2.6.5 on openSuse 11.3
Changing it to
delta = (endtime - starttime).seconds - 0.0145
fixes the problem.
Congrats for PyFPGAMiner, it is really nice

ATM my Atlys with 50Mhz and depth:=2 is giving 3.2MH/s and I'm curious what performance I can reach.
I was thinking about using BlockRAM instead of Slice-FFs to squeeze in more logic and maybe ease the congestion problems of spartan 6 fpgas. A first glimpse showed that ISE is complaining about asynchronous reads in the current hw version.
I think it should help a lot to move all pipeline registers to BRAMS.