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LED usage on DVEVM

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This article describes the usage of the 8 user controlled LEDs on DM6446 DVEVM.


On DM6446 DVEVM there are 8 user controllable LEDs available. These are controlled using I2C device PCF 8574A (I2C address 0x38).

See page 27 of TMS320DM6446 EVM schematic and section 2.4 (page 2-7) of Davinci-DM644x EVM Technical Reference.


In MontaVisata Linux kernel and recent git kernel device driver to control LEDs is located in


It controls four LEDs:

  • "red" -> DS1
  • "amber" -> DS2
  • "green" -> DS3
  • "blue" -> DS4

Note: Actually, all LEDs on DM6446 DVEVM are green :) But ARMs LED framework defines only these four colors. This seems to be the reason why only four of the 8 possible LEDs are controlled using this framework.

LED at DS8 is defined as "timer LED" and can be controlled by kernel configuration option CONFIG_LEDS_TIMER.

Note: CONFIG_LEDS_TIMER can only be set if CONFIG_GENERIC_CLOCKEVENTS is not set. Therefore this option isn't available in default DM6446 DVEVM git kernel configuration.


The 8 user controlled LEDs can be switched by user space software or by device drivers.

User space

From user space, you can control the four above LEDs via sysfs:

> echo claim > /sys/devices/system/leds/leds0/event
> echo green on > /sys/devices/system/leds/leds0/event
> echo red on > /sys/devices/system/leds/leds0/event
> echo red off > /sys/devices/system/leds/leds0/event
> echo amber on > /sys/devices/system/leds/leds0/event
> echo blue on > /sys/devices/system/leds/leds0/event
> echo release > /sys/devices/system/leds/leds0/event

Note: the release turns off the LED's!

Example program

* Eric Tanner 2007.
* Simple program to blink the LEDs on the DaVinci
* EVM using the the LED port expander PCF8574A at I2C Slave Address 0x38.
* I2C Support and I2C device interface must be turned on in the kernel. 

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <signal.h>
#define I2C_DEVICE      "/dev/i2c/0"
#define I2C_DEV_ADDR    0x38
#define I2C_SLAVE       0x0703

int main()
       int i2c_fd;
       int state = 0;
       unsigned char val = 0x00;
       int ret;

       struct timespec req = {
               .tv_sec = 0,
               .tv_nsec = 100000000,

       if((i2c_fd = open(I2C_DEVICE,O_RDWR)) < 0) {
               printf("Unable to open the i2c port!\n");

       if(ioctl(i2c_fd, I2C_SLAVE, I2C_DEV_ADDR)== -1) {
               close( i2c_fd );
               printf("Unable to setup the i2c port!\n");

       do {
               val <<= 1;
               val |= 0x01;
               if(val == 0xFF)
                       val = 0xFE;
               write( i2c_fd, &val, 1);

        } while (!nanosleep (&req, NULL));

       close ( i2c_fd );
       printf ("End.\n");
       return 0;

Device drivers

Device drivers can use function call



#include <asm/leds.h>