machine: redesign I2C interface

src/machine/i2c.go

@@ -7,3 +7,26 @@ const (
 	TWI_FREQ_100KHZ = 100000
 	TWI_FREQ_400KHZ = 400000
 )
+
+// WriteRegister transmits first the register and then the data to the
+// peripheral device.
+//
+// Many I2C-compatible devices are organized in terms of registers. This method
+// is a shortcut to easily write to such registers. Also, it only works for
+// devices with 7-bit addresses, which is the vast majority.
+func (i2c I2C) WriteRegister(address uint8, register uint8, data []byte) error {
+	buf := make([]uint8, len(data)+1)
+	buf[0] = register
+	copy(buf[1:], data)
+	return i2c.Tx(uint16(address), buf, nil)
+}
+
+// ReadRegister transmits the register, restarts the connection as a read
+// operation, and reads the response.
+//
+// Many I2C-compatible devices are organized in terms of registers. This method
+// is a shortcut to easily read such registers. Also, it only works for devices
+// with 7-bit addresses, which is the vast majority.
+func (i2c I2C) ReadRegister(address uint8, register uint8, data []byte) error {
+	return i2c.Tx(uint16(address), []byte{register}, data)
+}