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Gadget应用实例之zero

实例应用 Zero
2023-09-14 09:16:19 时间

Gadget应用实例之zero

一、编写程序

1.1 编程思路

涉及的程序如下图所示：

在这里插入图片描述

基于libusb编写程序：

  • 找到设备
  • 选择配置：loopback、sourcesink
  • 得到端点：找到interface进而得到endpoint
  • 读写数据：操作endpoint

1.2 zero设备的描述符

在Ubuntu里执行如下命令：

$ lsusb -v -d 0525:a4a0

可以列出zero设备的描述符：

Bus 001 Device 002: ID 0525:a4a0 Netchip Technology, Inc. Linux-USB "Gadget Zero"
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          255 Vendor Specific Class
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x0525 Netchip Technology, Inc.
  idProduct          0xa4a0 Linux-USB "Gadget Zero"
  bcdDevice            4.09
  iManufacturer           1
  iProduct                2
  iSerial                 3
  bNumConfigurations      2
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           69
    bNumInterfaces          1
    bConfigurationValue     3
    iConfiguration          4
    bmAttributes         0xc0
      Self Powered
    MaxPower                2mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0
      bInterfaceProtocol      0
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       1
      bNumEndpoints           4
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0
      bInterfaceProtocol      0
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0400  1x 1024 bytes
        bInterval               4
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0400  1x 1024 bytes
        bInterval               4
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           32
    bNumInterfaces          1
    bConfigurationValue     2
    iConfiguration          5
    bmAttributes         0xc0
      Self Powered
    MaxPower                2mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0
      bInterfaceProtocol      0
      iInterface              6
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0

它有2个配置：

  • 第1个配置(bConfigurationValue = 2)对应loopback功能：里面有1个接口，接口有1个setting，下面有2个endpoint
  • 第2个配置(bConfigurationValue = 3)对应SourceSink功能：里面有1个接口，接口有2个setting
    • 第1个setting下面有2个endpoint：都是bulk端点
    • 第2个setting下面有4个endpoint：2个是bulk端点，另外2个是Isochronous端点

1.3 编程

参考libusb示例：libusb\examples\xusb.c

二、上机实验

实验步骤：

  • 先安装g_zero驱动程序：在开发板上执行modprobe g_zero

  • 然后连接OTG线到PC

  • 在Ubuntu中识别出设备

  • 执行测试程序

    • 先编译：在Ubuntu里执行如下命令

      apt-cache search libusb  # 查找libusb开发包
sudo apt install libusb-1.0-0-dev  # 安装libusb开发包
gcc -o zero_app zero_app.c -lusb-1.0  # 编译

    • 测试：在Ubuntu里执行如下命令

      $ sudo ./zero_app -l    # 列出设备的配置值
config 0: bConfigurationValue = 3
config 1: bConfigurationValue = 2


# 测试loopback功能
$ sudo ./zero_app -s 2                  # 选择loopback的配置
$ sudo ./zero_app -wstr www.100ask.net  # 写入字符串
current config: 2
in_ep = 0x81, out_ep = 0x1
$ sudo ./zero_app -rstr                # 读出字符串
current config: 2
in_ep = 0x81, out_ep = 0x1
Read string: www.100ask.net

$ sudo ./zero_app -w 1 2 3 4 5 6 7 8   # 写入8个字节
current config: 2
in_ep = 0x81, out_ep = 0x1
sudo ./zero_app -r                     # 读到8个字节
current config: 2
in_ep = 0x81, out_ep = 0x1
transferred != in_ep_maxlen
Read datas:
01 02 03 04 05 06 07 08


    #测试Source/Sink功能
    $ sudo ./zero_app -s 3                   # 选择source/sink的配置         
    original@ubuntu:~/work/libusb_zero$ sudo ./zero_app -r  # 读数据
    current config: 3
    in_ep = 0x81, out_ep = 0x1
    Read datas:
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    

    sudo ./zero_app -w 0 0 0  # 写数据, 只能写入0, 
                              # 写入其他值将会导致开发板上的驱动认为是错误然后halt out端点
                              # 然后只能重新执行 ”sudo ./zero_app -s 3“ 才能恢复

致谢

以上笔记源自韦东山老师的视频课程，感谢韦老师,韦老师是嵌入式培训界一股清流，为嵌入式linux开发点起的星星之火，也愿韦老师桃李满园。聚是一团火，散是满天星！

在这样一个速食的时代，坚持做自己，慢下来，潜心琢磨，心怀敬畏，领悟知识，才能向下扎到根，向上捅破天，背着世界往前行！
仅此向嵌入行业里的每一个认真做技术的从业者致敬！

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