In case someone is interested, here is a bit improved BIOS for OCM. You can boot to 50Hz by holding down "H" on boot and you can save RTC setting by executing RTCSAVE.COM

Installation:
- Download new BIOS
- Format SD/MMC card
- Copy MSXBIOS.DAT as first file in the card
- If you want to change RTC-settings, copy RTCSAVE.COM to somewhere

(Tested with original hardware version supplied inside the OCM when shipped from factory)

Ah, I forgot to include this: (added license.txt to packet)

-- ESE MSX-SYSTEM3 / MSX clone on a Cyclone FPGA (ALTERA)
-- Revision 1.00
--
-- Copyright (c) 2006 Kazuhiro Tsujikawa (ESE Artists' factory)
-- Copyright (c) 2006 D4 Enterprise,Inc.
-- Copyright (c) 2006 MSX association
-- All rights reserved.
--
-- Redistribution and use of this source code or any derivative works, are
-- permitted provided that the following conditions are met:
--
-- 1. Redistributions of source code must retain the above copyright notice,
-- this list of conditions and the following disclaimer.
-- 2. Redistributions in binary form must reproduce the above copyright
-- notice, this list of conditions and the following disclaimer in the
-- documentation and/or other materials provided with the distribution.
-- 3. Redistributions may not be sold, nor may they be used in a commercial
-- product or activity without specific prior written permission.
--
-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-- "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
-- TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
-- PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
-- CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
-- EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-- PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
-- OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
-- WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
-- OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
-- ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

At last! Some RTC workaround for OneChipMSX. Thanks NYYRIKKI!