user38851: For some applications I need access to the registers that control the output/input and high/low state of pins.  For example pin 10 on a adalogger is PORTB with a mask of _BV(6).  This information can be found in pins_arduino.h.  For some boards many variants get installed.  I turned on verbose compiling and looked through the output there as well as looking through boards.txt and platform.txt.  In that output I see an include to a directory with a pins_arduino.h file but there is nothing in that file but a definition for BUILTIN_LED.
When I run a function like digitalWrite(13,HIGH); how does it know which registers to use for pin 13?  Since my board has this pin, and digitalWrite(13, HIGH); makes an LED light up ... it's working.

user4143: In the boards.txt file for the core in question you have a line for each board:
xxxx.build.variant=yyyy

where yyyy is the name of the folder in variants for the board.
For instance, the Uno, has:
uno.build.variant=standard

which relates to:
variants/standard

with the pins_arduino.h file in it for that board.

38851: <p>For some applications I need access to the registers that control the output/input and high/low state of pins.  For example pin 10 on a adalogger is <code>PORTB</code> with a mask of <code>_BV(6)</code>.  This information can be found in <code>pins_arduino.h</code>.  For some boards many variants get installed.  I turned on verbose compiling and looked through the output there as well as looking through <code>boards.txt</code> and <code>platform.txt</code>.  In that output I see an include to a directory with a <code>pins_arduino.h</code> file but there is nothing in that file but a definition for <code>BUILTIN_LED</code>.</p>

<p>When I run a function like <code>digitalWrite(13,HIGH);</code> how does it know which registers to use for pin 13?  Since my board has this pin, and <code>digitalWrite(13, HIGH);</code> makes an LED light up ... it's working.</p>
 4143: <p>In the boards.txt file for the core in question you have a line for each board:</p>

<pre><code>xxxx.build.variant=yyyy
</code></pre>

<p>where yyyy is the name of the folder in variants for the board.</p>

<p>For instance, the Uno, has:</p>

<pre><code>uno.build.variant=standard
</code></pre>

<p>which relates to:</p>

<pre><code>variants/standard
</code></pre>

<p>with the <code>pins_arduino.h</code> file in it for that board.</p>
