machine/nrf: SPI master implementation

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

src/examples/mcp3008/mcp3008.go

@@ -0,0 +1,55 @@
+// Connects to an MCP3008 ADC via SPI.
+// Datasheet: https://www.microchip.com/wwwproducts/en/en010530
+package main
+
+import (
+	"errors"
+	"machine"
+	"time"
+)
+
+// CS_PIN is the pin used for Chip Select (CS). Change to whatever is in use on your board.
+const CS_PIN = 3
+
+var (
+	tx          []byte
+	rx          []byte
+	val, result uint16
+	cs          machine.GPIO
+)
+
+func main() {
+	cs = machine.GPIO{CS_PIN}
+	cs.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+
+	machine.SPI0.Configure(machine.SPIConfig{
+		Frequency: 4000000,
+		Mode:      3})
+
+	tx = make([]byte, 3)
+	rx = make([]byte, 3)
+
+	for {
+		val, _ = Read(0)
+		println(val)
+		time.Sleep(50 * time.Millisecond)
+	}
+}
+
+// Read analog data from channel
+func Read(channel int) (uint16, error) {
+	if channel < 0 || channel > 7 {
+		return 0, errors.New("Invalid channel for read")
+	}
+
+	tx[0] = 0x01
+	tx[1] = byte(8+channel) << 4
+	tx[2] = 0x00
+
+	cs.Low()
+	machine.SPI0.Tx(tx, rx)
+	result = uint16((rx[1]&0x3))<<8 + uint16(rx[2])
+	cs.High()
+
+	return result, nil
+}

src/machine/board_microbit.go

@@ -36,6 +36,13 @@ const (
 	SCL_PIN = 0  // P19 on the board
 )
 
+// SPI pins
+const (
+	SPI0_SCK_PIN  = 0
+	SPI0_MOSI_PIN = 0
+	SPI0_MISO_PIN = 0
+)
+
 // LED matrix pins
 const (
 	LED_COL_1 = 4

src/machine/board_nrf52840-mdk.go

@@ -23,3 +23,10 @@ const (
 	SDA_PIN = 0xff
 	SCL_PIN = 0xff
 )
+
+// SPI pins (unused)
+const (
+	SPI0_SCK_PIN  = 0
+	SPI0_MOSI_PIN = 0
+	SPI0_MISO_PIN = 0
+)

src/machine/board_pca10031.go

@@ -30,3 +30,10 @@ const (
 	SDA_PIN = 0xff
 	SCL_PIN = 0xff
 )
+
+// SPI pins (unused)
+const (
+	SPI0_SCK_PIN  = 0
+	SPI0_MOSI_PIN = 0
+	SPI0_MISO_PIN = 0
+)

src/machine/board_pca10040.go

@@ -44,3 +44,10 @@ const (
 	SDA_PIN = 26
 	SCL_PIN = 27
 )
+
+// SPI pins
+const (
+	SPI0_SCK_PIN  = 25
+	SPI0_MOSI_PIN = 23
+	SPI0_MISO_PIN = 24
+)

src/machine/board_pca10056.go

@@ -30,6 +30,13 @@ const (
 
 // I2C pins
 const (
-	SDA_PIN = 26
-	SCL_PIN = 27
+	SDA_PIN = 26 // P0.26
+	SCL_PIN = 27 // P0.27
+)
+
+// SPI pins
+const (
+	SPI0_SCK_PIN  = 47 // P1.15
+	SPI0_MOSI_PIN = 45 // P1.13
+	SPI0_MISO_PIN = 46 // P1.14
 )

src/machine/board_reelboard.go

@@ -33,3 +33,10 @@ const (
 	SDA_PIN = 26
 	SCL_PIN = 27
 )
+
+// SPI pins
+const (
+	SPI0_SCK_PIN  = 47
+	SPI0_MOSI_PIN = 45
+	SPI0_MISO_PIN = 46
+)

src/machine/machine_nrf.go

@@ -232,3 +232,98 @@ func (i2c I2C) readLastByte() byte {
 	i2c.signalStop() // signal 'stop' now, so it is sent when reading RXD
 	return byte(i2c.Bus.RXD)
 }
+
+// SPI on the NRF.
+type SPI struct {
+	Bus *nrf.SPI_Type
+}
+
+// There are 2 SPI interfaces on the NRF5x.
+var (
+	SPI0 = SPI{Bus: nrf.SPI0}
+	SPI1 = SPI{Bus: nrf.SPI1}
+)
+
+// SPIConfig is used to store config info for SPI.
+type SPIConfig struct {
+	Frequency uint32
+	SCK       uint8
+	MOSI      uint8
+	MISO      uint8
+	LSBFirst  bool
+	Mode      uint8
+}
+
+// Configure is intended to setup the SPI interface.
+func (spi SPI) Configure(config SPIConfig) {
+	// Disable bus to configure it
+	spi.Bus.ENABLE = nrf.SPI_ENABLE_ENABLE_Disabled
+
+	// set frequency
+	var freq uint32
+
+	switch config.Frequency {
+	case 125000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_K125
+	case 250000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_K250
+	case 500000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_K500
+	case 1000000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_M1
+	case 2000000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_M2
+	case 4000000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_M4
+	case 8000000:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_M8
+	default:
+		freq = nrf.SPI_FREQUENCY_FREQUENCY_K500
+	}
+	spi.Bus.FREQUENCY = nrf.RegValue(freq)
+
+	var conf uint32
+
+	// set bit transfer order
+	if config.LSBFirst {
+		conf = (nrf.SPI_CONFIG_ORDER_LsbFirst << nrf.SPI_CONFIG_ORDER_Pos)
+	}
+
+	// set mode
+	switch config.Mode {
+	case 0:
+		conf &^= (nrf.SPI_CONFIG_CPOL_ActiveHigh << nrf.SPI_CONFIG_CPOL_Pos)
+		conf &^= (nrf.SPI_CONFIG_CPHA_Leading << nrf.SPI_CONFIG_CPHA_Pos)
+	case 1:
+		conf &^= (nrf.SPI_CONFIG_CPOL_ActiveHigh << nrf.SPI_CONFIG_CPOL_Pos)
+		conf |= (nrf.SPI_CONFIG_CPHA_Trailing << nrf.SPI_CONFIG_CPHA_Pos)
+	case 2:
+		conf |= (nrf.SPI_CONFIG_CPOL_ActiveLow << nrf.SPI_CONFIG_CPOL_Pos)
+		conf &^= (nrf.SPI_CONFIG_CPHA_Leading << nrf.SPI_CONFIG_CPHA_Pos)
+	case 3:
+		conf |= (nrf.SPI_CONFIG_CPOL_ActiveLow << nrf.SPI_CONFIG_CPOL_Pos)
+		conf |= (nrf.SPI_CONFIG_CPHA_Trailing << nrf.SPI_CONFIG_CPHA_Pos)
+	default: // to mode
+		conf &^= (nrf.SPI_CONFIG_CPOL_ActiveHigh << nrf.SPI_CONFIG_CPOL_Pos)
+		conf &^= (nrf.SPI_CONFIG_CPHA_Leading << nrf.SPI_CONFIG_CPHA_Pos)
+	}
+	spi.Bus.CONFIG = nrf.RegValue(conf)
+
+	// set pins
+	spi.setPins(config.SCK, config.MOSI, config.MISO)
+
+	// Re-enable bus now that it is configured.
+	spi.Bus.ENABLE = nrf.SPI_ENABLE_ENABLE_Enabled
+}
+
+// Transfer writes/reads a single byte using the SPI interface.
+func (spi SPI) Transfer(w byte) (byte, error) {
+	spi.Bus.TXD = nrf.RegValue(w)
+	for spi.Bus.EVENTS_READY == 0 {
+	}
+	r := spi.Bus.RXD
+	spi.Bus.EVENTS_READY = 0
+
+	// TODO: handle SPI errors
+	return byte(r), nil
+}

src/machine/machine_nrf51.go

@@ -25,3 +25,19 @@ func (i2c I2C) setPins(scl, sda uint8) {
 	i2c.Bus.PSELSCL = nrf.RegValue(scl)
 	i2c.Bus.PSELSDA = nrf.RegValue(sda)
 }
+
+// SPI
+func (spi SPI) setPins(sck, mosi, miso uint8) {
+	if sck == 0 {
+		sck = SPI0_SCK_PIN
+	}
+	if mosi == 0 {
+		mosi = SPI0_MOSI_PIN
+	}
+	if miso == 0 {
+		miso = SPI0_MISO_PIN
+	}
+	spi.Bus.PSELSCK = nrf.RegValue(sck)
+	spi.Bus.PSELMOSI = nrf.RegValue(mosi)
+	spi.Bus.PSELMISO = nrf.RegValue(miso)
+}

src/machine/machine_nrf52.go

@@ -27,6 +27,22 @@ func (i2c I2C) setPins(scl, sda uint8) {
 	i2c.Bus.PSELSDA = nrf.RegValue(sda)
 }
 
+// SPI
+func (spi SPI) setPins(sck, mosi, miso uint8) {
+	if sck == 0 {
+		sck = SPI0_SCK_PIN
+	}
+	if mosi == 0 {
+		mosi = SPI0_MOSI_PIN
+	}
+	if miso == 0 {
+		miso = SPI0_MISO_PIN
+	}
+	spi.Bus.PSEL.SCK = nrf.RegValue(sck)
+	spi.Bus.PSEL.MOSI = nrf.RegValue(mosi)
+	spi.Bus.PSEL.MISO = nrf.RegValue(miso)
+}
+
 // InitADC initializes the registers needed for ADC.
 func InitADC() {
 	return // no specific setup on nrf52 machine.

src/machine/machine_nrf52840.go

@@ -29,3 +29,19 @@ func (i2c I2C) setPins(scl, sda uint8) {
 	i2c.Bus.PSEL.SCL = nrf.RegValue(scl)
 	i2c.Bus.PSEL.SDA = nrf.RegValue(sda)
 }
+
+// SPI
+func (spi SPI) setPins(sck, mosi, miso uint8) {
+	if sck == 0 {
+		sck = SPI0_SCK_PIN
+	}
+	if mosi == 0 {
+		mosi = SPI0_MOSI_PIN
+	}
+	if miso == 0 {
+		miso = SPI0_MISO_PIN
+	}
+	spi.Bus.PSEL.SCK = nrf.RegValue(sck)
+	spi.Bus.PSEL.MOSI = nrf.RegValue(mosi)
+	spi.Bus.PSEL.MISO = nrf.RegValue(miso)
+}

src/machine/spi.go

@@ -0,0 +1,70 @@
+// +build nrf
+
+package machine
+
+import "errors"
+
+var (
+	ErrTxSlicesRequired   = errors.New("SPI Tx requires a write or read slice, or both")
+	ErrTxInvalidSliceSize = errors.New("SPI write and read slices must be same size")
+)
+
+// Tx handles read/write operation for SPI interface. Since SPI is a syncronous write/read
+// interface, there must always be the same number of bytes written as bytes read.
+// The Tx method knows about this, and offers a few different ways of calling it.
+//
+// This form sends the bytes in tx buffer, putting the resulting bytes read into the rx buffer.
+// Note that the tx and rx buffers must be the same size:
+//
+// 		spi.Tx(tx, rx)
+//
+// This form sends the tx buffer, ignoring the result. Useful for sending "commands" that return zeros
+// until all the bytes in the command packet have been received:
+//
+// 		spi.Tx(tx, nil)
+//
+// This form sends zeros, putting the result into the rx buffer. Good for reading a "result packet":
+//
+// 		spi.Tx(nil, rx)
+//
+func (spi SPI) Tx(w, r []byte) error {
+	if w == nil && r == nil {
+		return ErrTxSlicesRequired
+	}
+
+	var err error
+
+	switch {
+	case w == nil:
+		// read only, so write zero and read a result.
+		for i := range r {
+			r[i], err = spi.Transfer(0)
+			if err != nil {
+				return err
+			}
+		}
+	case r == nil:
+		// write only
+		for _, b := range w {
+			_, err = spi.Transfer(b)
+			if err != nil {
+				return err
+			}
+		}
+
+	default:
+		// write/read
+		if len(w) != len(r) {
+			return ErrTxInvalidSliceSize
+		}
+
+		for i, b := range w {
+			r[i], err = spi.Transfer(b)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}