To flash a Meraki AP from their firmware see http://wiki.openwrt.org/OpenWrtDocs/Hardware/Meraki/Mini for lots of information.
To get the redboot command, set computer IP to 192.168.84.9 and telnet to 192.168.84.1:9000, wait for the second LED to come on after light up, and then flash 4 times and start telnet session. If you miss the 2 second window just retry.
Once you have a redboot command prompt run the following commands (the first three are possibly optional, but all were run to flash our Merakis. In total this process from start to finish should take just under half an hour)
fis create -b 0x80041000 -l 0x100000 -f 0xa8050000 -e 0x80041000 -r 0x80041000 -n /storage fis create -b 0x80041000 -l 0x340000 -f 0xa8150000 -e 0x80041000 -r 0x80041000 -n linux fis create -b 0x80041000 -l 0x340000 -f 0xa8490000 -e 0x80041000 -r 0x80041000 -n rootfs
Then to format run
fis init
Load the openwrt firmware etc...(requires TFTP server)
load -r -b 0x80041000 -m tftp -h 192.168.84.9 openwrt-atheros-2.6-vmlinux.gz fis create -r 0x80041000 -l 0x180000 -e 0x80041000 linux load -r -b 0x80041000 -m tftp -h 192.168.84.9 openwrt-atheros-2.6-root.jffs2-64k fis create -r 0x80041000 -l 0x620000 rootfs
Then configure the boot script to run linux and execute it.
RedBoot> fconfig -d boot_script_data boot_script_data: .. whatever it currently is Enter script, terminate with empty line >> fis load -d linux >> exec >> Update RedBoot non-volatile configuration - continue (y/n)? y
Then unplug it and plug it back in again. The first time it starts up it will take about 40 seconds to decompress and run. See OpenWRT for first boot details.