STM32F4 Discovery, RTC and GPS PPS synchronisation

Goal:
I want to accurately update the STM32F4 RTC:

• using a GPS pulse per second (PPS) signal or
  
• using the GPS RTC as external reference clock
  
  

Some background:

I am using the following hardware

1. STM32F4 Discovery board
   
2. MikroElektronika STM32F4 Discovery shield
   
3. MikroElektronika GPS click board (ublox LEA-6S receiver)
   
   

which pretty much looks like this:

So far I have integrated the GPS receiver into my project pretty well and have extended the basic GPS module to include configuration commands and a few other features.

The STM32F407 has a highly capable, built-in RTC which I would like to make use of within the Espruino JavaScript environment.

For the inquisitive, the ST manual on how to use the RTC can be found here.

From what I can see I have the following options to synchronise the STM32F4 RTC:

• The RTC calendar can be synchronized to a more precise, remote clock using the RTC shift feature (see page 19 of the ST RTC manual for more details).
  
• Use the "zero on write" method as described in the "Clock Synchronisation Methods" link below.
  
• Figure out RFC2783 and RFC1589 and hack something using the PPS signal (as used in the gpsd Linux project).
  
• Hack something according to the IEEE1588 Precision Time Protocol.
  
  

Questions:

1. I'd appreciate some guidance on how to expose the functionality contained in stm32f4xx_rtc.c to the Espruino JavaScript interpreter.
   
2. Has anybody tried to synchronise the RTC to a more precise, external time source and is willing to share some tips?
   
   

References:
Here are a few interesting links that have edified me somewhat:

• Clock Synchronisation Methods
  
• Time synchronization with a Garmin GPS
  
• Syncing Arduino with GPS time
  
• Synchronizing and Correlating Measurements to a Global Timebase with GPS
  
• Testing and Verifying Time Synchronization