无法通过具有指定设备id的pylibftdi与FTDI设备通信

Question

我有一个USB设备，使用FTDI芯片，我可以在Linux中识别：

user@user:~/src/libftdi/build$ lsusb
Bus 009 Device 008: ID 0403:faf0 Future Technology Devices International, Ltd 

或：

user@user:~$ lsusb -v -d 0403:faf0

Bus 009 Device 008: ID 0403:faf0 Future Technology Devices International, Ltd 
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0         8
  idVendor           0x0403 Future Technology Devices International, Ltd
  idProduct          0xfaf0 
  bcdDevice            6.00
  iManufacturer           1 Thorlabs
  iProduct                2 APT DC Motor Controller
  iSerial                 3 83836244
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           32
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xc0
      Self Powered
    MaxPower                0mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass    255 Vendor Specific Subclass
      bInterfaceProtocol    255 Vendor Specific Protocol
      iInterface              2 APT DC Motor Controller
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
Device Status:     0x0001
  Self Powered

我已经安装了pylibftdi，并想出了如何列出它们

In [26]: dev.driver.list_devices()
Out[26]: 
[('Thorlabs', 'APT DC Motor Controller', '83836244'),
 ('Thorlabs', 'APT DC Motor Controller', '83838416'),
 ('Thorlabs', 'APT DC Motor Controller', '83837686'),
 ('Thorlabs', 'APT DC Motor Controller', '83836852'),
 ('Thorlabs', 'APT DC Motor Controller', '83837812'),
 ('Thorlabs', 'APT DC Motor Controller', '83825518'),
 ('Thorlabs', 'APT DC Motor Controller', '83838377'),
 ('Thorlabs', 'APT DC Motor Controller', '83838379'),
 ('Thorlabs', 'APT DC Motor Controller', '83836769'),
 ('Thorlabs', 'APT DC Motor Controller', '83837688'),
 ('Thorlabs', 'APT DC Motor Controller', '83836926'),
 ('Thorlabs', 'APT DC Motor Controller', '83837767'),
 ('Thorlabs', 'APT DC Motor Controller', '83836887'),
 ('Thorlabs', 'APT DC Motor Controller', '83836737'),
 ('Thorlabs', 'APT DC Motor Controller', '83838436'),
 ('Thorlabs', 'APT DC Motor Controller', '83837639'),
 ('Thorlabs', 'APT DC Motor Controller', '83836040'),
 ('Thorlabs', 'APT DC Motor Controller', '83837769'),
 ('Thorlabs', 'Brushed Motor Controller', '27251492'),
 ('Thorlabs', 'Brushed Motor Controller', '27251539')]


In [1]: from pylibftdi import USB_PID_LIST, USB_VID_LIST, Device
In [2]: USB_PID_LIST.append(0xFAF0)
In [3]: dev = Device()
In [4]: dev.driver.libftdi_version()
Out[4]: libftdi_version(major=0, minor=0, micro=0, version_str='< 1.0 - no ftdi_get_library_version()', snapshot_str='unknown')

pylibusb的文档中说，属性device\u id可用于指定我尝试连接到的设备：

 |  __init__(self, device_id=None, mode='b', encoding='latin1', interface_select=None, device_index=0, **kwargs)
 |      Device([device_id[, mode, [OPTIONS ...]]) -> Device instance
 |      
 |      represents a single FTDI device accessible via the libftdi driver.
 |      Supports a basic file-like interface (open/close/read/write, context
 |      manager support).
:param device_id: an optional serial number of the device to open.
 |          if omitted, this refers to the first device found, which is
 |          convenient if only one device is attached, but otherwise
 |          fairly useless.

下面是我的简单代码，其中我创建了两个实例dev1和dev2。对于dev2，我没有指定设备id（因此没有特定的序列号），对于dev1，我指定。我可以成功地与dev2通信，但无法与dev1通信：

>>>from pylibftdi import USB_PID_LIST, USB_VID_LIST, Device
>>>from struct import pack, unpack

>>>USB_PID_LIST.append(0xFAF0)

>>>command = pack('BBBBBB',0x05,0x00,0x00,0x00,0x50,0x01)

>>>dev2 = Device();
>>>dev2.baudrate = 115200;
>>>dev2.writelines(command);
>>>dev2.readline()
 '\x06\x00T\x00\x81P\xc0z\xf2\x04TDC001\x00\x00\x10\x00\x03\x00\x02\x00TDC001 DC Servo Drive\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00104927Apr\x00\x01\x00\x02\x00\x00\x00\x01\x00'

>>>dev1 = Device(device_id = '83838416');
>>>dev1.baudrate = 115200;
>>>dev1.writelines(command);
>>>dev1.readline()
''

因为，我有几十个这样的USB设备连接到一台计算机上，这是我必须能够创建一个实例，并与一个定义了序列号的设备交谈。你知道吗

我不确定这是一个错误还是我做错了什么。你知道吗

稍后添加：

不知何故，这是历史的依赖。如果在重新启动python之后运行相同的代码，则会得到一个空字符串作为响应。我不知道我现在做的和以前有什么不同。你知道吗

In [1]: from pylibftdi import USB_PID_LIST, USB_VID_LIST, Device

In [2]: from struct import pack, unpack

In [3]: USB_PID_LIST.append(0xFAF0)

In [4]: command = pack('BBBBBB',0x05,0x00,0x00,0x00,0x50,0x01)

In [5]: dev2 = Device();dev2.baudrate = 115200;dev2.writelines(command);dev2.readline();

In [6]: dev2.__dict__
Out[6]: 
{'_baudrate': 115200,
 '_opened': True,
 'ctx': <ctypes.c_char_Array_1024 at 0x7ff2008a1b00>,
 'decoder': <encodings.latin_1.IncrementalDecoder at 0x7ff2006906d0>,
 'device_id': None,
 'device_index': 0,
 'driver': <pylibftdi.driver.Driver at 0x7ff200690610>,
 'encoder': <encodings.latin_1.IncrementalEncoder at 0x7ff200681f90>,
 'encoding': 'latin1',
 'fdll': <CDLL 'libftdi.so.1', handle 5627c1668650 at 7ff2011d08d0>,
 'interface_select': None,
 'mode': 'b'}

In [8]: 

Answer 1

你只对uart（类似）模式感兴趣吗？如果是这样的话，你可以看看pyserial。尤其是serial.tools.list\u端口.comports（）函数：

import serial
import serial.tools.list_ports

print([(x.device,x.hwid,x.description,x.location,x.serial_number) for x in serial.tools.list_ports.comports()])

这样您就可以获得正确的描述，然后通过打开端口

ports = [x.device for x in serial.tools.list_ports.comports() if search_string in x.hwid]
serial.Serial(ports[0], 115200)