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Heavy cost between USB_HostCdcDataSend and its callback on TWR-K65 USB EHCI Host

Question asked by johne smith on Mar 20, 2017
Latest reply on Apr 5, 2017 by johne smith

Below is what I've done to measure the interval between USB_HostCdcDataSend and its callback on TWR-65 USB EHCI Host.
1. Connect the K65 USB EHCI Host with FTDI device.
2. Send data packet to device via USB_HostCdcDataSend and set the time as T1.
3. Once the callback comes, set the time as T2.
4. T2 - T1 is nearly 2ms. Moreover, if there happens to be an IN transfer between the USB_HostCdcDataSend and its callback, then the value of (T2 - T1) would be nearly 5ms.

That's totally too long a cost for real time systems. However, the FTDI device can response to the PC host within 1ms. I suspect it is an issue in USB low level driver. 

BTW, I didn't see any NAK after calling USB_HostCdcDataSend.


Can anyone help to verify this issue, or share some performance benchmark in this case?