.. include:: <mmlalias.txt>


Firmware: Emit CAN "State Change Notification" Frames
=====================================================

Requirements Specification
--------------------------

* Use :doc:`../can-jf0815-hw/index`
* On every state transition, send out the new state
* CAN ID: 37
* Payload, in little endian:

  * ``RUNNING``: 1
  * ``OVERTEMP``: 2
  * ``SENSORBURNING``: 3

Plan
----

* FSM constructor: add "CAN id", and "CAN interface" (Linux SocketCAN) parameters
* Add ``CAN_JF0815_HW_Wrapper`` member
* ``CAN_JF0815_HW_Wrapper`` only has room for one in-flight frame

  * |longrightarrow| Need "pending" queue if still busy sending

* Wrap state change into method

  * Create CAN frame like defined
  * If xmit busy, push to pending-queue
  * Else, xmit directly
  * Change state

* Register ISR for "xmit-done" interrupt

  * Pop frame from pending queue if any, and xmit
  * **Question: locking?**

Software Changes When Done
--------------------------

.. toctree::
   :maxdepth: 1

   main
   fsm

Fear And Uncertainty Ahead
--------------------------

**Pending Queue**

* "Pending queue" is hammered on by multiple ISRs **in parallel**
* ``std::list`` is **not atomic**
* |longrightarrow| **Fortunately we are using a spinlock**

**If-then-else**

* ``if (controller is busy)``, followed by action, **is not atomic**
* Once we enter the *controller busy* branch (about to enqueue the
  frame for later), the CAN xmit-done ISR might have just interrupted
  us
* |longrightarrow| **Lost/delayed notification**
* |longrightarrow| **Fortunately we are using a spinlock**