spi: correct support for MCP3004/MCP3008 A/D converters

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

drivers/spi/README.MD

@@ -14,6 +14,9 @@ Gobot has a extensible system for connecting to hardware devices.
 
 The following spi Devices are currently supported:
 
+- APA102 Programmable LEDs
+- MCP3004 Analog/Digital Converter
+- MCP3008 Analog/Digital Converter
 - GoPiGo3 Robot
 
 Drivers wanted! :)

drivers/spi/mcp3004.go

@@ -1,11 +1,15 @@
 package spi
 
 import (
+	"errors"
 	"strconv"
 
 	"gobot.io/x/gobot"
 )
 
+// MCP3004DriverMaxChannel is the number of channels (plus one) of this A/D converter.
+const MCP3004DriverMaxChannel = 3
+
 // MCP3004Driver is a driver for the MCP3008 A/D converter.
 type MCP3004Driver struct {
 	name       string
@@ -54,15 +58,24 @@ func (d *MCP3004Driver) Halt() (err error) {
 }
 
 // Read reads the current analog data for the desired channel.
-func (d *MCP3004Driver) Read(channel int) (int, error) {
+func (d *MCP3004Driver) Read(channel int) (result int, err error) {
+	if channel < 0 || channel > MCP3004DriverMaxChannel {
+		return 0, errors.New("Invalid channel for read")
+	}
+
 	tx := make([]byte, 3)
 	tx[0] = 0x01
 	tx[1] = 0x80 + (byte(channel) << 4)
 	tx[2] = 0x00
 
-	d.connection.Tx(tx, nil)
+	rx := make([]byte, 3)
 
-	return 0, nil
+	err = d.connection.Tx(tx, rx)
+	if err == nil && len(rx) == 3 {
+		result = int(((rx[1] & 0x03) << 8) + rx[2])
+	}
+
+	return result, err
 }
 
 // AnalogRead returns value from analog reading of specified pin

drivers/spi/mcp3004_test.go

@@ -32,4 +32,6 @@ func TestMCP3004DriverHalt(t *testing.T) {
 func TestMCP3004DriverRead(t *testing.T) {
 	d := initTestMCP3004Driver()
 	d.Start()
+
+	// TODO: actual read test
 }

drivers/spi/mcp3008.go

@@ -1,11 +1,15 @@
 package spi
 
 import (
+	"errors"
 	"strconv"
 
 	"gobot.io/x/gobot"
 )
 
+// MCP3008DriverMaxChannel is the number of channels (plus one) of this A/D converter.
+const MCP3008DriverMaxChannel = 7
+
 // MCP3008Driver is a driver for the MCP3008 A/D converter.
 type MCP3008Driver struct {
 	name       string
@@ -54,15 +58,24 @@ func (d *MCP3008Driver) Halt() (err error) {
 }
 
 // Read reads the current analog data for the desired channel.
-func (d *MCP3008Driver) Read(channel int) (int, error) {
+func (d *MCP3008Driver) Read(channel int) (result int, err error) {
+	if channel < 0 || channel > MCP3008DriverMaxChannel {
+		return 0, errors.New("Invalid channel for read")
+	}
+
 	tx := make([]byte, 3)
 	tx[0] = 0x01
 	tx[1] = 0x80 + (byte(channel) << 4)
 	tx[2] = 0x00
 
-	d.connection.Tx(tx, nil)
+	rx := make([]byte, 3)
 
-	return 0, nil
+	err = d.connection.Tx(tx, rx)
+	if err == nil && len(rx) == 3 {
+		result = int(((rx[1] & 0x03) << 8) + rx[2])
+	}
+
+	return result, err
 }
 
 // AnalogRead returns value from analog reading of specified pin

drivers/spi/mcp3008_test.go

@@ -32,4 +32,6 @@ func TestMCP3008DriverHalt(t *testing.T) {
 func TestMCP3008DriverRead(t *testing.T) {
 	d := initTestMCP3008Driver()
 	d.Start()
+
+	// TODO: actual read test
 }