Linux kernel space

AN4503

16/26

DocID026411 Rev 2

3.3

Permission setting

The permission of some files in the ramdisk.img should be specifically set by adding some

lines to the relevant init.<board>.rc file (for the Panda-board, the file

init.omap4pandabpard.rc located in <RAS>/device/ti/panda).

In particular:

chmod 0666 /sys/class/input/input<x>/device/device/enable_device

chown system system /sys/class/input/input<x>/device/device/enable_device

chmod 0666 /sys/class/input/input<x>/device/device/full_scale

chown system system /sys/class/input/input<x>/device/device/full_scale

chmod 0666 /sys/class/input/input<x>/device/device/poll_period_ms

chown system system /sys/class/input/input<x>/device/device/poll_period_ms

where <x> is the 'number' corresponding to the proper event.

After modifying the above mentioned file, run "make bootimage" from <RAS> to build the

new boot.img. This new image, which includes the kernel (zImage in <KR>/arch/arm/boot)

and the ramdisk.img, can be found in <RAS>/device/ti/panda.

3.4

Output data from the driver

3.4.1

Where to find the data

The Linux infrastructure provides the raw data from the driver in the assigned

/dev/input/event<x> devices (see the routine <device>_report_values, where <device> is

the name of the device, hts221 or lps25h or uvis).

This data can be accessed with the corresponding command from the Linux shell

 [Android shell]$ getevent /dev/input/event<x>

The real values (read from the device or calculated) can also be read as real values via the

Minicom for debugging purposes only. Do this by enabling #DEBUG in the corresponding

driver and then read the data through pr_info in hts221_get_data() or

lps25_prs_get_presstemp_data().

3.4.2

Sample application for reading data

The data exported in /dev/event/input<X> can also be read with a simple algorithm in the C

language, in a dynamic library or directly from an application.

Below is a simple skeleton, where argv[1] is the path: /dev/input/event

#include <stdio.h>

#include <time.h>

#include <sys/times.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <unistd.h>

#include <stdint.h>

#include <assert.h>