docs/library: Specify additional ADC methods and new ADCBlock class.

The new ADC methods are: init(), read_uv() and block().

The new ADCBlock class has methods: init() and connect().

See related discussions in adafruit#3943, adafruit#4213.

Signed-off-by: Damien George <damien@micropython.org>

docs/library/machine.ADC.rst

@@ -8,28 +8,59 @@ The ADC class provides an interface to analog-to-digital convertors, and
 represents a single endpoint that can sample a continuous voltage and
 convert it to a discretised value.
 
+For extra control over ADC sampling see :ref:`machine.ADCBlock <machine.ADCBlock>`.
+
 Example usage::
 
-   import machine
+   from machine import ADC
 
-   adc = machine.ADC(pin)   # create an ADC object acting on a pin
-   val = adc.read_u16()     # read a raw analog value in the range 0-65535
+   adc = ADC(pin)        # create an ADC object acting on a pin
+   val = adc.read_u16()  # read a raw analog value in the range 0-65535
+   val = adc.read_uv()   # read an analog value in microvolts
 
 Constructors
 ------------
 
-.. class:: ADC(id)
+.. class:: ADC(id, *, sample_ns, atten)
 
    Access the ADC associated with a source identified by *id*.  This
    *id* may be an integer (usually specifying a channel number), a
    :ref:`Pin <machine.Pin>` object, or other value supported by the
    underlying machine.
 
+   If additional keyword-arguments are given then they will configure
+   various aspects of the ADC.  If not given, these settings will take
+   previous or default values.  The settings are:
+
+     - *sample_ns* is the sampling time in nanoseconds.
+
+     - *atten* specifies the input attenuation.
+
 Methods
 -------
 
+.. method:: ADC.init(*, sample_ns, atten)
+
+   Apply the given settings to the ADC.  Only those arguments that are
+   specified will be changed.  See the ADC constructor above for what the
+   arguments are.
+
+.. method:: ADC.block()
+
+   Return the :ref:`ADCBlock <machine.ADCBlock>` instance associated with
+   this ADC object.
+
+   This method only exists if the port supports the
+   :ref:`ADCBlock <machine.ADCBlock>` class.
+
 .. method:: ADC.read_u16()
 
    Take an analog reading and return an integer in the range 0-65535.
    The return value represents the raw reading taken by the ADC, scaled
    such that the minimum value is 0 and the maximum value is 65535.
+
+.. method:: ADC.read_uv()
+
+   Take an analog reading and return an integer value with units of
+   microvolts.  It is up to the particular port whether or not this value
+   is calibrated, and how calibration is done.

docs/library/machine.ADCBlock.rst

@@ -0,0 +1,58 @@
+.. currentmodule:: machine
+.. _machine.ADCBlock:
+
+class ADCBlock -- control ADC peripherals
+=========================================
+
+The ADCBlock class provides access to an ADC peripheral which has a
+number of channels that can be used to sample analog values.  It allows
+finer control over configuration of :ref:`machine.ADC <machine.ADC>`
+objects, which do the actual sampling.
+
+This class is not always available.
+
+Example usage::
+
+   from machine import ADCBlock
+
+   block = ADCBlock(id, bits=12)  # create an ADCBlock with 12-bit resolution
+   adc = block.connect(4, pin)    # connect channel 4 to the given pin
+   val = adc.read_uv()            # read an analog value
+
+Constructors
+------------
+
+.. class:: ADCBlock(id, *, bits)
+
+   Access the ADC peripheral identified by *id*, which may be an integer
+   or string.
+
+   The *bits* argument, if given, sets the resolution in bits of the
+   conversion process.  If not specified then the previous or default
+   resolution is used.
+
+Methods
+-------
+
+.. method:: ADCBlock.init(*, bits)
+
+   Configure the ADC peripheral.  *bits* will set the resolution of the
+   conversion process.
+
+.. method:: ADCBlock.connect(channel)
+            ADCBlock.connect(source)
+            ADCBlock.connect(channel, source)
+
+   Connect up a channel on the ADC peripheral so it is ready for sampling,
+   and return an :ref:`ADC <machine.ADC>` object that represents that connection.
+
+   The *channel* argument must be an integer, and *source* must be an object
+   (for example a :ref:`Pin <machine.Pin>`) which can be connected up for sampling.
+
+   If only *channel* is given then it is configured for sampling.
+
+   If only *source* is given then that object is connected to a default
+   channel ready for sampling.
+
+   If both *channel* and *source* are given then they are connected together
+   and made ready for sampling.

docs/library/machine.rst

@@ -199,6 +199,7 @@ Classes
    machine.Pin.rst
    machine.Signal.rst
    machine.ADC.rst
+   machine.ADCBlock.rst
    machine.PWM.rst
    machine.UART.rst
    machine.SPI.rst