feat(src/machine/nrf52xxx/spi): add SPI mode type

Signed-off-by: Paul Schroeder <milkpirate@users.noreply.github.com>

Author: milkpirate

src/machine/machine_nrf52xxx.go

@@ -8,6 +8,41 @@ import (
 	"unsafe"
 )
 
+const (
+	SPI_CPHA0_CPOL0 SPIMode = iota
+	SPI_CPHA1_CPOL0
+	SPI_CPHA1_CPOL1
+	SPI_CPHA0_CPOL1
+)
+
+// There are 3 SPI interfaces on the NRF528xx.
+var (
+	SPI0 = SPI{Bus: nrf.SPIM0}
+	SPI1 = SPI{Bus: nrf.SPIM1}
+	SPI2 = SPI{Bus: nrf.SPIM2}
+)
+
+type SPIMode uint8
+
+func (m *SPIMode) ApplyTo(conf uint32) uint32 {
+	// see https://de.wikipedia.org/wiki/Serial_Peripheral_Interface#/media/Datei:SPI_timing_diagram2.svg
+	switch m {
+	case SPI_CPHA1_CPOL0:
+		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
+		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
+	case SPI_CPHA1_CPOL1:
+		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
+		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
+	case SPI_CPHA0_CPOL1:
+		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
+		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
+	case SPI_CPHA0_CPOL0:
+		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
+		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
+	}
+	return conf
+}
+
 func CPUFrequency() uint32 {
 	return 64000000
 }
@@ -185,7 +220,7 @@ type SPIConfig struct {
 	SDO       Pin
 	SDI       Pin
 	LSBFirst  bool
-	Mode      uint8
+	Mode      SPIMode
 }
 
 // Configure is intended to setup the SPI interface.
@@ -226,23 +261,7 @@ func (spi SPI) Configure(config SPIConfig) error {
 	}
 
 	// set mode
-	switch config.Mode {
-	case 0:
-		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
-		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
-	case 1:
-		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
-		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
-	case 2:
-		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
-		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
-	case 3:
-		conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
-		conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
-	default: // to mode
-		conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
-		conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
-	}
+	conf = config.Mode.Apply(conf)
 	spi.Bus.CONFIG.Set(conf)
 
 	// set pins