Texas Instruments OPT3001EVM Manuale utente

OPT3001EVM Linux Getting Started Guide

Felipe Balbi

August 18, 2014

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Contents

1 Scope 1

2 Introduction 2

2.1 OPT3001 ............................... 2

2.2 BeagleBoneBlack .......................... 2

2.3 LinuxKernel ............................. 2

3 Hardware Platform 3

4 The Linux Kernel 5

4.1 Writing Our DeviceTree . . . . . . . . . . . . . . . . . . . . . . . 5

4.2 Downloading The Correct Version . . . . . . . . . . . . . . . . . 6

4.3 Kernel Conﬁguration . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Usage 13

6 Conclusion 15

Chapter 1

Scope

This document will describe the necessary steps to connect OPT3001EVM to

a BeagleBone Black development platform.

By the end of this User’s Guide, the reader should be able to verify function-

ality of the OPT3001 device and get results from light measurements.

Chapter 2

Introduction

2.1 OPT3001

The OPT3001 is an ideal sensing device for measuring ambient light. Mea-

surements can be made from 0.01 lux up to 83k lux without selecting full-scale

ranges by using the built-in, full-scale setting feature. This capability allows

light measurement over a 23-bit eﬀective dynamic range.

The spectral response of the ambient light sensor is tightly matched to the

photopic response of the human eye and has signiﬁcant infrared rejection. This

tightly matched response oﬀers accurate lux readings of diﬀerent spectral sources,

even under dark glass.

The digital operation is ﬂexible for system integration. Measurements can

be either continuous or single-shot. The control and interrupt system features

autonomous operation, allowing the processor to sleep while the sensor searches

for appropriate wake-up events.

The low power consumption and low power-supply voltage capability make

this device ideal for battery-powered applications.

2.2 Beagle Bone Black

Beagle Bone Black is an Open Source Hardware Software Development Plat-

form using Texas Instruments’ AM335x System-on-Chip device.

It provides an easy to use Software Development Platform based on an ARM

Cortex-A8 CPU together with many other peripherals integrated into the die.

2.3 Linux Kernel

The Linux Kernel was created by Linus Torvalds back in 1991. It’s a General

Purpose Operating System which works in many diﬀerent architectures includ-

ing, but not limited to, x86, ARM, ARC, Power, MIPS, and Alpha.

Chapter 3

Hardware Platform

For the purpose of this Getting Started Guide, we will be using OPT3001EVM

Rev B and Beagle Bone Black Rev A5C.

The picture below shows a simple way of connecting OPT3001EVM to the

Beagle Bone Black using a standard 100 mil spacing breadboard.

Connected like that, OPT3001 will show on Beagle Bone Black’s I2C Bus 2

1. The following section will describe all the necessary steps to get OPT3001

working on our Beagle Bone Black.

1note that I2C Bus numbers start at 0, so I2C Bus 2 is the third I2C Bus on Beagle Bone

Black

CHAPTER 3. HARDWARE PLATFORM 4

Figure 3.1: connecting opt3001evm to beagle bone black

Chapter 4

The Linux Kernel

4.1 Writing Our DeviceTree

Now that we have OPT3001EVM connected to our Beagle Bone Black, we

need to tell Linux about it. Recent Linux Kernel release utilize Open Firmware

as the methodology for ﬁrmware to tell the Operating System about devices

which sit under non-enumerable buses. The language used by Open ﬁrmware is

known as DeviceTree

With a DeviceTree source such as below, we can tell Linux that we have

an OPT3001 device sitting under I2C Bus 2 and can be accessed through I2C

address 0x44.

/* arch/arm/boot/dts/am335x-boneblack.dts */

&i2c2 {

status = "okay";

pinctrl-names = "default";

pinctrl-0 = <&i2c2_pins>;

clock-frequency = <400000>;

light@44 {

status = "okay";

pinctrl-names = "default";

pinctrl-0 = <&light_pins>;

compatible = "opt3001";

reg = <0x44>;

interrupts-extended = <&gpio1 28 IRQ_TYPE_LEVEL_HIGH>;

};

Note that we have two undeﬁned pinctrl DeviceTree nodes. Let’s deﬁne them:

/* arch/arm/boot/dts/am335x-boneblack.dts */

CHAPTER 4. THE LINUX KERNEL 6

&am33xx_pinmux {

i2c2_pins: i2c2_pins {

pinctrl-single,pins = <

0x178 (PIN_INPUT | SLEWCTRL_FAST | MUX_MODE3) /*

uart1_ctsn.i2c2_sda */

0x17c (PIN_INPUT | SLEWCTRL_FAST | MUX_MODE3) /*

uart1_rtsn.i2c2_scl */

};

light_pins: light_pins {

pinctrl-single,pins = <

0x78 (PIN_INPUT | MUX_MODE7) /* gpmc_ben1.gpio1_28

};

4.2 Downloading The Correct Version

At the time of this writing OPT3001 driver is still not merged in the Mainline

1Linux Kernel tree. Because of that we have provided git branches for all Linux

Kernel versions starting with v3.14 all the way to v3.17.

On each of those branches, you will ﬁnd the same OPT3001 driver together

with Beagle Bone Black devicetree changes for easy start.

Depending on which Linux Kernel version you’re using, download the correct

branch as per table below:

Linux Version GIT URL

v3.14 git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git opt3001-v3.14

v3.15 git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git opt3001-v3.15

v3.16 git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git opt3001-v3.16

v3.17 git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git opt3001-v3.17

To download any of those branches a certain level of knowledge about the git

version control system is required but the short version is below 2.

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git

linux

cloning into ’linux’...

remote: counting objects: 3802743, done.

remote: compressing objects: 100% (582455/582455), done.

remote: total 3802743 (delta 3207582), reused 3785375 (delta 3190275)

receiving objects: 100% (3802743/3802743), 801.20 mib | 1.84 mib/s, done.

resolving deltas: 100% (3207582/3207582), done.

1Linux Kernel tree maintained by Linus Torvalds

2we are assuming the reader already has git installed in their system

CHAPTER 4. THE LINUX KERNEL 7

checking connectivity... done.

checking out files: 100% (47441/47441), done.

$cd linux

$ git reset --hard opt3001-v3.14

4.3 Kernel Conﬁguration

After downloading the Kernel sources, we need to conﬁgure it for our setup.

We will start by running:

$ make ARCH=arm CROSS_COMPILE=arm-linux- omap2plus_defconfig

hostcc scripts/basic/fixdep

hostcc scripts/kconfig/conf.o

shipped scripts/kconfig/zconf.tab.c

shipped scripts/kconfig/zconf.lex.c

shipped scripts/kconfig/zconf.hash.c

hostcc scripts/kconfig/zconf.tab.o

hostld scripts/kconfig/conf

# configuration written to .config

This ﬁrst command will select all common conﬁguration for Texas Instru-

ments’ SoCs, including AM335x. Now we need to enable OPT3001 driver. For

that, we will run:

$ make arch=arm cross_compile=arm-linux- menuconfig

You should see a screen such as below in Figure 4.1.

After that, let’s enable the industrial i/o framework and opt3001 driver, please

follow the steps below and refer to the Screen Captures, if necessary.

1. navigate to Device Drivers and press ENTER (see ﬁgure 4.2);

2. navigate to Industrial I/O support (see ﬁgure 4.3);

(a) press M3(see ﬁgure 4.4); or

(b) press Y4(see ﬁgure 4.5);

3. navigate to Light sensors and press ENTER (see ﬁgure 4.6);

4. navigate to Texas Instruments OPT3001 Light Sensor (see ﬁgure 4.7);

(a) press M(see ﬁgure 4.8); or

(b) press Y(see ﬁgure 4.9);

3M will compile a dynamically linked module

4Y will link the binary statically to the kernel image

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