u-blox 6

FXN to PM parameter mapping with "FXN On/Off Time" disabled
Power Management parameter FixNow parameter(s) Default Value
Update Period - 1000 [ms]
On-time T_on -
Search Period T_acq + T_acq_off -
Min acq.time T_acq -
Grid Offset - 0
Wait for Timefix - Disabled
Update RTC - Disabled
Update Ephemeris - Disabled
EXTINT Selection - EXTINT0
EXTINT Forces ON - Disabled
EXTINT Forces OFF - Disabled
System mode is always set to backup. If use on/off time is not enabled, update period is set to 1 s. This causes
the receiver to operate in cyclic tracking.
9.3.3.4 behavior while USB host connected
As long as the receiver is connected to a USB host, it will not enter backup state. Instead, CPU-on state is
entered. This assures that the USB specification is not violated. The drawback, however, is that power
consumption is higher.
Wake-up by pin/UART/USB is possible even if the receiver is connected to a USB host. The state of
the pin must be changed for at least one millisecond.
9.3.3.5 Cooperation with the AssistNow Autonomous feature
If both PSM and AssistNow Autonomous features are enabled, the receiver won't enter Inactive for update
state as long as AssistNow Autonomous carries out calculations. This prevents losing data from unfinished
calculations and, in the end, reduces the total extra power needed for AssistNow Autonomous. The delay
before entering Inactive for update state, if any, will be in the range of several seconds, rarely more than 20
seconds.
Only entering Inactive for update state is affected by AssistNow Autonomous. In other words: in cyclic tracking
operation, AssistNow Autonomous will not interfere with the PSM (apart from the increased power
consumption).
Enabling the AssistNow Autonomous feature will lead to increased power consumption while
prediction is calculated. The main goal of PSM is to reduce the overall power consumption.
Therefore for each application special care must be taken to judge whether AssistNow
Autonomous is beneficial to the overall power consumption or not.
9.3.4 Examples
9.3.4.1 Use Grid Offset
Scenario: Get a position fix once a day at a fixed time. If the position fix cannot be obtained try again every two
hours.
Solution: First set the update period to 24*3600s and the search period to 2*3600s. Now a position fix is
obtained every 24 hours and if the position fix fails retrials are scheduled in two hour intervals. As the update
grid is aligned to midnight Saturday/Sunday, the position fixes happen at midnight. By setting the grid offset to
12*3600s the position fixes are shifted to once a day at noon. If the position fix at noon fails, retrials take place
every two hours, the first at 14:00. Upon successfully acquiring a position fix the next fix attempt is scheduled
GPS.G6-SW-10018-A Public Release Page 24 of 201