c (chan)]
(swap! *msg-record assoc-in [device-id msg-type msg-id ] c)
(send-fn)
(let [[msg-body _] (alts!! [(timeout 5000) c])]
(swap! *msg-record dissoc device-id)
msg-body)))
(defn msg-recv [{:keys [device-id msg-type msg-id msg-body]}]
(let [c (get-in @*msg-record [device-id msg-type msg-id])]
(when c
(>!! c msg-body ))))
下面是我们的三个单元测试场景, 分别模拟了正常和超时的情况, 注意到msg-reve都是在一个单独的线程完成的.
(ns httpkit-back-end.util-test
(:require [httpkit-back-end.util :as sut]
[clojure.core.async :refer [thread]]
[clojure.test :as t]))
(t/deftest 收发消息
(t/testing "收发完整流程"
(t/is
(= "100"
(do
(thread
(Thread/sleep 10)
(sut/msg-recv {:device-id 1 :msg-type :a/b :msg-id 123 :msg-body "100"}))
(sut/msg-send {:device-id 1 :msg-type :a/b :msg-id 123} prn)))))
(t/testing "超时时间之内 < 5s"
(t/is
(= "100"
(do
(thread
(Thread/sleep 1000)
(sut/msg-recv {:device-id "1" :msg-type :a/b :msg-id 124 :msg-body "100"}))
(sut/msg-send {:device-id "1" :msg-type :a/b :msg-id 124} prn)))))
(t/testing "超时 > 5s"
(t/is
(nil?
(do
(thread
(Thread/sleep 6000)
(sut/msg-recv {:device-id "1" :msg-type :a/b :msg-id 125 :msg-body "100"}))
(sut/msg-send {:device-id "1" :msg-type :a/b :msg-id 125} prn))))))