adc_scaled: Add support for Duet2 Maestro "vref monitoring"

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

config/example-extras.cfg

@@ -2222,6 +2222,23 @@
 #   communication. The pin must have a valid pinmux configuration
 #   for the given SERCOM peripheral. This parameter must be provided.
 
+# Duet2 Maestro analog scaling by vref and vssa readings. Defining an
+# adc_scaled section enables virtual adc pins (such as "my_name:PB0")
+# that are automatically adjusted by the board's vref and vssa
+# monitoring pins. Be sure to define this config section above any
+# config sections that use one these virtual pins.
+#[adc_scaled my_name]
+#vref_pin:
+#   The ADC pin to use for VREF monitoring. This parameter must be
+#   provided.
+#vssa_pin:
+#   The ADC pin to use for VSSA monitoring. This parameter must be
+#   provided.
+#smooth_time: 2.0
+#   A time value (in seconds) over which the vref and vssa
+#   measurements will be smoothed to reduce the impact of measurement
+#   noise. The default is 2 seconds.
+
 # Replicape support - see the generic-replicape.cfg file for further
 # details.
 #[replicape]

config/generic-duet2-maestro.cfg

@@ -59,6 +59,11 @@ microsteps: 16
 run_current: 0.800
 stealthchop_threshold: 30
 
+# Support analog sensor adjustments using VREF/VSSA pins
+[adc_scaled vref_scaled]
+vref_pin: PA17
+vssa_pin: PA19
+
 [extruder]
 step_pin: PC4
 dir_pin: PB7
@@ -69,7 +74,7 @@ filament_diameter: 1.750
 heater_pin: !PC1
 sensor_type: EPCOS 100K B57560G104F
 pullup_resistor: 2200
-sensor_pin: PB0
+sensor_pin: vref_scaled:PB0
 control: pid
 pid_Kp: 22.2
 pid_Ki: 1.08
@@ -110,7 +115,7 @@ stealthchop_threshold: 5
 heater_pin: !PC0
 sensor_type: EPCOS 100K B57560G104F
 pullup_resistor: 2200
-sensor_pin: PA20
+sensor_pin: vref_scaled:PA20
 control: watermark
 min_temp: 0
 max_temp: 130