spi: incorporate change from GH issue feedback

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

apa102/apa102.go

@@ -29,14 +29,6 @@ type Device struct {
 	Order int
 }
 
-// The SPI interface specifies the minimum functionality that a bus
-// implementation needs to provide for use by the APA102 driver.  Hardware
-// SPI from the TinyGo "machine" package implements this already.
-// type SPI interface {
-// 	Tx(w, r []byte) error
-// 	Transfer(b byte) (byte, error)
-// }
-
 // New returns a new APA102 driver. Pass in a fully configured SPI bus.
 func New(b drivers.SPI) Device {
 	return Device{bus: b, Order: BGR}

spi.go

@@ -2,6 +2,12 @@ package drivers
 
 // SPI represents a SPI bus. It is implemented by the machine.SPI type.
 type SPI interface {
+	// Tx transmits the given buffer w and receives at the same time the buffer r.
+	// The two buffers must be the same length. The only exception is when w or r are nil,
+	// in which case Tx only transmits (without receiving) or only receives (while sending 0 bytes).
 	Tx(w, r []byte) error
+
+	// Transfer writes a single byte out on the SPI bus and receives a byte at the same time.
+	// If you want to transfer multiple bytes, it is more efficient to use Tx instead.
 	Transfer(b byte) (byte, error)
 }

wifinina/wifinina.go

@@ -269,7 +269,7 @@ type Device struct {
 	ssids [10]string
 }
 
-// New returns a new Wiifinina driver.
+// New returns a new Wifinina driver.
 func New(bus drivers.SPI, csPin, ackPin, gpio0Pin, resetPin machine.Pin) *Device {
 	return &Device{
 		SPI:   bus,