docs/library/pyb.Timer: Document `brk` argument and its constants.

docs/library/pyb.Timer.rst

@@ -62,7 +62,7 @@ Constructors
 Methods
 -------
 
-.. method:: Timer.init(*, freq, prescaler, period, mode=Timer.UP, div=1, callback=None, deadtime=0)
+.. method:: Timer.init(*, freq, prescaler, period, mode=Timer.UP, div=1, callback=None, deadtime=0, brk=Timer.BRK_OFF)
 
    Initialise the timer.  Initialisation must be either by frequency (in Hz)
    or by prescaler and period::
@@ -107,6 +107,12 @@ Methods
        measures ticks of ``source_freq`` divided by ``div`` clock ticks.
        ``deadtime`` is only available on timers 1 and 8.
 
+     - ``brk`` - specifies if the break mode is used to kill the output of
+       the PWM when the ``BRK_IN`` input is asserted. The value of this
+       argument determines if break is enabled and what the polarity is, and
+       can be one of ``Timer.BRK_OFF``, ``Timer.BRK_LOW`` or
+       ``Timer.BRK_HIGH``.
+
     You must either specify freq or both of period and prescaler.
 
 .. method:: Timer.deinit()
@@ -271,3 +277,9 @@ Constants
           Timer.CENTER
 
    Configures the timer to count Up, Down, or from 0 to ARR and then back down to 0.
+
+.. data:: Timer.BRK_OFF
+          Timer.BRK_LOW
+          Timer.BRK_HIGH
+
+   Configures the break mode when passed to the ``brk`` keyword argument.