For some reason I get this log on the console after the last reboot:
$this->bbcode_second_pass_code('', '
U-Boot SPL 2016.03-1 (Mar 17 2016 - 18:59:30)
OMAP4430 ES2.3
Trying to boot from MMC
SPL: Please implement spl_start_uboot() for your board
SPL: Direct Linux boot not active!
')
I repeated the install steps at https://archlinuxarm.org/platforms/armv7/ti/pandaboard but it didn't change anything.