From 40f834d58fee1daa406f0f9edf01e393b3eb7f76 Mon Sep 17 00:00:00 2001
From: Ron Evans <ron@hybridgroup.com>
Date: Tue, 18 Sep 2018 15:02:38 +0200
Subject: [PATCH] avr: ADC with 0-1023 range

---
 src/examples/adc/adc.go       | 29 +++++++++++++++++++++++
 src/examples/serial/serial.go | 10 --------
 src/machine/machine.go        |  4 ++++
 src/machine/machine_avr.go    | 44 +++++++++++++++++++++++++++++++++++
 4 files changed, 77 insertions(+), 10 deletions(-)
 create mode 100644 src/examples/adc/adc.go
 delete mode 100644 src/examples/serial/serial.go

diff --git a/src/examples/adc/adc.go b/src/examples/adc/adc.go
new file mode 100644
index 00000000..8d1a9f4d
--- /dev/null
+++ b/src/examples/adc/adc.go
@@ -0,0 +1,29 @@
+package main
+
+import (
+	"machine"
+	"time"
+)
+
+// This example assumes that an analog sensor such as a rotary dial is connected to pin ADC0.
+// When the dial is turned past the midway point, the built-in LED will light up.
+
+func main() {
+	machine.InitADC()
+
+	led := machine.GPIO{machine.LED}
+	led.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+
+	sensor := machine.ADC{machine.ADC2}
+	sensor.Configure()
+
+	for {
+		val := sensor.Get()
+		if val < 512 {
+			led.Low()
+		} else {
+			led.High()
+		}
+		time.Sleep(time.Millisecond * 100)
+	}
+}
diff --git a/src/examples/serial/serial.go b/src/examples/serial/serial.go
deleted file mode 100644
index b0dd403f..00000000
--- a/src/examples/serial/serial.go
+++ /dev/null
@@ -1,10 +0,0 @@
-package main
-
-import "time"
-
-func main() {
-	for {
-		println("hello world!")
-		time.Sleep(time.Second)
-	}
-}
diff --git a/src/machine/machine.go b/src/machine/machine.go
index bc8e14cd..094b4b59 100644
--- a/src/machine/machine.go
+++ b/src/machine/machine.go
@@ -19,3 +19,7 @@ func (p GPIO) Low() {
 type PWM struct {
 	Pin uint8
 }
+
+type ADC struct {
+	Pin uint8
+}
diff --git a/src/machine/machine_avr.go b/src/machine/machine_avr.go
index dd46f15a..d338af1d 100644
--- a/src/machine/machine_avr.go
+++ b/src/machine/machine_avr.go
@@ -124,3 +124,47 @@ func (pwm PWM) Set(value uint16) {
 		panic("Invalid PWM pin")
 	}
 }
+
+// ADC on the Arduino
+const (
+	ADC0 = 0
+	ADC1 = 1
+	ADC2 = 2
+	ADC3 = 3
+	ADC4 = 4
+	ADC5 = 5
+)
+
+// InitADC initializes the registers needed for ADC.
+func InitADC() {
+	// set a2d prescaler so we are inside the desired 50-200 KHz range at 16MHz.
+	*avr.ADCSRA |= (avr.ADCSRA_ADPS2 | avr.ADCSRA_ADPS1 | avr.ADCSRA_ADPS0)
+
+	// enable a2d conversions
+	*avr.ADCSRA |= avr.ADCSRA_ADEN
+}
+
+// Configure configures a ADCPin to be able to be used to read data.
+func (a ADC) Configure() {
+	return // no pin specific setup on AVR machine.
+}
+
+// Get returns the current value of a ADC pin. The AVR will return a 10bit value ranging
+// from 0-1023.
+func (a ADC) Get() uint16 {
+	// set the analog reference (high two bits of ADMUX) and select the
+	// channel (low 4 bits), masked to only turn on one ADC at a time.
+	// this also sets ADLAR (left-adjust result) to 0 (the default).
+	*avr.ADMUX = avr.RegValue(avr.ADMUX_REFS0 | (a.Pin & 0x07))
+
+	// start the conversion
+	*avr.ADCSRA |= avr.ADCSRA_ADSC
+
+	// ADSC is cleared when the conversion finishes
+	for ok := true; ok; ok = (*avr.ADCSRA & avr.ADCSRA_ADSC) > 0 {
+	}
+
+	low := uint16(*avr.ADCL)
+	high := uint16(*avr.ADCH)
+	return uint16(low) | uint16(high<<8)
+}