Add support samd5x's SPI 32-bit extension

Author: sago35

src/machine/machine_atsamd51.go

@@ -1241,6 +1241,9 @@ func (spi SPI) Configure(config SPIConfig) error {
 		spi.Bus.CTRLA.ClearBits(sam.SERCOM_SPIM_CTRLA_CPOL)
 	}
 
+	// 32bit
+	spi.Bus.CTRLC.SetBits(sam.SERCOM_SPIM_CTRLC_DATA32B)
+
 	// Set synch speed for SPI
 	baudRate := SERCOM_FREQ_REF / (2 * config.Frequency)
 	spi.Bus.BAUD.Set(uint8(baudRate))
@@ -1256,6 +1259,7 @@ func (spi SPI) Configure(config SPIConfig) error {
 // Transfer writes/reads a single byte using the SPI interface.
 func (spi SPI) Transfer(w byte) (byte, error) {
 	// write data
+	spi.Bus.LENGTH.Set(sam.SERCOM_SPIM_LENGTH_LENEN | 1)
 	spi.Bus.DATA.Set(uint32(w))
 
 	// wait for receive
@@ -1266,6 +1270,34 @@ func (spi SPI) Transfer(w byte) (byte, error) {
 	return byte(spi.Bus.DATA.Get()), nil
 }
 
+// Transfer2 writes/reads a single uint16 using the SPI interface.
+func (spi SPI) Transfer2(w uint16) (uint16, error) {
+	// write data
+	spi.Bus.LENGTH.Set(sam.SERCOM_SPIM_LENGTH_LENEN | 2)
+	spi.Bus.DATA.Set(uint32(w))
+
+	// wait for receive
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+	}
+
+	// return data
+	return uint16(spi.Bus.DATA.Get()), nil
+}
+
+// Transfer4 writes/reads a single uint32 using the SPI interface.
+func (spi SPI) Transfer4(w uint32) (uint32, error) {
+	// write data
+	spi.Bus.LENGTH.Set(sam.SERCOM_SPIM_LENGTH_LENEN | 4)
+	spi.Bus.DATA.Set(w)
+
+	// wait for receive
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+	}
+
+	// return data
+	return spi.Bus.DATA.Get(), nil
+}
+
 // The QSPI peripheral on ATSAMD51 is only available on the following pins
 const (
 	QSPI_SCK   = PB10