Bus Interval Adjustment Message (BIAM) in USB 3.0

[ChongHan]

Hi

In USB 3.0, there is a device notification function - Bus Interval Adjustment Message (BIAM), which used to adjust bus interval for synchronization with host's clock by an external clock.

Bus interval is 125us and can be adjusted up to +/- 13.3333us.
Besides, for one BusIntervalAdjustmentGranularity unit, requires the host to adjust bus interval timer by one 60Mhz click period (8 HS bit times) every 4096 bus intervals.

Here, i am confusing about the unit and time used for adjust bus interval. When the device sent request to host to adjust the bus interval by increasing 1 BusIntervalAdjustmentGranularity unit, so how much the bus interval will will adjust? So only every 4096 bus interval able to be adjust? Or every bus interval in 4096 bus interval can be adjust? IF two or more unit (not more than 4096) request to increase, so how it works? Is that increase each 4096 bus interval? 2 unit mean 2 bus interval to adjust?

Sorry for my bad English, i hope all of you can share some knowledges or experiences with me and others. Thanks in advance.

[Barry Twycross]

I'm not sure what your question is, but my advice would be to not use the message. In the 3.1 spec (sec 8.5.6.6), it says "Note that this notification will be deprecated in a future release." So they're encouraging you not to use the message.

I've never used the message myself, and I was surprised to see it in the spec. There was a similar mechanism in the USB 1.0 spec, it was never used and got taken out of the 2.0 spec. Now someone put it back in the 3.0 spec and they're going to take it out again.