Without resetting the FPU we get spurious failures in Pycardium.  These
manifest in many different forms, ranging from HardFaults and triggered
assertions to "syntax errors" in loaded scripts while said script does
not contain any.

These failures stem from the FPU still containing state from the last
loaded payload and thus sometimes corrupting stack locations where the
previous payload had floating point state.

Closes #72.

Signed-off-by: Rahix <rahix@rahix.de>

When a load fails early and core 1 continues to loop in the reset stub,
Epicardium might lock up when sending an interrupt and waiting for the
API_CALL_MEM->int_id to be reset.

Signed-off-by: Rahix <rahix@rahix.de>

This commit introduces a lifecycle for core 1.  Based on the new loading
system, a few APIs are made available to control the payload running on
core 1.  These are:

1. From core 1 (Pycardium, L0dable):

    - `epic_exec(name)` API Call:  Request loading of a new payload by
      name.  If the file does not exist, the call will return with an
      error code.  Otherwise, control will go to the new payload.
    - `epic_exit(retcode)` API Call:  Return from payload
      unconditionally.  This call should be called whenever a payload is
      done or when it has hit an unrecoverable error.  On `epic_exit`,
      Epicardium will reset the core back into the menu.

2. From inside Epicardium:

    - `epic_exec(name)`: This is **not** the same as the API call, as it
      needs a different implementation underneath.  It will load a new
      payload and wait until this load actually completed (synchroneous).
    - `return_to_menu()`: Return core 1 to the menu script no matter
      what it is currently doing.  This call is asynchroneous and will
      return immediately after scheduling the lifecycle task.  This task
      will then take care of actually performing the load.

Signed-off-by: Rahix <rahix@rahix.de>

This commit introduces a way to control core 1.  This is archieved by a
predefined API-Interrupt:  The reset interrupt.  When triggered, it will
bring the core back into its default state and wait for a new vector
address from Epicardium.  Once this vector address is transferred, it
will start the new payload.

This method only works as long as core 1 is responsive to the API
interrupts.  Cases where this might not be the case:

  - During times where core 1 has interrupts disabled
  - When in a higher priority exception handler
  - When core 1 has corrupted its IVT

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Previously 0 was used but as 0 is also the ID of the reset interrupt,
this could lead to weird behaviors.

Signed-off-by: Rahix <rahix@rahix.de>

This allows pycardium to learn which script it should start once it
boots.  Arguments can only be read before any API calls are made.
Afterward they are lost.

To ensure they won't collide with anything during a core 1 restart,
they are offset by 0x20 from the start of the API buffer.

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>