More on Leds

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As mentioned in Controlling LEDs from the Shell, there are some sysfs endpoints for controlling the LEDs. For a small example of a native program twiddling the LEDs using these endpoints, check out:

Just copy the program to your Palm Pre, and then:

gunzip leds_demo.gz
chmod u+x leds_demo

The LEDS are controlled by a low power special-purpose LED driver IC, the LP8501. It's controlled by the i2c bus. It allows preset programs to do things like fade-ins and fade-outs without requiring CPU intervention. I'm investigating it more, stay tuned.

Since the source is short, I'll post it right here:

#include "stdio.h"
#include "math.h"

int main(int argc, char** argv) {

    int i = 0, val = 0, phase1=120, phase2=240, s=1000;
    FILE *left_led, *right_led, *center_led; 
    char buf[10];
    float PI = 3.14159;

    if(argc < 4) {
        puts("Usage: leds_demo delay(us) led2_offset led3_offset");
        puts("Phase is in degrees around a circle. 120, 240 for perfect spacing");
        puts("I.E.: leds_demo 1000 120 240");
        puts("This example will be run now");
    } else {
        s = atoi(argv[1]);
        phase1 = atoi(argv[2]);
        phase2 = atoi(argv[3]);
    left_led =  fopen("/sys/class/leds/core_navi_left/brightness", "w");
    right_led =  fopen("/sys/class/leds/core_navi_right/brightness", "w");
    center_led =  fopen("/sys/class/leds/core_navi_center/brightness", "w");
    while(1) {
        val = sin(i*2*PI/360.0)*32+32;
        sprintf(buf, "%d\n", val); 
        fwrite(buf, strlen(buf), 1, left_led);

        val = sin((i+phase1)*2*PI/360.0)*32+32;
        sprintf(buf, "%d\n", val); 
        fwrite(buf, strlen(buf), 1, center_led);
        val = sin((i+phase2)*2*PI/360.0)*32+32;
        sprintf(buf, "%d\n", val); 
        fwrite(buf, strlen(buf), 1, right_led);