How to use SPI

Overview

This How-To is meant to be a starting point for people to learn use SPI for IGEP devices as quickly and easily as possible. In this how-to, we run an example program that reads and writes registers from 3-axis accelerometer (LIS3DH) included on the board IGEP New York.

Requirements

There are some requisites to follow this guide:

IGEP SDK VM: follow the IGEP SDK SOFTWARE USER MANUAL (chapter 2.3 "Setting up and running the VM")
IGEP Firmware: follow the IGEP SDK SOFTWARE USER MANUAL (chapter 6.1 "Create IGEP firmware bootable micro-sd card")
IGEP COM MODULE and IGEP NEW YORK
SPI example program
MicroSD Card (at least 2Gbytes)

How Works

LIS3DH accelerometer: It is the accelerometer mounted in IGEP New York.

Omap3 SPI Peripheral: It is the hardware used to communicated with accelerometer and other SPI devices.

Omap2_mcspi: It is a bus driver than controls Omap3 SPI Peripheral.

Spi: It is a protocol driver that defines functions and strucs used in SPI bus.

Spidev: It is a device driver that export spi driver functionalities to userspace.

Lis3lv02d_spi: SPI glue layer for lis3lv02d

Lis31v02d: Device driver for LIS3DH accelerometer.

Exp_ilms0015: It is a startup program for IGEP New York. It attach lis31v02d with Spi driver.

More information about Linux Kernel SPI at:

SPI Overview

SPIDEV

Prepare Micro SD Card

Generate Micro SD Card

Open a terminal and use the following steps to download and generate a Micro SD card.

wget http://downloads.isee.biz/denzil/binary/igep_firmware-yocto-1.2.1-1.tar.bz2 
tar jxf igep_firmware-yocto-*.tar.bz2
cd igep_firmware-yocto-*

Insert a SD-Card and use the igep-media-create script to copy the firmware.

./igep-media-create -–mmc <mmc> --image demo-image-sato-igep00x0.tar.bz2 --machine igep0030

where <mmc> - is the SD-Card device of your computer. For example, assuming the SD-card device takes '/dev/sdb' type:

./igep-media-create --mmc /dev/sdb --machine igep0030 --image demo-image-sato-igep00x0.tar.bz2

This should give you a bootable SD-card with IGEP COM MODULE support.

Custom Micro SD Card

Get Linux kernel sources

We will get from git repository the kernel sources:

Clone the Kernel git repository

jdoe@ubuntu ~ $ git clone git://git.igep.es/pub/scm/linux-omap-2.6.git
jdoe@ubuntu ~ $ cd linux-omap-2.6/

Checkout your desired branch (we used for this howto 2.6.37.y)

jdoe@ubuntu ~/linux-omap-2.6 $ git checkout origin/linux-2.6.37.y -b linux-2-6-37.y

Modify Linux Kernel Sources to attach Spidev to SPI driver

To read accelerometer registers from spidev, we need to attach spidev driver to spi driver at start up. So it is necessary to modify spi_board.

Go to $(Kernel path)/arch/arm/mach-omap2/exp-ilms0015.c and edit the next fields in bold words.

static struct spi_board_info lis3lv02d_spi_board_info __initdata = {

.modalias = "spidev",

//.modalias = "lis3lv02d_spi",

.bus_num = -EINVAL,

.chip_select = -EINVAL,

.max_speed_hz = 1*1000*1000,

.irq = -EINVAL,

.mode = SPI_MODE_0,

//.platform_data = &lis3lv02d_pdata,

};

inline void __init ilms0015_lis3lv02d_init(int bus_num, int cs, int irq)

{

struct spi_board_info *spi = &lis3lv02d_spi_board_info;

if ((gpio_request(irq, "LIS3LV02D IRQ") == 0)

&& (gpio_direction_input(irq) == 0))

gpio_export(irq, 0);

else {

pr_err("IGEP: Could not obtain gpio LIS3LV02D IRQ\n");

return;

}

spi->bus_num = bus_num;

spi->chip_select = cs;

spi->irq = OMAP_GPIO_IRQ(irq),

spi_register_board_info(&lis3lv02d_spi_board_info, 1);

}

...

void __init ilms0015_init(void)

{

mux_partition = omap_mux_get("core");

/* Mux initialitzation for ilms0015 */

omap_mux_write_array(mux_partition, ilms0015_mux);

/* 3-axis accelerometer */

ilms0015_lis3lv02d_init(1, 2, 174);

/* Export some GPIO */

ilms0015_gpio_init();

}

Now spi_register_board_info has all information necessary to attach spidev driver instead lis3lv02d_spi.

Compile Kernel

Export IGEP SDK sources

jdoe@ubuntu ~ $ source /opt/poky/1.2/environment-setup-armv7a-vfp-neon-poky-linux-gnueabi

Configure the kernel

jdoe@ubuntu ~ $ cd linux-omap-2.6/
jdoe@ubuntu ~/linux-omap-2.6 $  make ARCH=arm CROSS_COMPILE=arm-poky-linux-gnueabi- igep00x0_defconfig

Build the kernel and Modules

jdoe@ubuntu ~/linux-omap-2.6 $  make ARCH=arm CROSS_COMPILE=arm-poky-linux-gnueabi- zImage modules

Copy Kernel to SD card

Kernel binary resides inside the directory:$(Kernel path)/arch/arm/boot/zImage. Copy binary to SD boot partition:

jdoe@ubuntu ~/linux-omap-2.6 $ mv arch/arm/boot/zImage /media/boot/zImage

Copy Kernel modules:

jdoe@ubuntu ~/linux-omap-2.6 $ sudo make ARCH=arm modules_install INSTALL_MOD_PATH=/media/rootfs

Enable ilms0015 support

By default, igep-media-create ,configured as igep0030, gives support only for IGEP Expansions Paris and Berlin. We need to configure igep.ini (located at boot partition) and gives support to IGEP New York:

; Machine configuration

;buddy=base0010 buddy.revision=B

buddy=ilms0015

NOTE: “ilms0015” is the technical name of IGEP New York.

Test changes

Once you copy your new Kernel binaries and edit igep.ini:

Power up your board with your new SD card
Enable removable device: RNDIS/Ethernet Gadget
Set up usb0 network device:

jdoe@ubuntu ~ $ sudo ifup usb0 
jdoe@ubuntu ~ $ ifconfig usb0
usb0      Link encap:Ethernet  HWaddr 32:3a:b0:bc:cc:15  
          inet addr:192.168.7.10  Bcast:192.168.7.255  Mask:255.255.255.0
          inet6 addr: fe80::303a:b0ff:febc:cc15/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:53 errors:0 dropped:0 overruns:0 frame:0
          TX packets:46 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:10584 (10.5 KB)  TX bytes:9203 (9.2 KB)

jdoe@ubuntu ~ $

Log in:

jdoe@ubuntu ~ $ ssh root@192.168.7.1
root@igep00x0:~#

Check your changes (spidev will be enabled):

root@igep00x0:~# lsmod
Module                  Size  Used by
ip_tables               9402  0 
rfcomm                 48492  0 
hidp                   13271  0 
l2cap                  48548  4 rfcomm,hidp
bluetooth              67154  3 rfcomm,hidp,l2cap
option                 13048  0 
usb_wwan                7163  1 option
libertas_sdio          13919  0 
twl4030_wdt             2623  0 
spidev                  4906  0 
libertas               98995  1 libertas_sdio
omap_wdt                3171  0 
usbserial              23882  2 option,usb_wwan
root@igep00x0:~#

“spidev1.2”: refers at McSPI1 bus 2. Now we can communicate to accelerometer using spi driver functions.

SPI Test program

Overview

This program is based in spidev_test and it was edited to run with LIS3DH accelerometer. Program can be explained in four parts:

Connection properties: program lets change via parameters SPI configurations like: device, max speed, delay, bits per word, clock phase, clock polarity, etc. If you don't use any of this parameters program will use default options for LIS3DH communication.

Read mode: Reads a word from a register.

Write mode: Writes a word in a register.

Test mode: Reads X, Y and Z axes from accelerometer.

We recommend to read peripheral datasheet before use or modify program.

Compile program

The program source was compiled with Yocto SDK but you can use other compilers like Linaro Toolchain:

source /opt/poky/1.2/environment-setup-armv7a-vfp-neon-poky-linux-gnueabi
arm-poky-linux-gnueabi-gcc spiexamplebeta2.c -o spiexampleb2

Copy your final binary to rootfs.

Test program

Read WHO_AM_I register(0Fh)

LIS3DH has this dummy register (See 8.6 chapter) as a device identification. Its value is 0x33:

root@igep00x0:~# ./spiexampleb2 -R 0F 
spi mode: 0 
bits per word: 8 
max speed: 1000000 Hz (1000 KHz) 
Value from 0F is: 33 
root@igep00x0:~#

Read and Write CTRL_REG1 (20h)

This register is used to enable/disable: accelerometer and XYZ axes (See 8.8 chapter). The default value at startup is:

root@igep00x0:~# ./spiexampleb2 -R 20 
spi mode: 0 
bits per word: 8 
max speed: 1000000 Hz (1000 KHz) 
Value from 20 is: 07 
root@igep00x0:~#

It means that accelerometer was disabled and X, Y and Z axes was enabled. For example we can disable X axe typing:

root@igep00x0:~# ./spiexampleb2 -W 20 -V 06 
spi mode: 0 
bits per word: 8 
max speed: 1000000 Hz (1000 KHz) 
Register to write 20 with value 06 
root@igep00x0:~# ./spiexampleb2 -R 20      
spi mode: 0 
bits per word: 8 
max speed: 1000000 Hz (1000 KHz) 
Value from 20 is: 06 
root@igep00x0:~#

Read accelerometer axes

Finally we are going to read gravity force: LIS3DH has ±2g/±4g/±8g/±16g dynamically selectable full scale (See chapter 8.11). The axes values are expressed in two’s complement in 16 bits (See chapters 8.16, 8.17 and 8.18).

root@igep00x0:~# ./spiexampleb2 -T 
spi mode: 0 
bits per word: 8 
max speed: 1000000 Hz (1000 KHz) 
Accelerometer TEST 
Values from X -64, Values from Y -15872 and Values from Z -256 
root@igep00x0:~#

The next table shows results at different positions:

Position

±2g scale

±4g scale

±8g scale

±16g scale

X = 832

Y = 1024

Z = 15680

X = 256

Y = 128

Z = 7872

X = 128

Y = 128

Z = 4032

X = 64

Y = 128

Z = 1280

X = 256

Y = 704

Z = -17216

X = 256

Y = 256

Z = -8320

X = 64

Y = 128

Z = -4096

X = 128

Y = 128

Z = -1344

X = -15872

Y = 64

Z = -320

X = -7936

Y = 64

Z = -512

X = -3968

Y = 128

Z = -192

X = -1280

Y = 64

Z = -128

X = 16448

Y = 640

Z = 640

X = 8128

Y = 192

Z = 384

X = 4032

Y = 64

Z = 64

X = 1344

Y = 64

Z = 192

X = 896

Y = 16512

Z = -576

X = 320

Y = 8128

Z = -128

X = 192

Y = 4096

Z = -64

X = 128

Y = 1344

Z = -128

X = -64

Y = -15872

Z = -256

X = -512

Y = -7808

Z = -384

X = -64

>Y = -3840

Z = -384

X = -128

Y = -1216

Z = -128

Personal tools

Search

Namespaces

Views

Export pages

Actions

How to use SPI

From IGEP - ISEE Wiki

Contents

Overview

Requirements

How Works

Prepare Micro SD Card

Generate Micro SD Card

Custom Micro SD Card

Get Linux kernel sources

Modify Linux Kernel Sources to attach Spidev to SPI driver

Compile Kernel

Copy Kernel to SD card

Enable ilms0015 support

Test changes

SPI Test program

Overview

Compile program

Test program

Read WHO_AM_I register(0Fh)

Read and Write CTRL_REG1 (20h)

Read accelerometer axes

Navigation menu

External Links

Special pages