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[jaypdx]

We're using an FT2232HQ to interface with an I2C peripheral.  We're basically writing two bytes and then reading back four bytes over and over.  We're seeing a delay of between 1-2ms between each transfer (this is once we change the latency timer to 2).  Is there any way to reduce this dead time?  Is it limited by the USB 'polling interval'?  I understand the polling interval is 1ms for full-speed and 125us for high-speed USB.  Does the FT2232HQ support high-speed USB operation for I2C?

[FTDI Community]

Hi,

You can try setting the latency timer to 1ms. This will make the device ran as fast as it can.

Best Regards
FTDI Community

[jaypdx]

Yes I've done this and it is a little faster than set_latency_timer(2).  But doesn't this device support high-speed USB (480Mbits/s)?  Or does it only run at full-speed (12Mbps) for I2C transfers?

[FTDI Community]

Hi,

yes, FT2232H is a high-speed device. The driver can only operate with 1ms latency minimum.

Best regards
FTDI Community