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Fobnail blink codes

One of the main advantages of using hardware dongle for attestation is that it can report the state to users without relying on proper functioning of PC (or another device) being attested. This is done by various blink codes representing different states of Fobnail Token operation.

nRF52840 dongle LEDs location

Even though LED2 on nRF52840 dongle is a multicolor RGB LED, Fobnail only uses red in order to not exclude users with impaired color vision. LED1 is green. Unless noted otherwise, short blinks and intervals between blinks take 100 ms.

Idle states

Token not provisioned

Red LED will be lit indefinitely.

Token provisioned, waiting for CoAP client

Both LEDs will shortly blink every 5 seconds. Cycle starts with blink, followed by a waiting period, so any LED failure should be visible when provisioned Token is connected to the device.

Fobnail provisioning

On successful Token provisioning, green LED will blink once. No change on failure, i.e. red light will be kept on.

Platform provisioning

On successful platform provisioning, green LED will blink three times, then Token goes back to waiting state. On failure no signal will be given, the Token will stay in waiting state and will keep blinking both LEDs every 5 seconds.


Note that Fobnail is exposed to OS as network device. As such, there may be multiple clients connected to it, even from another devices in local network, assuming proper (or improper, depending on use case) routing. One implication is that following states are not mutually exclusive, success and failure may be reported simultaneously.


Green LED will be lit as long as any successfully attested client is connected and has access to Fobnail Token Services. Client is considered disconnected after 3 seconds of inactivity.


Red LED will be lit for 5 seconds.