chipmisc: Add support for output pins set at runtime

Add the ability to define output pins that may be set at runtime with
a new SET_PIN extended g-code command.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/example-extras.cfg

@@ -95,28 +95,49 @@
 #   seconds.
 
 
+# Run-time configurable digital output pins (one may define any number
+# of sections with a "digital_output" prefix). Pins configured here
+# will be setup as digital outputs and one may modify them at run-time
+# using the "SET_PIN PIN=my_pin VALUE=0" extended g-code command.
+#[digital_output my_pin]
+#pin:
+#   The pin to configure as a digital output. This parameter must be
+#   provided.
+#value:
+#   The value to initially set the pin to during MCU configuration
+#   (either 0 or 1). The default is 0 (for low voltage).
+#shutdown_value:
+#   The value to set the pin to on an MCU shutdown event. The default
+#   is 0 (for low voltage).
+
 # Statically configured digital output pins (one may define any number
 # of sections with a "static_digital_output" prefix). Pins configured
-# here will be setup as a GPIO output during MCU configuration.
+# here will be setup as a GPIO output during MCU configuration. They
+# can not be changed at run-time.
 #[static_digital_output my_output_pins]
 #pins:
 #   A comma separated list of pins to be set as GPIO output pins. The
 #   pin will be set to a high level unless the pin name is prefaced
 #   with "!". This parameter must be provided.
 
-
-# Statically configured PWM output pins (one may define any number of
-# sections with a "static_pwm_output" prefix). Pins configured here
-# will be setup as PWM outputs during MCU configuration.
-#[static_pwm_output my_output_pwm]
+# Run-time configurable PWM (pulse width modulator) output pins (one
+# may define any number of sections with a "pwm_output" prefix). Pins
+# configured here will be setup as PWM outputs and one may modify them
+# at run-time using the "SET_PIN PIN=my_pin VALUE=.1" extended g-code
+# command.
+#[pwm_output my_pin]
 #pin:
-#   The pin to configure as PWM output. This parameter must be
+#   The pin to configure as a PWM output. This parameter must be
 #   provided.
 #value:
-#   The value to statically set the PWM output to. This is typically
-#   set to a number between 0.0 and 1.0 with 1.0 being full on and 0.0
-#   being full off. However, the range may be changed with the 'scale'
-#   parameter (see below). This parameter must be provided.
+#   The value to initially set the PWM output to during MCU
+#   configuration. This is typically set to a number between 0.0 and
+#   1.0 with 1.0 being full on and 0.0 being full off. However, the
+#   range may be changed with the 'scale' parameter (see below). The
+#   default is 0.
+#shutdown_value:
+#   The value to set the pin to on an MCU shutdown event. The default
+#   is 0.
 #hard_pwm:
 #   Set this value to force hardware PWM instead of software PWM. Set
 #   to 1 to force a hardware PWM at the fastest rate; set to a higher
@@ -126,14 +147,26 @@
 #   The amount of time (in seconds) per PWM cycle when using software
 #   based PWM. The default is 0.100 seconds.
 #scale:
-#   This parameter can be used to alter how the 'value' parameter is
-#   interpreted. If provided, then the 'value' parameter should be
-#   between 0.0 and 'scale'. This may be useful when configuring a PWM
-#   pin that controls a stepper voltage reference. The 'scale' can be
-#   set to the equivalent stepper amperage if the PWM were fully
-#   enabled, and then the 'value' parameter can be specified using the
-#   desired amperage for the stepper. The default is to not scale the
-#   'value' parameter.
+#   This parameter can be used to alter how the 'value' and
+#   'shutdown_value' parameters are interpreted. If provided, then the
+#   'value' parameter should be between 0.0 and 'scale'. This may be
+#   useful when configuring a PWM pin that controls a stepper voltage
+#   reference. The 'scale' can be set to the equivalent stepper
+#   amperage if the PWM were fully enabled, and then the 'value'
+#   parameter can be specified using the desired amperage for the
+#   stepper. The default is to not scale the 'value' parameter.
+
+# Statically configured PWM output pins (one may define any number of
+# sections with a "static_pwm_output" prefix). Pins configured here
+# will be setup as PWM outputs during MCU configuration. They can not
+# be changed at run-time.
+#[static_pwm_output my_output_pwm]
+#pin:
+#value:
+#hard_pwm:
+#cycle_time:
+#scale:
+#    See the 'pwm_output' section for details on these parameters.
 
 
 # Statically configured AD5206 digipots connected via SPI bus (one may