Hi,
i need information about USB device’s throughput and latency allowed both during upward(from device) and downward(to the device) transfer. Can any one provide me some related information ?
I am interested for devices like printer, camera, memory stick, scanner, keyboard and mouse.
With thanks in advance,
barun
xxxxx@gmail.com wrote:
i need information about USB device’s throughput and latency allowed both during upward(from device) and downward(to the device) transfer. Can any one provide me some related information ?
I am interested for devices like printer, camera, memory stick, scanner, keyboard and mouse.
I would think Google would be a far better – and far more efficient –
resource for this type of information than this mailing list. The
highly readable USB 2.0 specification from www.usb.org also discusses
this topic in depth.
The type of device is irrelevant. The USB 2.0 bus is clocked at 480MHz,
which puts an upper limit at 60 MB/s. In fact, there are several types
of overhead that reduce the achievable bandwidth. We have been able to
sustain better than 45 MB/s on Windows using bulk pipes.
USB 2.0 transfers are all scheduled in units of microframes, which are
125us each. The host controller maps out the next microframe in
advance, and then triggers it when the time comes. So, in the best
case, you get results back within 125us. However, there are 4 different
types of pipes , and they each have different attributes. Isochronous
and interrupt pipes “reserve” a section of the overall bandwidth, so you
get guaranteeds on the bandwidth and latency, but their bandwidth is
limited A single isochronous pipe is limited to 24MB/s. Bulk pipes,
on the other hand, compete for whatever bandwidth is left unreserved,
but they can chew up as much as is available.
–
Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.