ErikZalm/Marlin — pull request #456 by Stefanowicz (2013-04-24 08:56:16+00:00)
Title: Add (as an option) slower SD transfer mode

When using slow 5V -> 3.3V buffer and/or slow SD card(?) you'll get volume init error. Limiting SPI speed solves the problem.
I've found that it isn't only my problem so I added an option #SDSLOW.