Re: [Libusb-devel] packet read

[Tim R. <ti...@pr...>]

Szasz Pal wrote:

>Is it possible to read data in packet mode?
>Ie. right now if I read using bulk_read, it reads the required amount of 
>  data, which might be split in several packets. But I want to limit the 
>read to 1 packet only. Is it possible somehow? (The reason is the device 
>adds two bytes at the beginning of each packet. So if the data I should 
>get is "MESSAGE", I might got 1 packet:
>
>0x11 0x22 "MESSAGE"
>
>but I might got 2 packets:
>0x11 0x22 "MESS"
>0x11 0x22 "AGE"
>
>And if I read using bulkread, i will read
>0x11 0x22 "MESSAGE"
>in the first casem and in the second case:
>0x11 0x22 "MESS" 0x11 0x22 "AGE"
>

When you say "packet", do you really mean "USB packet"?  It's up to you
to know how large each packet is.  If your pipe is configured for
64-byte packets, then just do the reads 64 bytes at a time.

If your device really sends back variable-length USB packets, then you
may have to scan for the cookie yourself.  You may be able to set a
short timeout and handle one packet at a time, but your performance is
going to be very poor.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.