D21 / USB HID latency

[rubear]

HI,

I am communicating with the D21 via USB. I used the ASF Wizard hid_generic driver.
My Windows C# app sends a packet, the D21 sends an ack. The ack is delayed by 8ms. How can I shorten this?
I've look everywhere and cannot find the source of this delay.

Update:
I tried sending 64 byte USB packets with out a software layer ack, just using the underlying HID protocol for flow control.
The time to write a 64 byte packet is about 3 ms. Has anyone tested Atmel's HID solution and have any ideas?

Thanks,
-Robert