Add basic support for INA219 current sensor

CONTRIBUTORS

@@ -6,3 +6,4 @@ Nikesh Vora <nikesh.voratp@gmail.com>
 Steve Beaulac <steve@beaulac.me>
 Al S-M <asm@rndm.io>
 Ben Delarre <ben@delarre.net>
+Cullen Jennings <fluffy@cisco.com>

samples/.gitignore

@@ -8,6 +8,7 @@ gpio
 gpiodetect
 gpiodirect
 gpioshort
+ina219
 l3gd20
 led
 ledshort

samples/ina219.go

@@ -0,0 +1,49 @@
+// +build ignore
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"time"
+
+	"github.com/kidoman/embd"
+	"github.com/kidoman/embd/sensor/ina219"
+
+	_ "github.com/kidoman/embd/host/all"
+)
+
+func main() {
+	flag.Parse()
+
+	if err := embd.InitI2C(); err != nil {
+		panic(err)
+	}
+	defer embd.CloseI2C()
+
+	bus := embd.NewI2CBus(1)
+
+	ina := ina219.New(bus, 0x40, 0.1)
+	defer ina.Close()
+
+	for {
+		sv, err := ina.ShuntVoltage()
+		if err != nil {
+			panic(err)
+		}
+
+		v, err := ina.Voltage()
+		if err != nil {
+			panic(err)
+		}
+
+		c, err := ina.Current()
+		if err != nil {
+			panic(err)
+		}
+
+		fmt.Printf("Shunt Voltage=%v  Voltage=%v Current=%v\n", sv, v, c)
+
+		time.Sleep(500 * time.Millisecond)
+	}
+}

sensor/ina219/ina219.go

@@ -0,0 +1,131 @@
+// Package ina219 allows interfacing with Texas Instruments INA219 current
+// monitor. This is a high side current and voltage monitor with and I2C
+// interfcace.
+
+// TODO - add options to config voltage range, sensitivity and averaging
+
+package ina219
+
+import (
+	"math"
+	"sync"
+
+	"github.com/golang/glog"
+	"github.com/kidoman/embd"
+)
+
+const (
+	configReg  = 0x00
+	shuntVReg  = 0x01
+	busVReg    = 0x02
+	powerReg   = 0x03
+	currentReg = 0x04
+	calibReg   = 0x05
+)
+
+// INA219 represents a Bosch INA219 current sensor.
+type INA219 struct {
+	Bus embd.I2CBus
+
+	address        byte
+	shuntResitance float64
+
+	initialized bool
+	mu          sync.RWMutex
+}
+
+func New(bus embd.I2CBus, addr byte, shunt float64) *INA219 {
+	ina := INA219{
+		Bus:            bus,
+		address:        addr,
+		shuntResitance: shunt,
+	}
+	return &ina
+}
+
+func (d *INA219) setup() error {
+	d.mu.RLock()
+	if d.initialized {
+		d.mu.RUnlock()
+		return nil
+	}
+	d.mu.RUnlock()
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	config := uint16(0x219F) // 12, bit no integration, 32v bus range , 40mV shunt range
+	err := d.Bus.WriteWordToReg(d.address, configReg, config)
+	if err != nil {
+		return err
+	}
+
+	calib := uint16(0.5 + 40.96/d.shuntResitance)
+
+	err = d.Bus.WriteWordToReg(d.address, calibReg, calib) // .1 ohm sense resitor
+	if err != nil {
+		return err
+	}
+
+	glog.V(1).Infof("ina219: initaliized")
+
+	d.initialized = true
+
+	return nil
+}
+
+func (d *INA219) ShuntVoltage() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, shuntVReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	voltage := float64(v) / 100000.0
+
+	return voltage, nil
+}
+
+func (d *INA219) Voltage() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, busVReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	voltage := float64(v>>3) / 250.0
+
+	return voltage, nil
+}
+
+func (d *INA219) Current() (float64, error) {
+	if err := d.setup(); err != nil {
+		return math.NaN(), err
+	}
+
+	v, err := d.Bus.ReadWordFromReg(d.address, currentReg)
+	if err != nil {
+		return math.NaN(), err
+	}
+
+	current := float64(v) / 1000.0
+
+	return current, nil
+}
+
+// Close
+func (d *INA219) Close() error {
+	// put in power down mode
+	config := uint16(0x0000)
+	err := d.Bus.WriteWordToReg(d.address, configReg, config)
+	if err != nil {
+		return err
+	}
+	return nil
+}