周六的中午还是依旧来了公司,本来也没有打算来的,既然来了,那就把上次遗留下来的一些问题给解决吧,把android下的pwm调lcd背光给总结下吧。关于android的背光,是用pwm波来控制的,通过占空比的不同,得到不同的电压值,从而点亮的lcd的亮度就不同了。具体的也就是控制了电压值而已。
要在android上层搞定背光的调节,那么必须准备底层驱动了,首先就是那个backlight了,这个linux驱动的模型已经做好了,只要选上就ok了。
Device下的graphics support
选上那个backlight就好了
还有要准备相应平台的pwm的驱动,准备好这些后,就ok了。然后跑一下就会生成一个节点:
- /sys/class/backlight/pwm-backlight/brightness
只要
- echo 100 > /sys/class/backlight/pwm-backlight/brightness
- echo 50 > /sys/class/backlight/pwm-backlight/brightness
如果背光改变了,那么就说明驱动OK了,也可以用示波器看pwm引脚,是否有变换。
如果不成功,那么就继续调试底层驱动吧。接着就是要上android了。
对于背光,android代码中主要是:
- Frameworks/base/services/jni/com_android_server_LightsService.cpp
- Frameworks/base/services/java/com/android/server/LightsServer.java
这里就不用太去关注了,移植到android主要就是硬件抽象层的事情了,java层会调用jni层,jni层会调到相应的硬件抽象层,硬件抽象层再继续调用底层驱动。好了,还是看看lcd背光的硬件抽象层吧。
对于不同平台那个lights.c是放在不同地方的,比如你的是samsung的tuna平台,那么就
在/device/Samsung/tuna/liblights/lights.c下。
- #define LOG_TAG "lights"
- #include <cutils/log.h>
- #include <stdint.h>
- #include <string.h>
- #include <errno.h>
- #include <fcntl.h>
- #include <pthread.h>
- #include <sys/ioctl.h>
- #include <sys/types.h>
- #include <hardware/lights.h>
- #include <linux/leds-an30259a.h>
- static pthread_once_t g_init = PTHREAD_ONCE_INIT;
- static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;
- char const *const LCD_FILE = "/sys/class/backlight/s6e8aa0/brightness";
- char const *const LED_FILE = "/dev/an30259a_leds";
- #define IMAX 0 // 12.75mA power consumption
- // Slope values, based on total blink of 1000ms
- #define SLOPE_UP_1 450
- #define SLOPE_UP_2 (500-SLOPE_UP_1)
- #define SLOPE_DOWN_1 SLOPE_UP_2
- #define SLOPE_DOWN_2 SLOPE_UP_1
- // brightness at mid-slope, on 0 - 127 scale
- #define MID_BRIGHTNESS 31
- void init_g_lock(void)
- {
- pthread_mutex_init(&g_lock, NULL);
- }
- static int write_int(char const *path, int value)
- {
- int fd;
- static int already_warned;
- already_warned = 0;
- LOGV("write_int: path %s, value %d", path, value);
- fd = open(path, O_RDWR);
- if (fd >= 0) {
- char buffer[20];
- int bytes = sprintf(buffer, "%d\n", value);
- int amt = write(fd, buffer, bytes);
- close(fd);
- return amt == -1 ? -errno : 0;
- } else {
- if (already_warned == 0) {
- LOGE("write_int failed to open %s\n", path);
- already_warned = 1;
- }
- return -errno;
- }
- }
- static int rgb_to_brightness(struct light_state_t const *state)
- {
- int color = state->color & 0x00ffffff;
- return ((77*((color>>16) & 0x00ff))
- + (150*((color>>8) & 0x00ff)) + (29*(color & 0x00ff))) >> 8;
- }
- static int set_light_backlight(struct light_device_t *dev,
- struct light_state_t const *state)
- {
- int err = 0;
- int brightness = rgb_to_brightness(state);
- pthread_mutex_lock(&g_lock);
- err = write_int(LCD_FILE, brightness);
- pthread_mutex_unlock(&g_lock);
- return err;
- }
- static int close_lights(struct light_device_t *dev)
- {
- LOGV("close_light is called");
- if (dev)
- free(dev);
- return 0;
- }
- /* LEDs */
- static int write_leds(struct an30259a_pr_control *led)
- {
- int err = 0;
- int imax = IMAX;
- int fd;
- pthread_mutex_lock(&g_lock);
- fd = open(LED_FILE, O_RDWR);
- if (fd >= 0) {
- err = ioctl(fd, AN30259A_PR_SET_IMAX, &imax);
- if (err)
- LOGE("failed to set imax");
- err = ioctl(fd, AN30259A_PR_SET_LED, led);
- if (err < 0)
- LOGE("failed to set leds!");
- close(fd);
- } else {
- LOGE("failed to open %s!", LED_FILE);
- err = -errno;
- }
- pthread_mutex_unlock(&g_lock);
- return err;
- }
- static int set_light_leds(struct light_state_t const *state, int type)
- {
- struct an30259a_pr_control led;
- memset(&led, 0, sizeof(led));
- switch (state->flashMode) {
- case LIGHT_FLASH_NONE:
- led.state = LED_LIGHT_OFF;
- break;
- case LIGHT_FLASH_TIMED:
- case LIGHT_FLASH_HARDWARE:
- led.state = LED_LIGHT_SLOPE;
- led.color = state->color & 0x00ffffff;
- // tweak to eliminate purplish tint from white color
- if (led.color == 0x00ffffff)
- led.color = 0x80ff80;
- // scale slope times based on flashOnMS
- led.time_slope_up_1 = (SLOPE_UP_1 * state->flashOnMS) / 1000;
- led.time_slope_up_2 = (SLOPE_UP_2 * state->flashOnMS) / 1000;
- led.time_slope_down_1 = (SLOPE_DOWN_1 * state->flashOnMS) / 1000;
- led.time_slope_down_2 = (SLOPE_DOWN_2 * state->flashOnMS) / 1000;
- led.mid_brightness = MID_BRIGHTNESS;
- led.time_off = state->flashOffMS;
- break;
- default:
- return -EINVAL;
- }
- return write_leds(&led);
- }
- static int set_light_leds_notifications(struct light_device_t *dev,
- struct light_state_t const *state)
- {
- return set_light_leds(state, 0);
- }
- static int set_light_leds_attention(struct light_device_t *dev,
- struct light_state_t const *state)
- {
- return set_light_leds(state, 1);
- }
- static int open_lights(const struct hw_module_t *module, char const *name,
- struct hw_device_t **device)
- {
- int (*set_light)(struct light_device_t *dev,
- struct light_state_t const *state);
- if (0 == strcmp(LIGHT_ID_BACKLIGHT, name))
- set_light = set_light_backlight;
- else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name))
- set_light = set_light_leds_notifications;
- else if (0 == strcmp(LIGHT_ID_ATTENTION, name))
- set_light = set_light_leds_attention;
- else
- return -EINVAL;
- pthread_once(&g_init, init_g_lock);
- struct light_device_t *dev = malloc(sizeof(struct light_device_t));
- memset(dev, 0, sizeof(*dev));
- dev->common.tag = HARDWARE_DEVICE_TAG;
- dev->common.version = 0;
- dev->common.module = (struct hw_module_t *)module;
- dev->common.close = (int (*)(struct hw_device_t *))close_lights;
- dev->set_light = set_light;
- *device = (struct hw_device_t *)dev;
- return 0;
- }
- static struct hw_module_methods_t lights_module_methods = {
- .open = open_lights,
- };
- const struct hw_module_t HAL_MODULE_INFO_SYM = {
- .tag = HARDWARE_MODULE_TAG,
- .version_major = 1,
- .version_minor = 0,
- .id = LIGHTS_HARDWARE_MODULE_ID,
- .name = "lights Module",
- .author = "Google, Inc.",
- .methods = &lights_module_methods,
- };
对于这个代码,主要是修改下
- char const *const LCD_FILE = "/sys/class/backlight/s6e8aa0/brightness";
背光其实就是打开这个节点,往里面写数据而已,所以,要把这个节点改为自己的平台的节点就可以了。
这里我们改为
- char const *const LCD_FILE = "/sys/class/backlight/pwm-backlight/brightness";
至于
- char const *const LED_FILE = "/dev/an30259a_leds";
这个,应该就是提示灯的节点吧,不管他。然后再mm下,得到了一个lights.default.so,然后替换掉这个.so就好了。
还有就是权限问题了,打开这个节点是要权限的,那么我们可以在init.xxx.rc中加上权限就好了。
- chown system system /sys/class/backlight/pwm-backlight/brightness
OK,这样,那么android那个调节屏幕亮度的UI界面就可以控制lcd的背光了。