--- a/FC-handset-spec	Thu Jun 10 18:10:35 2021 +0000
+++ b/FC-handset-spec	Thu Jun 10 19:08:05 2021 +0000
@@ -406,3 +406,49 @@
 not going to use Iota LEDB, and shall only use MAX1916 instead.  We also gain a
 functional improvement over Pirelli DP-L10 by using MAX1916: our keypad
 backlight intensity will remain the same over the battery discharge range.
+
+1.6. Side buttons
+
+In addition to the 21-button main keypad, our FC Libre Dumbphone handset will
+include 3 side buttons: two on the left side, intended for volume up/down
+control, and one on the right side, serving auxiliary functions.  This side
+button arrangement is identical to TI's D-Sample and similar to Pirelli DP-L10:
+the only difference between our arrangement (matching D-Sample) and Pirelli's
+is that Pirelli moved the 3rd side button to the left and designated it as the
+camera button.  However, we (FreeCalypso) have no interest in ever implementing
+any kind of camera on our phones, hence we are moving the 3rd side button back
+to where it was in TI's original design (on the right), and we will use it for
+purposes of our own invention.
+
+The starting point UI code we got from TI does not do anything with the right
+side button (even though this button exists and works on the D-Sample platform
+on which this code was originally developed), hence we have full freedom to
+invent our own uses for it.  The following uses are envisioned:
+
+* Long press of this button may be our way of turning the hands-free loudspeaker
+  on and off, a function that does not exist in the starting point UI code from
+  TI.
+
+* When the phone is in its normal idle standby operation (not in a call and not
+  being poked at by the user, but registered to a GSM network and ready to
+  accept incoming calls or SMS), the display will be off.  Users often desire
+  to check the time and other status (check coverage, see if they missed any
+  calls or SMS), which will require pressing any button to turn on the display.
+  At that point a 30 s timer kicks in, which will turn the display back off
+  after 30 s of inactivity.  However, an argument can be made that keeping the
+  display on for 30 s if the user only wanted to quickly glance at the time is
+  a waste of battery.  Here is one proposed solution: we can implement a
+  function where a short press of the right side button when the phone is on its
+  idle screen will cause the display to turn off immediately and activate the
+  keyguard.  The user can then press the right side button once to turn on the
+  display and look at it, and then press the same button again to turn it back
+  off.
+
+* When we are in a long call, the LCD backlight does not turn off completely,
+  instead it will go dim - but still readable.  Any button presses in this state
+  are NOT swallowed - they take their regular actions.  However, the keypad
+  backlight turns off fully in this state, and under certain conditions (like
+  out at night) the user may not be able to see the keypad.  If a short press
+  of the right side button invokes no other action besides switching on full
+  display brightness and the keypad backlight, this right side button can be
+  found by touch, and thus solve this particular problem case.