MaixII M2dock PWM 调试

PWM介绍

PWM（Pulse Width Modulation）控制——脉冲宽度调制技术，通过对一系列脉冲的宽度进行调制，来等效地获得所需要波形（含形状和幅值）.PWM控制技术在逆变电路中应用最广，应用的逆变电路绝大部分是PWM型，PWM控制技术正是有赖于在逆变电路中的应用，才确定了它在电力电子技术中的重要地位。V831的PWM功能是由硬件产生的,所以我们只用配置好硬件寄存器即可.芯片寄存器请参考V833／V831 Datasheet V1.0.pdf.

V831 Dock PWM 引脚

如下图所示,V831有8个引脚可以输出PWM波,但是由于复用关系,我们并不能随心所欲的使用这8个引脚.所以我们要注意他们的复用关系,以PH0为例,但是这个引脚被SPI功能所占用,所以我们使用时,需要改变PWM功能所在引脚的复用功能才能正常使用PWM功能.能够被我们正常使用的功能引脚是PH6、PH7 和 PH8引脚,其他引脚使用时需要注意引脚复用关系.如需一定要使用,请参考 改变引脚复用关系.

PWM LED 测试

使用 sysfs 操作 PWM 的例子：

#首先打开PWM6通道
cd /sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0

root@sipeed:/sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0# echo 6 > export 

root@sipeed:/sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0# ls
device     export     npwm       pwm6       subsystem  uevent     unexport

#设置PWM周期
cd /sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0/pwm6
root@sipeed:/sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0/pwm6# echo 1000000 > period 

#设置PWM占空比
root@sipeed:/sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0/pwm6# echo 10000 > duty_cycle

#开启PWM功能
root@sipeed:/sys/devices/platform/soc/300a000.pwm/pwm/pwmchip0/pwm6# echo 1 > enable

#用示波器或者LED灯观察PH0端口是否有PWM波输出

Python-PWM

import time
from maix import pwm
import signal


def handle_signal_z(signum,frame):
    print("APP OVER")
    exit(0)


signal.signal(signal.SIGINT,handle_signal_z)


with pwm.PWM(6) as pwm6:
        pwm6.period = 1000000
        pwm6.duty_cycle = 10000
        pwm6.enable = True
        duty_cycle = 10000
        while True:
            for i in range(1,10):
                pwm6.duty_cycle = 10000 * i
                time.sleep(1)

V831 Dock 改变引脚复用关系

以PH0为例,查询v831的datasheet手册我们能得到:


0x0300B0FC寄存器的最低三位是控制PH0的引脚复用关系的,我们通过linux指令进行查看该寄存器中的值.

root@sipeed:/sys/class/sunxi_dump# ls
compare  dump     rw_byte  write
root@sipeed:/sys/class/sunxi_dump# echo 0x0300B0FC > dump 
root@sipeed:/sys/class/sunxi_dump# cat dump 
0x77114444

由寄存器中的值我们知道最低两位是00,为此我们改变最低位的值,然后再写回去.

root@sipeed:/sys/class/sunxi_dump# echo 0x0300B0FC 0x77114442 > write 
root@sipeed:/sys/class/sunxi_dump# cat dump 
0x77114442

修改成功后,我们就可以正常使用PWM0通道的PWM波输出了.

#使用PWM0的python3模块,使用其他复用引脚可以参考该写法
#import PWM就可以使用
"""Linux PWM driver sysfs interface"""

import os
import struct
__author__ = 'Scott Ellis'
__version__ = '1.0'
__license__ = 'New BSD'
__copyright__ = 'Copyright (c) 2016 Scott Ellis'
from types import (
    TracebackType,
)
from typing import (
    Optional,
    Type,
)
class PWM(object):
    """
    A class to work with the Linux PWM driver sysfs interface
    """

    def __init__(self, channel: int = 0, chip: int = 0) -> None:
        """ Specify channel and chip when creating an instance
        The Linux kernel driver exports a sysfs interface like this
            /sys/class/pwm/pwmchip<chip>/pwm<channel>
        A <chip> can have multiple <channels>.
        The channel and chip are determined by the kernel driver.
        For example the two PWM timers from the RPi kernel driver
        show up like this
            /sys/class/pwm/pwmchip0/pwm0
            /sys/class/pwm/pwmchip0/pwm1
        To use the RPi timers create instances this way
            pwm0 = PWM(0) or PWM(0,0)
            pwm1 = PWM(1) or PWM(1,0)
        """
        self._channel = channel
        self._chip = chip
        self.base = '/sys/class/pwm/pwmchip{:d}'.format(self._chip)
        self.path = self.base + '/pwm{:d}'.format(self._channel)
        #调整引脚复用功能
        with open("/sys/class/sunxi_dump/dump","wb") as f:
            f.write(b'0x0300B0FC')
        with open("/sys/class/sunxi_dump/dump","rb") as f:
            self.gpio = f.read()
            self.gpio = self.gpio[:-1]
        with open("/sys/class/sunxi_dump/write","wb") as f:
            gpio_H0 = int(self.gpio,16)
            gpio_H0 &= ~0x00000007
            gpio_H0 |= 0x00000002
            gpio_io = b'0x0300B0FC ' + bytes(hex(gpio_H0), 'ascii')
            f.write(gpio_io)
        if not os.path.isdir(self.base):
            raise FileNotFoundError('Directory not found: ' + self.base)

    # enable class as a context manager
    def __enter__(self) -> 'PWM':
        self.export()
        return self

    def __exit__(self,
            exc_type: Optional[Type[BaseException]],
            exc_value: Optional[BaseException],
            traceback: Optional[TracebackType]) -> None:
        self.enable = False
        self.inversed = False
        self.unexport()
        #还原引脚复用功能
        with open("/sys/class/sunxi_dump/dump","wb") as f:
            f.write(b'0x0300B0FC')
        with open("/sys/class/sunxi_dump/dump","rb") as f:
            self.gpio_o = f.read()
            self.gpio_o = self.gpio[:-1]
        with open("/sys/class/sunxi_dump/write","wb") as f:
            gpio_H0 = int(self.gpio,16)
            gpio_H0 &= 0x00000007
            gpio_H0_o = int(self.gpio_o,16)
            gpio_H0_o &= ~0x00000007
            gpio_H0_o |= gpio_H0
            gpio_io = b'0x0300B0FC ' + bytes(hex(gpio_H0_o), 'ascii')
            f.write(gpio_io)
        return

    def export(self) -> None:
        """Export the channel for use through the sysfs interface.
        Required before first use.
        """
        if not os.path.isdir(self.path):
            with open(self.base + '/export', 'w') as f:
                f.write('{:d}'.format(self._channel))

    def unexport(self) -> None:
        """Unexport the channel.
        The sysfs interface is no longer usable until it is exported again.
        """
        if os.path.isdir(self.path):
            with open(self.base + '/unexport', 'w') as f:
                f.write('{:d}'.format(self._channel))

    @property
    def channel(self) -> int:
        """The channel used by this instance.
        Read-only, set in the constructor.
        """
        return self._channel

    @property
    def chip(self) -> int:
        """The chip used by this instance.
        Read-only, set in the constructor.
        """
        return self._chip

    @property
    def period(self) -> int:
        """The period of the pwm timer in nanoseconds."""
        with open(self.path + '/period', 'r') as f:
            value = f.readline().strip()

        return int(value)

    @period.setter
    def period(self, value: int) -> None:
        with open(self.path + '/period', 'w') as f:
            f.write('{:d}'.format(value))

    @property
    def duty_cycle(self) -> int:
        """The duty_cycle (the ON pulse) of the timer in nanoseconds."""
        with open(self.path + '/duty_cycle', 'r') as f:
            value = f.readline().strip()

        return int(value)

    @duty_cycle.setter
    def duty_cycle(self, value: int) -> None:
        with open(self.path + '/duty_cycle', 'w') as f:
            f.write('{:d}'.format(value))

    @property
    def enable(self) -> bool:
        """Enable or disable the timer, boolean"""
        with open(self.path + '/enable', 'r') as f:
            value = f.readline().strip()

        return True if value == '1' else False

    @enable.setter
    def enable(self, value: bool) -> None:
        with open(self.path + '/enable', 'w') as f:
            if value:
                f.write('1')
            else:
                f.write('0')

    @property
    def inversed(self) -> bool:
        """normal polarity or inversed, boolean"""
        with open(self.path + '/polarity', 'r') as f:
            value = f.readline().strip()

        return True if value == 'inversed' else False

    @inversed.setter
    def inversed(self, value: bool) -> None:
        with open(self.path + '/polarity', 'w') as f:
            if value:
                f.write('inversed')
            else:
                f.write('normal')