Mer/Documentation/Bootmenu
When flashing the new bootloader (bootmenu) via the Mer installer it will look for items in /etc/bootmenu.d/ and include those in the bootmenu. This is important when you have an operating system e.g. on your external card.
This article assumes that you booted Maemo (or equivalent) from your internal flash.
After downloading and installing the Mer installer (see Mer/Documentation/Installation) you need to work as root (see Root_access).
Go to /etc/bootmenu.d/ (cd /etc/bootmenu.d) and check for files (ls -la). Every file with the ending .item in this folder will result in an entry in the bootmenu. The internal flash is always part of the bootmenu.conf, so you dont need an entry here.
The following example (vi maemo.ext.item) will make an option in the bootmenu which allows you to boot an operating system (e.g maemo) from the 3rd partition of the external sd card, formatted with ext3:
# will be shown in the bootmenu
ITEM_NAME="Maemo on external card, p3"
# needs to be an unique string to identify this item
ITEM_ID="Maemo on external, p3"
# which hardware device and partition should be booted.
# use ${EXT_CARD} for the external card (slot) or ${INT_CARD} for the internal mmc
# followed by p3 for partition three
ITEM_DEVICE="${EXT_CARD}p3"
# which modules to load at boottime
ITEM_MODULES="mbcache jbd ext3"
# fileszstem used on that partition
ITEM_FSTYPE="ext3"
# mounting options
ITEM_FSOPTIONS="noatime,rw"