docs/library: Note that machine.Pin.irq's hard arg may not be supported.
@@ -216,6 +216,7 @@ Methods
- ``hard`` if true a hardware interrupt is used. This reduces the delay
between the pin change and the handler being called. Hard interrupt
handlers may not allocate memory; see :ref:`isr_rules`.
+ Not all ports support this argument.
This method returns a callback object.
