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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