NXP Semiconductors
UM11038
OM27642 Smart Lock KIT
UM11038
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© NXP B.V. 2018. All rights reserved.
User manual
COMPANY PUBLIC
Rev. 1.1 — 11 October 2018
407611
15 of 38
8. Firmware design description
8.1 Power saving
As RFID and Bluetooth Low Energy Smart Lock Reference Design is powered by a
battery it is important that we consume as little energy as possible. The PN spends most
of its time shut down and can be woken in multiple ways:
•
over proximity touch sensor switch
•
over micro-switch – external input
•
by QN (Bluetooth Low Energy module)
QN is powered all the time and sends out Bluetooth Low Energy
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periodically so that Bluetooth Low Energy devices can discover the lock. Between
Bluetooth Low Energy advertisements broadcasts it is running in low power mode. In this
mode most peripherals are switched off and QN is running on
32 kHz clock to support RTC. PN can wake up QN from low power mode any time by
interrupt on GPIO when PN requires the current time from QNs RTC to check the token.
8.2 Interaction between PN and QN when token is delivered over RFID
When the token is delivered over RFID the PN gets powered up by means of proximity
sensor or switch and starts polling for RFID cards or NFC phones with HCE. If a device is
found it tries to retrieve the access token. After successful retrieval of the token, the
validity of the token must be checked. As time and date is required to do so, the PN must
wake up the QN to retrieve the current date and time from QNs RTC. After date/time is
retrieved from the QN and the token is deemed valid the process of unlocking the door is
started.
8.3 Interaction between PN and QN when token is delivered over
Bluetooth Low Energy
When the token is delivered over Bluetooth Low Energy, the QN powers up the PN after
a connection was established successfully between the QN and the Bluetooth Low
Energy client. Commands to retrieve the token are issued by the PN. After successful
retrieval of the token, validity of the token must be verified. If the token is deemed valid
the process of unlocking the door proceeds.