[WIP]: PX4 platform layer

[dagar]

Highlevel PX4 layers

• PX4 Modules (src/modules)
  • uORB pub/sub and parameters
  • controllers, estimators, state machines, mavlink, etc
• PX4 Drivers (src/drivers)
  • modules that access hardware
  • sensors, outputs, etc
  • platform agnostic drivers
• PX4 Libraries (src/lib)
  • used by modules and drivers
  • have access to uORB, parameters, etc
  • non-px4 libraries also exist that aren't allowed to use anything in the px4 platform (px4_add_library vs add_library)
• PX4 platform layer (src/platform)
  • uORB, parameters, hrt, work queue, task creation, px4 logging
  • defines everything in the PX4 platform layer, and implements all generic code. Depends on a significant amount of OS specific code (does it make sense for that to live under the top level os/)?
• PX4 OS support layer (os/)
  • nuttx, posix (probably linux separately), qurt
  • contains non-px4 drivers
  • should not use anything in the PX4 platform layer (parameters, logging, hrt, etc).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[dagar]

This is now obsolete with @bkueng's refactoring work, but we may want to firmly define some of these layers later.