【EmbeddedDev】BBB上打开PWM串口并进行操作

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1.参考链接

http://www.lai18.com/content/8359588.html
https://briancode.wordpress.com/2015/01/06/working-with-pwm-on-a-beaglebone-black/

2. 串口PIN脚对应表

EXPORT NUMBERPIN NAMEPINS 0 EHRPWM0A P9.22,P9.31 1 EHRPWM0B P9.21,P9.29 2 ECAPPWM0 P9.42 3 EHRPWM1A P9.14,P8.36 4 EHRPWM1B P9.16,P8.34 5 EHRPWM2A P8.19,P8.45 6 EHRPWM2B P8.13,P8.46 7 ECAPPWM2 P9.28

3.加载PWM设备驱动

首先加载am33xx_pwm，各个pwm串口都会需要依赖它。
通过cat slots可以查看已加载的结果列表，其中P-O-L表示已加载并且启用。

root@beaglebone:/sys/class/pwm# cd /sys/devices/bone_capemgr.9root@beaglebone:/sys/devices/bone_capemgr.9# echo am33xx_pwm > slotsroot@beaglebone:/sys/devices/bone_capemgr.9# cat slots 0: 54:PF---  1: 55:PF---  2: 56:PF---  3: 57:PF---  4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G 5: ff:P-O-- Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI 6: ff:P-O-- Bone-Black-HDMIN,00A0,Texas Instrument,BB-BONELT-HDMIN 7: ff:P-O-L Override Board Name,00A0,Override Manuf,am33xx_pwm

然后加载指定pwm设备模块。

root@beaglebone:/sys/devices/bone_capemgr.9# cd /sys/class/pwmroot@beaglebone:/sys/class/pwm# echo 6 > exportroot@beaglebone:/sys/class/pwm# lsexport  pwm6  pwmchip0  pwmchip2  pwmchip3  pwmchip5  pwmchip7  unexport

最后加载指定端口P8_13的pwm驱动。

root@beaglebone:/sys/class/pwm# cd /sys/devices/bone_capemgr.9root@beaglebone:/sys/devices/bone_capemgr.9# echo bone_pwm_P8_13 > slotsroot@beaglebone:/sys/devices/bone_capemgr.9# cd /sys/class/pwmroot@beaglebone:/sys/class/pwm# lsexport  pwm6  pwmchip0  pwmchip2  pwmchip3  pwmchip5  pwmchip7  unexportroot@beaglebone:/sys/class/pwm# cd pwm6root@beaglebone:/sys/class/pwm/pwm6# lsdevice  duty_ns  period_ns  polarity  power  run  subsystem  uevent

4. 通过shell操作PWM

修改period_ns与duty_ns可以改变输出电压, 从而达到控制外设的效果。
值得注意的是, 如果连接了pwm的外设使用了独立电源的话，也需要把BBB的GND地线接口与独立电源的地线连接起来；否则因为回路不通而导致PWM控制失效。
另外，在每次修改两个值之前把run值置为0，修改完成后再置为1，表示打开状态。

root@beaglebone:/sys/class/pwm/pwm6# echo 0 > runroot@beaglebone:/sys/class/pwm/pwm6# echo 1000000 > period_nsroot@beaglebone:/sys/class/pwm/pwm6# echo 990000 > duty_nsroot@beaglebone:/sys/class/pwm/pwm6# echo 1 > runroot@beaglebone:/sys/class/pwm/pwm6# echo 0 > runroot@beaglebone:/sys/class/pwm/pwm6# echo 1000000 > period_nsroot@beaglebone:/sys/class/pwm/pwm6# echo 100000 > duty_nsroot@beaglebone:/sys/class/pwm/pwm6# echo 1 > run

5. 通过python操作RGB led灯

连线图(分别使用了P8_13, P8_19, P9_14作为rgb的控制串口, P8_2作为地线回路串口)
python代码示例

import Adafruit_BBIO.PWM as PWMimport timeimport randomred = "P8_13"green = "P8_19"blue = "P9_14"PWM.start(red, 100)PWM.start(blue, 100)PWM.start(green, 100)if __name__ == "__main__":        for i in range(0, 10000):                PWM.set_duty_cycle(red, random.randint(0, 100))                PWM.set_duty_cycle(green, random.randint(0, 100))                PWM.set_duty_cycle(blue, random.randint(0, 100))                time.sleep(0.5)

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