docs/machine: Generalize docs from just WiPy to other ports.

docs/library/machine.rst

@@ -18,6 +18,8 @@ Reset related functions
 
    Get the reset cause. See :ref:`constants <machine_constants>` for the possible return values.
 
+.. only:: port_wipy
+
     Interrupt related functions
     ---------------------------
 
@@ -69,9 +71,11 @@ Power related functions
 
    Stops the CPU and all peripherals including WLAN. Execution is resumed from main, just
    as with a reset. The reset cause can be checked to know that we are coming from
-   from ``machine.DEEPSLEEP``. Wake sources are ``Pin`` and ``RTC``. Current consumption 
+   ``machine.DEEPSLEEP``. Wake sources are ``Pin`` and ``RTC``. Current consumption 
    is reduced to ~5uA.
 
+.. only:: port_wipy
+
     .. function:: wake_reason()
 
         Get the wake reason. See :ref:`constants <machine_constants>` for the possible return values.
@@ -79,6 +83,8 @@ Power related functions
 Miscellaneous functions
 -----------------------
 
+.. only:: port_wipy
+
     .. function:: main(filename)
 
         Set the filename of the main script to run after boot.py is finished.  If
@@ -92,8 +98,10 @@ Miscellaneous functions
 
 .. function:: unique_id()
 
-   Returns a string of 6 bytes (48 bits), which is the unique ID of the MCU.
-   This also corresponds to the network ``MAC address``.
+   Returns a byte string with a unique idenifier of a board/SoC. It will vary
+   from a board/SoC instance to another, if underlying hardware allows. Length
+   varies by hardware (so use substring of a full value if you expect a short
+   ID). In some MicroPython ports, ID corresponds to the network MAC address.
 
 .. _machine_constants: