mpu9250: Add i2c interface support (#101)

* Refactor SPI transport to be dual transport. 
* Implement I2C support.

Author: gsexton

mpu9250/mpu9250.go

@@ -2,7 +2,12 @@
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
-// Package mpu9250 MPU-9250 is a 9-axis MotionTracking device that combines a 3-axis gyroscope, 3-axis accelerometer, 3-axis magnetometer and a Digital Motion Processor™ (DMP)
+// Package mpu9250 MPU-9250 is a 9-axis MotionTracking device that combines a
+// 3-axis gyroscope, 3-axis accelerometer, 3-axis magnetometer and a Digital
+// Motion Processor™ (DMP). Connections via SPI or I2C are supported.
+//
+// There is a sample program in periph.io/x/cmd/mpu9250 that you can run to
+// test using the sensor.
 //
 // # Datasheet
 //
@@ -24,16 +29,6 @@ const (
 	accelsenSitivity = 16384
 )
 
-// Proto defines the low-level methods used by different transports.
-type Proto interface {
-	writeMaskedReg(address byte, mask byte, value byte) error
-	readMaskedReg(address byte, mask byte) (byte, error)
-	readByte(address byte) (byte, error)
-	writeByte(address byte, value byte) error
-	readUint16(address ...byte) (uint16, error)
-	writeMagReg(address byte, value byte) error
-}
-
 // AccelerometerData the values for x/y/z axises.
 type AccelerometerData struct {
 	X, Y, Z int16
@@ -62,14 +57,14 @@ type SelfTestResult struct {
 
 // MPU9250 defines the structure to keep reference to the transport.
 type MPU9250 struct {
-	transport Proto
+	transport Transport
 	debug     func(string, ...interface{})
 }
 
 // New creates the new instance of the driver.
 //
 // transport the transport interface.
-func New(transport Proto) (*MPU9250, error) {
+func New(transport Transport) (*MPU9250, error) {
 	return &MPU9250{transport: transport, debug: noop}, nil
 }
 

mpu9250/spi.go

@@ -0,0 +1,148 @@
+// Copyright 2020 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package mpu9250
+
+import (
+	"fmt"
+
+	"periph.io/x/conn/v3/gpio"
+	"periph.io/x/conn/v3/i2c"
+	"periph.io/x/conn/v3/physic"
+	"periph.io/x/conn/v3/spi"
+	"periph.io/x/conn/v3/spi/spireg"
+)
+
+// DebugF the debug function type.
+type DebugF func(string, ...interface{})
+
+// Transport Encapsulates the SPI transport parameters.
+type Transport struct {
+	device spi.Conn
+	d      *i2c.Dev
+	cs     gpio.PinOut
+	debug  DebugF
+}
+
+// NewSpiTransport Creates the SPI transport using the provided device path and chip select pin reference.
+func NewSpiTransport(path string, cs gpio.PinOut) (*Transport, error) {
+	dev, err := spireg.Open(path)
+	if err != nil {
+		return nil, wrapf("can't open SPI %v", err)
+	}
+	conn, err := dev.Connect(1*physic.MegaHertz, spi.Mode0, 8)
+	if err != nil {
+		return nil, wrapf("can't initialize SPI %v", err)
+	}
+	return &Transport{device: conn, cs: cs, debug: noop}, nil
+}
+
+func NewI2cTransport(bus i2c.Bus, address uint16) (*Transport, error) {
+	return &Transport{d: &i2c.Dev{Bus: bus, Addr: address}, debug: noop}, nil
+}
+
+// EnableDebug Sets the debugging output using the local print function.
+func (t *Transport) EnableDebug(f DebugF) {
+	t.debug = f
+}
+
+func (t *Transport) writeByte(address byte, value byte) error {
+	if t.d == nil {
+		return t.writeByteSPI(address, value)
+	}
+	return t.writeByteI2C(address, value)
+}
+
+func (t *Transport) writeByteSPI(address, value byte) error {
+	t.debug("write register %x value %x", address, value)
+	var (
+		buf = [...]byte{address, value}
+		res [2]byte
+	)
+	if err := t.cs.Out(gpio.Low); err != nil {
+		return err
+	}
+	if err := t.device.Tx(buf[:], res[:]); err != nil {
+		return err
+	}
+	return t.cs.Out(gpio.High)
+}
+
+func (t *Transport) writeByteI2C(address, value byte) error {
+	w := []byte{address, value}
+	return t.d.Tx(w, nil)
+}
+
+func (t *Transport) writeMaskedReg(address byte, mask byte, value byte) error {
+	t.debug("write masked %x, mask %x, value %x", address, mask, value)
+	maskedValue := mask & value
+	t.debug("masked value %x", maskedValue)
+	regVal, err := t.readByte(address)
+	if err != nil {
+		return err
+	}
+	t.debug("current register %x", regVal)
+	regVal = (regVal &^ maskedValue) | maskedValue
+	t.debug("new value %x", regVal)
+	return t.writeByte(address, regVal)
+}
+
+func (t *Transport) readMaskedReg(address byte, mask byte) (byte, error) {
+	t.debug("read masked %x, mask %x", address, mask)
+	reg, err := t.readByte(address)
+	if err != nil {
+		return 0, err
+	}
+	t.debug("masked value %x", reg)
+	return reg & mask, nil
+}
+
+func (t *Transport) readByte(address byte) (byte, error) {
+	if t.d == nil {
+		return t.readByteSPI(address)
+	}
+	return t.readByteI2C(address)
+}
+
+func (t *Transport) readByteSPI(address byte) (byte, error) {
+	t.debug("read register %x", address)
+	var (
+		buf = [...]byte{0x80 | address, 0}
+		res [2]byte
+	)
+	if err := t.cs.Out(gpio.Low); err != nil {
+		return 0, err
+	}
+	if err := t.device.Tx(buf[:], res[:]); err != nil {
+		return 0, err
+	}
+	t.debug("register content %x:%x", res[0], res[1])
+	if err := t.cs.Out(gpio.High); err != nil {
+		return 0, err
+	}
+	return res[1], nil
+}
+
+func (t *Transport) readByteI2C(address byte) (byte, error) {
+	r := make([]byte, 1)
+	err := t.d.Tx([]byte{address}, r)
+	return r[0], err
+}
+
+func (t *Transport) readUint16(address ...byte) (uint16, error) {
+	if len(address) != 2 {
+		return 0, fmt.Errorf("only 2 bytes per read")
+	}
+	h, err := t.readByte(address[0])
+	if err != nil {
+		return 0, err
+	}
+	l, err := t.readByte(address[1])
+	if err != nil {
+		return 0, err
+	}
+	return uint16(h)<<8 | uint16(l), nil
+}
+
+func noop(string, ...interface{}) {}