I am eagerly awaiting my first U2. These responses will be of great assistance when I throw it in with my U1's and Bfgminer running on a Raspberry Pi system. I had all the same problems trying to get my U1's to work. Two things made a huge difference.
1. Purchased a large 5vdc switching power supply to run my USB hubs... allowing almost 1 amp capacity for each miner.
2. copied the following statements in the following order to my bfg commandline:
--set-device antminer:clock=x0781 --icarus-options 115200:2:2 --icarus-timing long -S all
The icarus timing long statement causes the clock and hashrate to continually correct itself and is not appropriate in computer systems with a cpu load shared with other applications. You could experiment with "--icarus-timing short" which requires full CPU time without delays, and makes the self-corrections, but only for a limited time (~1 hr). Observing this, I saw my hash rate jump all over the place but over the course of a couple days it smoothed out until now after a couple weeks of continuous running, I see 3.16 or 3.17 gh/s on each miner with total errors at 0% and total rejected at .08% Very pleasing.
I had my main system blow it's power supply so now I've got a dual Coppermine main board handling the connection. In this case, the onboard USB can handle 1 ANT and 1 Erupter, from the outside, I have a 7 port hub ( bought the wrong kind, they are sideways ) and can only have it set as ant, erupter, ant, erupter and between the 2 closest to the power connection a D-Link USB extender ( 4 inch long USB male to female, now I know WHY they made these! ). I cut and soldered an old D-Link wireless's power adapter to get the hub
[email protected] and it will do strange things when I don't have 1 ANT per hub IC including sudden and mysterious hashing issues on either the ANT or Erupters. I've yet to use the --icarus-options as all 4 Erupterschug away around the rated 333 khash/sec and I can only go for =x0981 due to not adding the 10K SMD 0603 resistor ( yet ). With what I've got mining, I know I'm going to have to get a new hub ( with proper orientation ) and another used wireless with adapter if/when I get more Ants!
Power issues show up as the weirdest errors and easier to troubble shoot if you can find what part of the hub it's plugged in to.