Re: [Libusb-devel] strange problem,can anybody help me?

[Johannes E. <joh...@er...>]

On Sun, May 04, 2003, dw0811 <dw...@cn...> wrote:
> I have met a strange problem in my program.
> I have two hosts which run redhat7.3(2.4.18-3),and their usb hub was connected by a usbtousb bridge device(or PL2301),here is parts of my code:
> 
> 
>   char   recvbuf[4096];
>   char   sendbuf[4096];
> 
>         
>   int  j,sendlen;  
> 
>   strcpy(sendbuf,"STARTING");
> 
>   sendlen=4096;
> 
>   if (!strcmp(argv[1],"send"))
>   {
>    j=usb_bulk_write(udev,outendpoint,(char *)sendbuf,sendlen,5000);
>    if (j>0) 
>     printf("send %d\n",sendlen);
>    else
>       perror("Error");
>   }
> 
>   if (!strcmp(argv[1],"recv"))
>   {
>    for(;;)
>    {
>     j=usb_bulk_read(udev,inendpoint,(char *)recvbuf, sendlen,5000); 
>     if (j>0)
>     {
>        printf("recv %d\n",j);
>        printf("%s\n",recvbuf);
>        break;
>     }
>     else
>        perror("Error");  
>    }
>  }
> 
> i want run my test program on host A to send data,and another on host B to recv data,
> BUT,the data was recved by host B was unexpected,
> the data is not "STARTING",'\0' <repeats 4088 times>
> but '\0' <repeats 192 times>, "STARTING", '\0' <repeats 3896 times>
> 
> Sorry,my english is poor,i hope people here can understand me what i want to say, Thanks for your help.

I'm not too familiar with pl2301 (only the netchip 1080), but it could
be a FIFO which is causing this shifting of data. 192 bytes is a
multiple of the USB packet size, so I suspect it's just something the
pl2301 does that you may have to take into consideration.

JE