How to create a WiFi ad-hoc connection with wpa_supplicant

Using the following /etc/wpa_supplicant.conf :

ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=0
fast_reauth=1
update_config=1

## -- Example AD-HOC network
ap_scan=2       # mandatory for AD-HOC mode
network={
        mode=1
        ssid="adhoc_network"
        frequency=2432
        key_mgmt=NONE
}

e.g. with fixed IPs on both sides allows to communicate without access point between two Wi-ME 9210.
It should also work on Wi-i.MX51/53 using Redpine chip.

The instructions from Digi Embedded Linux documentation section 10.8.1.2 using wpa_cli seem not to be complete, since at least one of the devices should define a channel or frequency. see also https://wiki.archlinux.org/index.php/ad-hoc_networking

The Atheros AR6x03 driver/chip in the Wi-i.MX28/Wi-i.MX6 does not support Ad-hoc mode, it supports Wi-Fi Direct instead