1.
IOT感測器驅動程式
在樹莓派上實作
翁O謙 丁O傑 王O斌
王O忠 吳O霖 張O晃
陳O陽

2.
專題動機
• 在物聯網的應用領域中，感知層是物聯網發展的基礎，依各種場景的需要會
使用到不同的感測器來收集資訊，但每種感測器要能在嵌入式系統上正常運
作，都需要由驅動程式來驅動，所以開發或移植驅動程式算是嵌入式系統必
備的技術，因此幾位對Linux驅動程式有興趣的同學決定一起開發感測器驅動
程式，並將此感測器拿來做物聯網的應用。

3.
系統架構圖
電子羅盤
距離感測器
Cloud
Web Application
溫度：27 ℃
濕度 : 59 %
距離：212 cm
X：200
Y：191
Z：-351
GPIO
GPIO
I2C
溫溼度感測器

4.
感測器驅動程式的實現
1.溫濕度感測器(DHT22)驅動程式
2.距離感測器(HC-SR04)驅動程式
3.電子羅盤(GY-273)驅動程式
DHT22
Driver
HCSR04
Driver
GY273
Driver
GPIO
GPIO
IIC
DHT22
HCSR04
GY273
KernelChar
/dev/dht22
/dev/hcsr04
/dev/gy237

5.
Linux驅動程式運作流程
driver_init()
cdev_init()
gpio_i2c_setup()
interrupt_setup()
timer_setup()
device_open()
device_read()
- Trigger_Sensor
- Interrup_Irq
- Data_Analysis
device_close()
File Operations driver_exit()
cdev_exit()
gpio_i2c_free()
interrupt_free()
timer_cancel()
insmod Application rmmod
User Space
Kernel Space

6.
Process_data() {
for( n = 0; n < 40; n++)
if(high_time[n] > 50us)
data_bit[n] = 1;
else
data_bit[n] = 0;
…
dht22_irq_handler() {
irq_counter++;
now = get_time();
if(gpio == low)
high_time[] = now – pre;
if(irq_counter == last)
WORK_QUEUE(process_data());
pre = now;
}
2-1 Linux Driver for DHT22
dht22的通訊機制：
DHT22
DHT22 signal
> 1 ms
dht22_trigger() {
gpio_set_direction(pin, out);
gpio_set_value(pin, low);
udelay(1000);
gpio_set_value(pin, high);
udelay(20);
gpio_set_direction(pin, in);
}
Interrup_setup() {
reuest_irq(pin,
dht22_irq_handler,
FALLING_And_RISING)
}
Hi_H Lo_H Hi_T Lo_T Checksum
Work_Queue
Humidity
= Hi_H x 256 + Lo_H
Temperature
= Hi_T x 256 + Lo_T
Checksum
= Hi_H + Lo_H + Hi_T + Lo_T
Trigger 40-Bit DataResponse
1. interrup_setup
2. trigger
3. interrup_irq
4. process_data

7.
2-1 Linux Driver for DHT22
Ready
for
Trigger
Working Rest
2 sec
Dht22 State
dht22_read()
trigger_sensor()
Application 1
dht22_read()
trigger_sensor()
Application 2
? ?issue
dht22_read()
get_temp()
Application 1
dht22_read()
get_temp()
Application 2
timer_update(2 sec)
trigger_sensor()
update_temp()
Temp.
Value
Revised ProcessInitial Process

8.
2-1 Linux Driver for DHT22
/dev 存取介面 /sys 存取介面
邏輯分析儀驗證波形

9.
2-2 Linux Driver for HC-SR04
hc-sr04的通訊機制：
hcsr04_trigger() {
gpio_set_direction(pin, out);
gpio_set_value(pin, high);
udelay(10);
gpio_set_value(pin, low);
}
hcsr04_measure() {
interrup_setup;
hcsr04_trigger();
wait_event();
elapsed = endT – start;
}
hcsro4_irq_handler() {
if(gpio == high)
startT = get_time();
else {
endT =get_time();
send_event();
}
}
Interrup_setup() {
reuest_irq(pin,
hcsro4_irq_handler,
FALLING_And_RISING)
}
Elapsed
= (end_time – start_time) us
Sound_Speed
= 340 x 10-6 m/us
Distance
= Elapsed / 2 x Sound_Speed
Elapsed
1. interrup_setup 2. trigger
3. interrup_irq
4. process_data

10.
2-2 Linux Driver for HC-SR04
/sys 存取介面
邏輯分析儀驗證波形

11.
2-3 Linux Driver for GY-273
/dev/gy273
applicaiton
I2C-dev
gy273.dtbo
gy273@50{
compatible = “gy273“
reg = <0x1E>;
};
Device Tree Overlay
gy273.ko
I2C Client Driver (I2C-dev)
.driver = {
.name = “gy273”
}
.probe = gy273_probe,
.remove = gy273_remove,
gy273_probe = {
register_chardev();
cdev_init();
cdev_add();
}
當 device的compatible
等於driver的.name時
gy273_probe才會建立
字元裝置
1. add_device_node
2. add_i2c_dirve 3. probe
/dev/gy273

12.
2-3 Linux Driver for GY-273
/dev 存取介面
測試程式讀取 /dev/gy273

13.
IoT應用實例 #1
DHT22
風扇
溫溼度感測器應用
OLED

14.
IoT應用實例 #2
距離感測器 電子羅盤感測器
HC-SR04
GY-273
PIR

15.
IOT Platform
ThingsBoard

16.
Web呈現感測數值