Original date: 2022-08-19

Related tweets: [1] [2]

The RF test PCB was submitted to the PCB factory. In the meantime, I was trying to redesign the architecture to mitigate the problems of the current design:

• Power consumption is not low enough
  • It can't even reach the standby time of the original Nokia 168x now
• Physical difficulties
  • Frequent kernel/rootfs changes are needed in the development stage. But currently it's really inconvenient to push the RESET button (which is behind the battery) and the BOOT0 button (which is the left func key of the keypad) at the same time.
  • The only UART connection is the 3 tiny little pads on the PCB. It would be hugely better if the serial console can be controlled via a built-in USB to UART.
• Multiple missing Linux drivers
  • Many drivers isn't working properly

So, the idea is to use a ultra low power MCU to act as the "EC" of this device. It's exactly the same definition of the "EC" in your PC or laptop. The MCU is supposed to do these things:

• Extended power management
  • Controls the power supply of individual components on the board
• Handle all LoRa communications
  • Power to the X1000 can be shut off entirely in standby mode
• Keypad polling
  • Spares a PCA9555
• Act as a USB to UART bridge
  • Life is a lot easier!
• Control the RESET and BOOTx lines of the X1000
  • Boot device selection can be achieved using a USB CDC console then