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Carbon: Hardware Abstraction Layer

This directory contains board-specific implementation for the Flipper: Carbon hardware platform.

The firmware exposes API that enables libflipper to control the Carbon board's hardware peripherals. The Carbon board contains two CPUs: a microcontroller and a microprocessor.

Microcontroller (Atmel ATMEGA32U2) Firmware

The microcontroller connects to the host via USB since we wanted to keep the microprocessor's USB controller available to user applications. The microcontroller serves a number of functions.

  • Control the power (ON/OFF) and reset state of the microprocessor
  • Put the microprocessor into Device Firmware Update (DFU) mode
  • Flash new firmware images to the microprocessor and verify them
  • Halt the microprocessor and debug it using SWD (planned)
  • Allow the host to talk to the device's filesystem
  • Control the device's LED and button peripherals
  • Send message runtime packets to the microprocessor
  • Pass printf messages sent by the microprocessor back to the host

Microprocessor (Atmel ATSAM4S16BA) Firmware

The microprocessor is the main CPU on the device.

  • Load and run programs
  • Schedule the execution of multiple running programs
  • Communicate with the device's hardware peripherals
  • Interact with backpacks plugged into the expansion connector

HAL

The Hardware Abstraction Layer (HAL) exposes the Carbon hardware as a struct _lf_device * that can be interacted with by libflipper.

  • Scan the USB bus using libusb to find boards with the VID/PID combo of Carbon. Get a list of the struct _lf_endpoint *s corresponding to the attached devices.
  • Iterate through this list of endpoints and create a new struct _lf_device * for each of them. This is the U2 device.
  • Create a new struct _lf_endpoint * to be used as the bridge endpoint and configure it to use the U2 device's uart0 module.
  • Create a new struct _lf_device * using this bridge endpoint. This will be the 4S device.
  • Return the 4S device as the attached device.