Python(基于Pyusb)与C#(基于LibUsbDotNet)USB通信速度对比

1、实验背景

项目需求：下位机ZYNQ，需设计上位机与其通信，通信协议USB2.0。ZYNQ端固定Buffer长度为16k，即上位机向ZYNQ发送任意数据，ZYNQ每次反馈16k长度buffer。现对Python(基于Pyusb)与C#(基于LibUsbDotNet)的USB通信速度进行实验，实验结果见文章末尾

2、Bus Hound

Bus Hound超级软件总线协议分析器，在本实验中用于捕捉USB输入输出的协议包，以确保上位机与下位机通信正常

3、C# USB读写

C#使用LibUsbDotNet(LibUsbDotNet是一个.NET C#的USB库，适用于WinUsb,libusb-win32,Linux libusb v1.x)实现USB读写，如图所示：

具体代码如下：

using System;
using System.Text;
using System.Text.RegularExpressions;
using LibUsbDotNet;
using LibUsbDotNet.Main;

namespace Examples
{
    internal class ReadWrite
    {
        public static UsbDevice MyUsbDevice;

        #region SET YOUR USB Vendor and Product ID!

        public static UsbDeviceFinder MyUsbFinder = new UsbDeviceFinder(0x04b4, 0x00f0);

        #endregion

        public static void Main(string[] args)
        {
            ErrorCode ec = ErrorCode.None;

            try
            {
                // Find and open the usb device.
                MyUsbDevice = UsbDevice.OpenUsbDevice(MyUsbFinder);

                // If the device is open and ready
                if (MyUsbDevice == null) throw new Exception("Device Not Found.");

                // If this is a "whole" usb device (libusb-win32, linux libusb)
                // it will have an IUsbDevice interface. If not (WinUSB) the 
                // variable will be null indicating this is an interface of a 
                // device.
                IUsbDevice wholeUsbDevice = MyUsbDevice as IUsbDevice;
                if (!ReferenceEquals(wholeUsbDevice, null))
                {
                    // This is a "whole" USB device. Before it can be used, 
                    // the desired configuration and interface must be selected.

                    // Select config #1
                    wholeUsbDevice.SetConfiguration(1);

                    // Claim interface #0.
                    wholeUsbDevice.ClaimInterface(0);
                }

                // open read endpoint 1.
                UsbEndpointReader reader = MyUsbDevice.OpenEndpointReader(ReadEndpointID.Ep01);

                // open write endpoint 1.
                UsbEndpointWriter writer = MyUsbDevice.OpenEndpointWriter(WriteEndpointID.Ep01);

                // Remove the exepath/startup filename text from the begining of the CommandLine.
                string cmdLine = Regex.Replace(
                    Environment.CommandLine, "^\".+?\"^.*? |^.*? ", "", RegexOptions.Singleline);

                if (!String.IsNullOrEmpty(cmdLine))
                {
                    int bytesWritten;
                    ec = writer.Write(Encoding.Default.GetBytes(cmdLine), 2000, out bytesWritten);
                    if (ec != ErrorCode.None) throw new Exception(UsbDevice.LastErrorString);

                    byte[] readBuffer = new byte[16384];
                    while (ec == ErrorCode.None)
                    {
                        int bytesRead=4096;

                        // If the device hasn't sent data in the last 100 milliseconds,
                        // a timeout error (ec = IoTimedOut) will occur. 
                        for(int i=0; i<2500;i++)
                        {
                            ec = reader.Read(readBuffer, 100, out bytesRead);
                        }


                        if (bytesRead == 0) throw new Exception("No more bytes!");

                        // Write that output to the console.
                        Console.Write(Encoding.Default.GetString(readBuffer, 0, bytesRead));
                    }

                    Console.WriteLine("\r\nDone!\r\n");
                }
                else
                    throw new Exception("Nothing to do.");
            }
            catch (Exception ex)
            {
                Console.WriteLine();
                Console.WriteLine((ec != ErrorCode.None ? ec + ":" : String.Empty) + ex.Message);
            }
            finally
            {
                if (MyUsbDevice != null)
                {
                    if (MyUsbDevice.IsOpen)
                    {
                        // If this is a "whole" usb device (libusb-win32, linux libusb-1.0)
                        // it exposes an IUsbDevice interface. If not (WinUSB) the 
                        // 'wholeUsbDevice' variable will be null indicating this is 
                        // an interface of a device; it does not require or support 
                        // configuration and interface selection.
                        IUsbDevice wholeUsbDevice = MyUsbDevice as IUsbDevice;
                        if (!ReferenceEquals(wholeUsbDevice, null))
                        {
                            // Release interface #0.
                            wholeUsbDevice.ReleaseInterface(0);
                        }

                        MyUsbDevice.Close();
                    }
                    MyUsbDevice = null;

                    // Free usb resources
                    UsbDevice.Exit();

                }

                // Wait for user input..
                Console.ReadKey();
            }
        }
    }
}

注意此代码 byte[] readBuffer = new byte[16384]，readBuffer的大小决定reader.Read(readBuffer, 100, out bytesRead)中bytesRead大小，故此大小要根据实验进行调整。 int bytesRead=4096，该值不为0即可，如果至小于byte[] readBuffer = new byte[16384]中readBuffer的大小，其不直接影响reader.Read(readBuffer, 100, out bytesRead)中bytesRead大小

4、Python USB读写

Python使用Pyusb实现USB读写，如图所示：

详细代码如下：

import usb.core
import time

def find_usb_dev():
    all_devs = usb.core.find(find_all = True)
    for dev in all_devs:
         print(dev)

def usb_dev_enabled(dev):
    while(True):
        try:
            dev.set_configuration()
            break
        except Exception as e:
            print(e)

def usb_dev_write_bulk_out_ep(dev, endpoint, data, timeout):
    while(True):  
        try:
            data = dev.write(endpoint, data, timeout)
            break
        except Exception as e:
            print(e)
    return data
	
def usb_dev_read_bulk_in_ep(dev, endpoint, buffer_len, timeout):
    while(True):  
        try:
            data = dev.read(endpoint, buffer_len, timeout)
            break
        except Exception as e:
            print(e)
    return data


def read_dev():
    dev =  usb.core.find(idVendor= 0x04b4, idProduct= 0x00f0)
    # print(dev)
    data1 = bytes.fromhex('7e 7e')
    send1 = usb_dev_write_bulk_out_ep(dev, 0x1, data1, 2000)
    time_start = time.time()
    for i in range(10000):
        rev1 = usb_dev_read_bulk_in_ep(dev, 0x81,4096, 100)
    time_end = time.time()
    print(time_end - time_start)

if __name__ == "__main__":

    #### 普通
    read_dev()

5、USB通信速度

最终实验结果如下表，综合来看Python(基于Pyusb)与C#(基于LibUsbDotNet)的USB通信速度大体相同，但是Python的循环效率远低于C#，导致read次数多时，read时间大

上位机read次数	read buffer长度	C#所需时间(s)	Python所需时间(s)
80000	512	2.587	5.047
40000	1024	2.692	3.038
10000	4096	2.504	2.506
20000	4096	5.004	5.001
10000	8192	5.102	5.001
2500	16384	2.615	2.569
10000	16384	10.837	10.295

希望本文对大家有帮助，上文若有不妥之处，欢迎指正

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