Got the firmware to compile and produce something vaguely sensible.

firmware/docs/implementation-notes.adoc

@@ -1,6 +1,6 @@
 Motion control in an interrupt.
 
-= Parts
+== Parts
 This consists of two parts, the planner and the executor.
 
 The planner receives target positions. Each time it receives a target
@@ -13,7 +13,7 @@ the step lines of the MCU.
 
 These two processes communicate by means of a command queue.
 
-== Executor
+=== Executor
 1. Update a cycle counter
 2. Evaluates the next output of the position polynomial (3 adds)
 3. determine whether to toggle a stepper, and do so.
@@ -21,7 +21,7 @@ These two processes communicate by means of a command queue.
 
 
 
-== Command queue
+=== Command queue
 
 The command queue takes the form of a ring buffer, with each item
 containing a motion segment.  The ring buffer must be large enough to
@@ -40,9 +40,9 @@ A motion profile segment consists of the following values:
 The following invariants hold for the command queue:
 
 
-== Planner
+=== Planner
 
-=== Aborting
+==== Aborting
 
 In case of an abort, the fastest stop profile will consist of at most
 3 segments: const -jerk to max -a, const -a to to lead-out, const +j