Question

我正在做一个小项目，通过 USB 从三丰数字指示器读取值。通过采用 libUSB，我可以打开具有正确 PID 和 VID 的设备，并获得以下信息：

Reading device descriptor:
            length: 18
      device class: 0
               S/N: 3
           VID:PID: 0FE7:4001
         bcdDevice: 1100
   iMan:iProd:iSer: 1:2:3
          nb confs: 1

Reading BOS descriptor: no descriptor

Reading first configuration descriptor:
             nb interfaces: 1
              interface[0]: id = 0
interface[0].altsetting[0]: num endpoints = 1
   Class.SubClass.Protocol: 03.00.00
       endpoint[0].address: 81
           max packet size: 0008
          polling interval: 0A

Reading string descriptors:
   String (0x01): "Mitutoyo"
   String (0x02): "USB-ITN"
   String (0x03): "60026369"

然后，我尝试了以下代码

int transferred = 0; // actual size for write
int received = 0; // actual size for read
const int TRANSFER_SIZE = 9;  // transfer size
unsigned char buffer[TRANSFER_SIZE]; // USB buffer

char _cmd[TRANSFER_SIZE]; // command to be sent to device
strncpy_s(_cmd, "\0", sizeof("\0"));
strncat_s(_cmd, "R\r", sizeof("R\r"));
printf("_cmd %s \n", _cmd);

const int command_len = strlen(_cmd); // Get the length of the command string we are sending
if (command_len > TRANSFER_SIZE)
{
    printf("Error: command is larger than our limit of %i\n", TRANSFER_SIZE);
    return -1;
}

memset(buffer, 0, TRANSFER_SIZE); // Zero out buffer to pad with null values 
memcpy(&buffer, _cmd, strlen(_cmd)); // put command into buffer

// write to device
int e = libusb_bulk_transfer(handle, 0, buffer, TRANSFER_SIZE, &transferred, 1500);
if (e >= 0)
{
    printf("\nWrite successful!");
    printf("\nSent %d bytes with string: %s\n", transferred, buffer);
}
else
    printf("\nError in write! e = %d and transferred = %d\n", e, transferred);

// read from device
e = libusb_bulk_transfer(handle, BULK_EP_IN, buffer, TRANSFER_SIZE, &received, 1000);
if (e >= 0)
{
    printf("\nReceived: ");
    printf("%c", buffer[i]); //Will read a string from LPC2148
}
else
    printf("\nError in read! e = %d and received = %d\n", e, received);

但是，我得到了

Error in write! e = -1 and transferred = 0
Error in read! e = -1 and received = 0

对应于libusb_error_io。我没有找到有关错误类型的任何详细信息。所以我想知道错误是否表明 I/O 地址错误，或者我发送到设备的协议错误，或者缺少 libUSB 的某些系统依赖项？

顺便说一句，我随机尝试了设备的协议，因为我没有找到任何这种类型的文档。命令 "R\r" 来自 Mitutoyo 的不同类型的设备。如果有人碰巧知道 Mitutoyo 数字指示器系列 ID-S 的协议，如果能提供更多信息，我将不胜感激。

另一个问题，是否有必要在缓冲区的开头放一个"\0"？如果低速设备的标准传输大小是 8，那么我应该发送到设备的缓冲区是 8+1。对吗？

谢谢。

使用 libusb_bulk_transfer 从 USB HID 设备读取，并获取 libusb_error_io

0 个答案: