I've now started looking at the code in the DE2_115_makomk_mod branch, but I've hit a problem. The code compiles fine at CONFIG_LOOP_LOG2=2, 3 and 4 but its producing the wrong hashes (I'm just running at 40MHz for testing, not full blast) ... the mine.tcl script submits hashes to the pool, but they are all rejected!
Yeah, that branch doesn't work with CONFIG_LOOP_LOG2!=1. You probably want
http://www.makomk.com/gitweb/?p=Open-Source-FPGA-Bitcoin-Miner.git;a=summary de0-nano-hax branch, projects/DE2_115_Unoptimized_Pipelined project. The voltage regulators are also indeed horribly inefficient on the DE0-nano.