machine/rp2040: add basic support for ADC

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/board_pico.go

@@ -38,6 +38,12 @@ const (
 	// Onboard LED
 	LED Pin = GP25
 
+	// Analog pins
+	ADC0 = GP26
+	ADC1 = GP27
+	ADC2 = GP28
+	ADC3 = GP29
+
 	// Onboard crystal oscillator frequency, in MHz.
 	xoscFreq = 12 // MHz
 )

src/machine/machine_rp2040_adc.go

@@ -0,0 +1,61 @@
+// +build rp2040
+
+package machine
+
+import (
+	"device/rp"
+)
+
+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)
+
+	waitForReady()
+}
+
+// Configure configures a ADC pin to be able to be used to read data.
+func (a ADC) Configure(config ADCConfig) {
+	switch a.Pin {
+	case GP26, GP27, GP28, GP29:
+		a.Pin.Configure(PinConfig{Mode: PinAnalog})
+	default:
+		// invalid ADC
+		return
+	}
+}
+
+func (a ADC) Get() uint16 {
+	rp.ADC.CS.SetBits(uint32(a.getADCChannel()) << rp.ADC_CS_AINSEL_Pos)
+	rp.ADC.CS.SetBits(rp.ADC_CS_START_ONCE)
+
+	waitForReady()
+
+	// rp2040 uses 12-bit sampling, so scale to 16-bit
+	return uint16(rp.ADC.RESULT.Get() << 4)
+}
+
+func waitForReady() {
+	for !rp.ADC.CS.HasBits(rp.ADC_CS_READY) {
+	}
+}
+
+func (a ADC) getADCChannel() uint8 {
+	switch a.Pin {
+	case GP26:
+		return 0
+	case GP27:
+		return 1
+	case GP28:
+		return 2
+	case GP29:
+		return 3
+	default:
+		return 0
+	}
+}

src/machine/machine_rp2040_gpio.go

@@ -66,6 +66,7 @@ const (
 	PinInput
 	PinInputPulldown
 	PinInputPullup
+	PinAnalog
 )
 
 // set drives the pin high
@@ -109,6 +110,11 @@ func (p Pin) pulldown() {
 	p.padCtrl().ClearBits(rp.PADS_BANK0_GPIO0_PUE)
 }
 
+func (p Pin) pulloff() {
+	p.padCtrl().ClearBits(rp.PADS_BANK0_GPIO0_PDE)
+	p.padCtrl().ClearBits(rp.PADS_BANK0_GPIO0_PUE)
+}
+
 // setFunc will set pin function to fn.
 func (p Pin) setFunc(fn pinFunc) {
 	// Set input enable, Clear output disable
@@ -125,7 +131,6 @@ func (p Pin) init() {
 	mask := uint32(1) << p
 	rp.SIO.GPIO_OE_CLR.Set(mask)
 	p.clr()
-	p.setFunc(fnSIO)
 }
 
 // Configure configures the gpio pin as per mode.
@@ -134,15 +139,19 @@ func (p Pin) Configure(config PinConfig) {
 	mask := uint32(1) << p
 	switch config.Mode {
 	case PinOutput:
+		p.setFunc(fnSIO)
 		rp.SIO.GPIO_OE_SET.Set(mask)
 	case PinInput:
-		rp.SIO.GPIO_OE_CLR.Set(mask)
+		p.setFunc(fnSIO)
 	case PinInputPulldown:
-		rp.SIO.GPIO_OE_CLR.Set(mask)
+		p.setFunc(fnSIO)
 		p.pulldown()
 	case PinInputPullup:
-		rp.SIO.GPIO_OE_CLR.Set(mask)
+		p.setFunc(fnSIO)
 		p.pullup()
+	case PinAnalog:
+		p.setFunc(fnNULL)
+		p.pulloff()
 	}
 }