Expansion decks turned off for faster charging

[knmcguire]

Some expansion decks draw a lot of power which will affect the charging time. Maybe it would be good to turn them off somehow with some define?

Based on the discussion going on here: https://forum.bitcraze.io/viewtopic.php?f=5&t=4311&p=19822#p19822

[jonasdn]

This was discussed in the office, some notes from that discussion:

Problem statements

• Charging with some decks active will take a long time since the decks are power hungry
• It is today not possible to turn off the expansion decks without also turning off the stm32 MCU at the same time
• The Crazyflie will charge its battery while turned off (the charging chip is active) but only at 100mA as opposed to 500mA
  • This is because to get 500mA you need to negotiate with the USB port and that is done by the nrf chip
  • The charging is not indicated in anyway today, since no chip with control over LEDs is awake

Possible solutions

1. We could send a message to the nrf chip from the stm32 asking it to shutdown the stm32 and expansion deck (SYSLINK_PM_ONOFF_SWITCHOFF)

   • This would need some plumbing to make possible for a user to do:
     • A parameter?
     • CRTP message?
   • We would still not have any indication of charge, should we:
     • Blink with the nrf led (M2) while charging?
     • Blink with the nrf led in some pattern when message is received?
     • Do nothing?
   1. Always do 500mA in off-mode, regardless of negotiation
      • So you could, as a user, turn off the Crazyflie using button while charging, to charge faster
      • Would still not have any indication, and nrf chip is off as well, so no means of LED flashing

2. Have a special mode in nrf when cable is detected so it does not turn off, so it can keep charging at 500mA (480mA, since nrf takes 20mA)

   • Same charge indication problems as in 1.

Did I miss anything @krichardsson, @evoggy, @tobbeanton ? Any thougts @knmcguire @ataffanel ?

[jonasdn]

The way forward right now, we think, is option 3. we will update the NRF firmware to always do 500mA charging, this will allow you to charge fast always, by turning the crazyflie off.