machine/stm32f4: initial implementation for ADC interface

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

src/machine/machine_stm32_adc.go

@@ -0,0 +1,115 @@
+//go:build stm32f4
+// +build stm32f4
+
+package machine
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+// InitADC initializes the registers needed for ADC1.
+func InitADC() {
+	// Enable ADC clock
+	enableAltFuncClock(unsafe.Pointer(stm32.ADC1))
+
+	// stop scan, and clear scan resolution
+	stm32.ADC1.CR1.ClearBits(stm32.ADC_CR1_SCAN | stm32.ADC_CR1_RES_Msk)
+
+	// set conversion mode and resolution
+	stm32.ADC1.CR1.SetBits(stm32.ADC_CR1_RES_TwelveBit)
+
+	// clear CONT, ALIGN, EXTEN and EXTSEL bits from CR2
+	stm32.ADC1.CR2.ClearBits(stm32.ADC_CR2_CONT | stm32.ADC_CR2_ALIGN | stm32.ADC_CR2_EXTEN_Msk | stm32.ADC_CR2_EXTSEL_Msk)
+
+	// set CONT, ALIGN, EXTEN and EXTSEL bits from CR2
+	stm32.ADC1.CR2.SetBits(stm32.ADC_CR2_CONT_Single | stm32.ADC_CR2_ALIGN_Right)
+
+	stm32.ADC1.SQR1.ClearBits(stm32.ADC_SQR1_L_Msk)
+	stm32.ADC1.SQR1.SetBits(2 << stm32.ADC_SQR1_L_Pos) // 2 means 3 conversions
+
+	// enable
+	stm32.ADC1.CR2.SetBits(stm32.ADC_CR2_ADON)
+
+	return
+}
+
+// Configure configures an ADC pin to be able to read analog data.
+func (a ADC) Configure(ADCConfig) {
+	a.Pin.ConfigureAltFunc(PinConfig{Mode: PinInputAnalog}, 0)
+
+	// set sample time
+	ch := a.getChannel()
+	if ch > 9 {
+		stm32.ADC1.SMPR1.SetBits(stm32.ADC_SMPR1_SMP11_Cycles84 << (ch - 10) * stm32.ADC_SMPR1_SMP11_Pos)
+	} else {
+		stm32.ADC1.SMPR2.SetBits(stm32.ADC_SMPR2_SMP1_Cycles84 << (ch * stm32.ADC_SMPR2_SMP1_Pos))
+	}
+
+	return
+}
+
+// Get returns the current value of a ADC pin in the range 0..0xffff.
+// TODO: DMA based implementation.
+func (a ADC) Get() uint16 {
+	// set rank
+	ch := uint32(a.getChannel())
+	stm32.ADC1.SQR3.SetBits(ch)
+
+	// start conversion
+	stm32.ADC1.CR2.SetBits(stm32.ADC_CR2_SWSTART)
+
+	// wait for conversion to complete
+	for !stm32.ADC1.SR.HasBits(stm32.ADC_SR_EOC) {
+	}
+
+	// read 12-bit result as 16 bit value
+	result := uint16(stm32.ADC1.DR.Get()) << 4
+
+	// clear flag
+	stm32.ADC1.SR.ClearBits(stm32.ADC_SR_EOC)
+
+	// clear rank
+	stm32.ADC1.SMPR1.ClearBits(ch)
+
+	return result
+}
+
+func (a ADC) getChannel() uint8 {
+	switch a.Pin {
+	case PA0:
+		return 0
+	case PA1:
+		return 1
+	case PA2:
+		return 2
+	case PA3:
+		return 3
+	case PA4:
+		return 4
+	case PA5:
+		return 5
+	case PA6:
+		return 6
+	case PA7:
+		return 7
+	case PB0:
+		return 8
+	case PB1:
+		return 9
+	case PC0:
+		return 10
+	case PC1:
+		return 11
+	case PC2:
+		return 12
+	case PC3:
+		return 13
+	case PC4:
+		return 14
+	case PC5:
+		return 15
+	}
+
+	return 0
+}

src/machine/machine_stm32_moder_gpio.go

@@ -143,6 +143,10 @@ func (p Pin) ConfigureAltFunc(config PinConfig, altFunc uint8) {
 		port.OSPEEDR.ReplaceBits(gpioOutputSpeedHigh, gpioOutputSpeedMask, pos)
 		port.PUPDR.ReplaceBits(gpioPullFloating, gpioPullMask, pos)
 		p.SetAltFunc(altFunc)
+
+	// ADC
+	case PinInputAnalog:
+		port.MODER.ReplaceBits(gpioModeAnalog, gpioModeMask, pos)
 	}
 }