Unless you can set the order of the usb devices (don't think i've seen that in a bios), then no...
but i aint talking about necessarily booting from the SD... well sorta... but only the bootloader, grub
If you leave the SD in all the time, then you can install the bootloader only to it, and have it boot whichever drive you want to boot... another option is a differant boot loader on the SD... i seen one on a floppy that says on boot when the (non bootable) floppy is left in "You accidentally left the floppy in the drive, booting from hard disk".
It prevents the "Non system disk" error and just skips itself... shouldn't be too hard to "dd" the bootsector from this type of floppy and then "dd" it back to the SD card.
The reboot loop you are getting now is because the SD is the 1st boot device and with media in it, it is selected for boot, doesn't, then the machine reboots to try again... dunno why you aint getting the non system disk error though.
I'll try to hunt for that boot sector that bypasses itself...
EDIT: here is a page that talks about said sector...http://www.paulcilwa.com/writing/technical/03.assembler/BootSector/index.asp
EDIT2: Ok, i found the bootsector i was talking about, it was from winimage... he uses one written by C.H. Hochstatter... which has a freeware tool fdformat on simtel
Using this, vfd(virtual floppy drive), and dd for windows... i formatted a floppy with it, then extracted the 512 byte bootsect.bin
then proceeded to write it back to an SD card...
dd if=bootsect.bin of=/dev/sd_card bs=512 count=1
explanation of the previous command:
- dd - the command in linux
- if - input file (in this case bootsect.bin
- of - output file (in this case the device for my sd card)
- bs - block size (512 bytes, the size of the bootsector)
- count - 1, for 1 block, don't wanna ruin the rest of the disks data
Then i proceeded to set my boot order to USB, floppy, CD...
on reboot in a mchine with only a multi card reader and a usb hard disk attached and SD card in the slot i got this:
Would this work for you?