ezPWMForRaspberry

本模块使用了node-rpio, 所以，请配置以下环境。

由于使用pwm，需要sudo权限。 或者把pi用户放入gpio用户组。

$3

If running a newer Raspbian release, you will need to add the following line to
/boot/config.txt and reboot:

``
dtoverlay=gpio-no-irq
`

Without this you may see crashes with newer kernels when trying to poll for pin
changes.

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By default the module will use /dev/gpiomem when using simple GPIO access.
To access this device, your user will need to be a member of the gpio group,
and you may need to configure udev with the following rule (as root):

`shell
$ cat >/etc/udev/rules.d/20-gpiomem.rules <SUBSYSTEM=="bcm2835-gpiomem", KERNEL=="gpiomem", GROUP="gpio", MODE="0660"
EOF
`

For access to i²c, PWM, and SPI, or if you are running an older kernel which
does not have the bcm2835-gpiomem module, you will need to run your programs
as root for access to /dev/mem.

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`
npm i ezpwmforraspberry --save
`

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`javascript
const ezPWM = require('ezpwmforraspberry');

const pwm = new ezPWM();

`

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#### 1.百分比方式(精度100， 从0~100)

`javascript
// 打开PWM
pwm.openPWMByPercent(ezPWM.PWMPin.PIN12);

// 更新占空比
pwm.updatePWMByPercent(ezPWM.PWMPin.PIN12,0);

// 从0到100
for (let index = 0; index < 100; index++) {
rpio.sleep(0.1);
console.log('updatePWMByPercent', ezPWM.PWMPin.PIN12 ,index);
pwm.updatePWMByPercent(ezPWM.PWMPin.PIN12,index);
}

`

#### 2.高精度方式

`javascript
// 打开PWM
pwm.openPWM(ezPWM.PWMPin.PIN12, 0, total=1024);

// 更新占空比
pwm.updatePWM(ezPWM.PWMPin.PIN12, 0)

// 从0到100
for (let index = 0; index < 1024; index++) {
rpio.sleep(0.1);
console.log('updatePWMByPercent', ezPWM.PWMPin.PIN12 ,index);
pwm.updatePWMByPercent(ezPWM.PWMPin.PIN12,index);
}
`

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树莓派4B之前的版本，时钟频率是19.2MHz, 4B的时钟频率是54MHz。

#### 给PWM口分配频率

通过divosor来设置PWM口的时钟频率的,

`javascript
const pwm = new ezPWM('physical', 2048);
`

如上，设置了2048， 则divosor=54e6/2048，约2.6367MHz频率。

设置了时钟频率后，再设置精度, 也可称为分辨率。 假设我们设置精度为1024

那么，2.6367Mhz/1024 ~= 25Hz, 也就是每秒25个1024分辨率的PWM信号。

设置占空比

`javascript
pwm.openPWM(ezPWM.PWMPin.PIN12, low=0, total=1024);

pwm.updatePWM(ezPWM.PWMPin.PIN12, low=800);
``

参考博文:

https://raspberrypi.stackexchange.com/questions/4906/control-hardware-pwm-frequency/9725#9725

https://github.com/jperkin/node-rpio/issues/2