[time-nuts] USB fun and games

[Hal Murray]

After all my noise about the FT232R polling at 125 microseconds, I thought I 
would see if I could make a hanging bridge.  To my surprise and annoyance, it 
was polling at 1ms.

I screwed around for a while but couldn't get it to work on the hardware and 
kernel that it was plugged into.

I think there is a magic mux between the USB hardware/firmware on the host and 
the wires to the connectors.  If I plug a thumb drive into a connector, I get 
a different USB hub than I get when I plug a GPS mouse into the same connector.

After a while, I tried it in a newer system.  That polls at 125 microseconds.  
Well, most of the time. Every 5 min (rough) it gets another 125 microseconds 
added to the timing.

Here are a couple of graphs.

http://users.megapathdsl.net/~hmurray/time-nuts/USB/USB-125usec-a.png
http://users.megapathdsl.net/~hmurray/time-nuts/USB/USB-125usec-b.png

Does anybody know anything about this quirk?

Initially, I had another GPS gizmo plugged into that box.  Now there there are 
no other USB devices.

Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 0403:6001 Future Technology Devices International, Ltd 
FT232 Serial (UART) IC
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub



-- 
These are my opinions.  I hate spam.