Pico adc input ch support (#2737)

machine/rp2040: ADC changes, including
* Add rp2040 ADC mux channel support. Internal temp sensor reading and fix for incorrect setting of CS.AINSEL reg bits
* Reset ADC ref voltage in InitADC

Author: lincolngill

src/examples/adc_rp2040/adc.go

@@ -0,0 +1,49 @@
+// Reads multiple rp2040 ADC channels concurrently. Including the internal temperature sensor
+
+package main
+
+import (
+	"fmt"
+	"machine"
+	"time"
+)
+
+type celsius float32
+
+func (c celsius) String() string {
+	return fmt.Sprintf("%4.1f℃", c)
+}
+
+// rp2040 ADC is 12 bits. Reading are shifted <<4 to fill the 16-bit range.
+var adcReading [3]uint16
+
+func readADC(a machine.ADC, w time.Duration, i int) {
+	for {
+		adcReading[i] = a.Get()
+		time.Sleep(w)
+	}
+}
+
+func main() {
+	machine.InitADC()
+	a0 := machine.ADC{machine.ADC0} // GPIO26 input
+	a1 := machine.ADC{machine.ADC1} // GPIO27 input
+	a2 := machine.ADC{machine.ADC2} // GPIO28 input
+	t := machine.ADC_TEMP_SENSOR    // Internal Temperature sensor
+	// Configure sets the GPIOs to PinAnalog mode
+	a0.Configure(machine.ADCConfig{})
+	a1.Configure(machine.ADCConfig{})
+	a2.Configure(machine.ADCConfig{})
+	// Configure powers on the temperature sensor
+	t.Configure(machine.ADCConfig{})
+
+	// Safe to read concurrently
+	go readADC(a0, 10*time.Millisecond, 0)
+	go readADC(a1, 17*time.Millisecond, 1)
+	go readADC(a2, 29*time.Millisecond, 2)
+
+	for {
+		fmt.Printf("ADC0: %5d ADC1: %5d ADC2: %5d Temp: %v\n\r", adcReading[0], adcReading[1], adcReading[2], celsius(float32(t.ReadTemperature())/1000))
+		time.Sleep(1000 * time.Millisecond)
+	}
+}

src/machine/machine_rp2040_adc.go

@@ -5,58 +5,142 @@ package machine
 
 import (
 	"device/rp"
+	"errors"
+	"sync"
 )
 
+// ADCChannel is the ADC peripheral mux channel. 0-4.
+type ADCChannel uint8
+
+// ADC channels. Only ADC_TEMP_SENSOR is public. The other channels are accessed via Machine.ADC objects
+const (
+	adc0_CH ADCChannel = iota
+	adc1_CH
+	adc2_CH
+	adc3_CH         // Note: GPIO29 not broken out on pico board
+	ADC_TEMP_SENSOR // Internal temperature sensor channel
+)
+
+// Used to serialise ADC sampling
+var adcLock sync.Mutex
+
+// ADC peripheral reference voltage (mV)
+var adcAref uint32
+
+// InitADC resets the ADC peripheral.
 func InitADC() {
-	// reset ADC
 	rp.RESETS.RESET.SetBits(rp.RESETS_RESET_ADC)
 	rp.RESETS.RESET.ClearBits(rp.RESETS_RESET_ADC)
 	for !rp.RESETS.RESET_DONE.HasBits(rp.RESETS_RESET_ADC) {
 	}
-
 	// enable ADC
 	rp.ADC.CS.Set(rp.ADC_CS_EN)
-
+	adcAref = 3300
 	waitForReady()
 }
 
-// Configure configures a ADC pin to be able to be used to read data.
-func (a ADC) Configure(config ADCConfig) {
+// Configure sets the ADC pin to analog input mode.
+func (a ADC) Configure(config ADCConfig) error {
+	c, err := a.GetADCChannel()
+	if err != nil {
+		return err
+	}
+	return c.Configure(config)
+}
+
+// Get returns a one-shot ADC sample reading.
+func (a ADC) Get() uint16 {
+	if c, err := a.GetADCChannel(); err == nil {
+		return c.getOnce()
+	}
+	// Not an ADC pin!
+	return 0
+}
+
+// GetADCChannel returns the channel associated with the ADC pin.
+func (a ADC) GetADCChannel() (c ADCChannel, err error) {
+	err = nil
 	switch a.Pin {
-	case ADC0, ADC1, ADC2, ADC3:
-		a.Pin.Configure(PinConfig{Mode: PinAnalog})
+	case ADC0:
+		c = adc0_CH
+	case ADC1:
+		c = adc1_CH
+	case ADC2:
+		c = adc2_CH
+	case ADC3:
+		c = adc3_CH
 	default:
-		// invalid ADC
-		return
+		err = errors.New("no ADC channel for pin value")
 	}
+	return c, err
 }
 
-func (a ADC) Get() uint16 {
-	rp.ADC.CS.SetBits(uint32(a.getADCChannel()) << rp.ADC_CS_AINSEL_Pos)
+// Configure sets the channel's associated pin to analog input mode or powers on the temperature sensor for ADC_TEMP_SENSOR.
+// The powered on temperature sensor increases ADC_AVDD current by approximately 40 μA.
+func (c ADCChannel) Configure(config ADCConfig) error {
+	if config.Reference != 0 {
+		adcAref = config.Reference
+	}
+	if p, err := c.Pin(); err == nil {
+		p.Configure(PinConfig{Mode: PinAnalog})
+	}
+	if c == ADC_TEMP_SENSOR {
+		// Enable temperature sensor bias source
+		rp.ADC.CS.SetBits(rp.ADC_CS_TS_EN)
+	}
+	return nil
+}
+
+// getOnce returns a one-shot ADC sample reading from an ADC channel.
+func (c ADCChannel) getOnce() uint16 {
+	// Make it safe to sample multiple ADC channels in separate go routines.
+	adcLock.Lock()
+	rp.ADC.CS.ReplaceBits(uint32(c), 0b111, rp.ADC_CS_AINSEL_Pos)
 	rp.ADC.CS.SetBits(rp.ADC_CS_START_ONCE)
 
 	waitForReady()
+	adcLock.Unlock()
+
+	// rp2040 is a 12-bit ADC, scale raw reading to 16-bits.
+	return uint16(rp.ADC.RESULT.Get()) << 4
+}
 
-	// rp2040 uses 12-bit sampling, so scale to 16-bit
-	return uint16(rp.ADC.RESULT.Get() << 4)
+// getVoltage does a one-shot sample and returns a millivolts reading.
+// Integer portion is stored in the high 16 bits and fractional in the low 16 bits.
+func (c ADCChannel) getVoltage() uint32 {
+	return (adcAref << 16) / (1 << 12) * uint32(c.getOnce()>>4)
 }
 
+// ReadTemperature does a one-shot sample of the internal temperature sensor and returns a milli-celsius reading.
+// Only works on the ADC_TEMP_SENSOR channel. aka AINSEL=4. Other channels will return 0
+func (c ADCChannel) ReadTemperature() (millicelsius uint32) {
+	if c != ADC_TEMP_SENSOR {
+		return
+	}
+	// T = 27 - (ADC_voltage - 0.706)/0.001721
+	return (27000<<16 - (c.getVoltage()-706<<16)*581) >> 16
+}
+
+// waitForReady spins waiting for the ADC peripheral to become ready.
 func waitForReady() {
 	for !rp.ADC.CS.HasBits(rp.ADC_CS_READY) {
 	}
 }
 
-func (a ADC) getADCChannel() uint8 {
-	switch a.Pin {
-	case ADC0:
-		return 0
-	case ADC1:
-		return 1
-	case ADC2:
-		return 2
-	case ADC3:
-		return 3
+// The Pin method returns the GPIO Pin associated with the ADC mux channel, if it has one.
+func (c ADCChannel) Pin() (p Pin, err error) {
+	err = nil
+	switch c {
+	case adc0_CH:
+		p = ADC0
+	case adc1_CH:
+		p = ADC1
+	case adc2_CH:
+		p = ADC2
+	case adc3_CH:
+		p = ADC3
 	default:
-		return 0
+		err = errors.New("no associated pin for channel")
 	}
+	return p, err
 }