Linux開發十五

lcd驅動

象棋小子 1048272975

lcd能夠支持彩色圖像的顯示和視頻的播放，是一種很重要的輸出設備，在一些嵌入式人機交互系統中，也往往需要lcd進行顯示。Linux內核已經支持了s3c2416的lcd控制器。

1. lcd設備

lcd設備包含了名字、獨有的資源等等一些驅動程序的硬件或自定義信息。通過platform_add_devices(platform_device_register)函數將定義的平臺設備註冊到內核中，用於匹配設備驅動。

內核在drivers\video\fbdev\s3c-fb.c中實現了s3c2416 lcd驅動，lcd設備平臺代碼如下。

static struct s3c_fb_pd_winhome2416_fb_win[] = {

[0]= {

.default_bpp = 16,

.max_bpp = 32,

.xres = 800,

.yres = 480,

};

static struct fb_videomodehome2416_lcd_timing = {

.pixclock = 41094,

.left_margin = 19,

.right_margin = 37,

.upper_margin = 10,

.lower_margin = 26,

.hsync_len = 27,

.vsync_len = 13,

.xres = 800,

.yres = 480,

};

static voids3c2416_fb_gpio_setup_24bpp(void)

{

unsignedint gpio;

for(gpio = S3C2410_GPC(1); gpio <= S3C2410_GPC(4); gpio++) {

s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));

s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);

}

for(gpio = S3C2410_GPC(8); gpio <= S3C2410_GPC(15); gpio++) {

s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));

s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);

}

for(gpio = S3C2410_GPD(0); gpio <= S3C2410_GPD(15); gpio++) {

s3c_gpio_cfgpin(gpio,S3C_GPIO_SFN(2));

s3c_gpio_setpull(gpio,S3C_GPIO_PULL_NONE);

}

static struct s3c_fb_platdatahome2416_fb_platdata = {

.win[0] = &home2416_fb_win[0],

.vtiming = &home2416_lcd_timing,

.setup_gpio = s3c2416_fb_gpio_setup_24bpp,

.vidcon0 = VIDCON0_VIDOUT_RGB | VIDCON0_PNRMODE_RGB,

.vidcon1 = VIDCON1_INV_HSYNC | VIDCON1_INV_VSYNC,

};

static struct resource s3c_fb_resource[]= {

[0]= DEFINE_RES_MEM(S3C_PA_FB, SZ_16K),

[1]= DEFINE_RES_IRQ(IRQ_LCD_VSYNC),

[2]= DEFINE_RES_IRQ(IRQ_LCD_FIFO),

[3]= DEFINE_RES_IRQ(IRQ_LCD_SYSTEM),

};

struct platform_device s3c_device_fb = {

.name = "s3c-fb",

.id = -1,

.num_resources = ARRAY_SIZE(s3c_fb_resource),

.resource = s3c_fb_resource,

.dev = {

.dma_mask = &samsung_device_dma_mask,

.coherent_dma_mask = DMA_BIT_MASK(32),

};

void __init s3c_fb_set_platdata(structs3c_fb_platdata *pd)

{

s3c_set_platdata(pd,sizeof(struct s3c_fb_platdata),

&s3c_device_fb);

}

在板級初始化函數home2416_machine_init()中加入lcd平臺數據s3c_fb_set_platdata(&home2416_fb_platdata)，在static struct platform_device *home2416_devices[]板級平臺設備列表中加入&s3c_device_fb，使lcd設備能夠註冊到內核中。

內核在drivers\video\backlight\ pwm_bl.c中實現了基於pwm方式的lcd背光驅動，背光設備平臺代碼如下。

static int s3c2416_backlight_init(structdevice *dev)

{

gpio_request(S3C2410_GPB(0),"Backlight");

gpio_direction_output(S3C2410_GPB(0),0);

s3c_gpio_setpull(S3C2410_GPB(0),S3C_GPIO_PULL_NONE);

s3c_gpio_cfgpin(S3C2410_GPB(0),S3C2410_GPB0_TOUT0);

return0;

}

static ints3c2416_backlight_notify(struct device *dev, int brightness)

{

if(!brightness) {

gpio_direction_output(S3C2410_GPB(0),0);

}else {

gpio_direction_output(S3C2410_GPB(0),0);

s3c_gpio_setpull(S3C2410_GPB(0),S3C_GPIO_PULL_NONE);

s3c_gpio_cfgpin(S3C2410_GPB(0),S3C2410_GPB0_TOUT0);

}

returnbrightness;

}

static voids3c2416_backlight_exit(struct device *dev)

{

gpio_direction_output(S3C2410_GPB(0),0);

}

static structplatform_pwm_backlight_data backlight_data = {

.max_brightness= 100,

.dft_brightness= 50,

.enable_gpio = -1,

.init = s3c2416_backlight_init,

.notify = s3c2416_backlight_notify,

.exit = s3c2416_backlight_exit,

};

static struct platform_devices3c2416_backlight = {

.name= "pwm-backlight",

.dev = {

.parent= &samsung_device_pwm.dev,

.platform_data= &backlight_data,

.id = -1,

};

static struct pwm_lookups3c2416_pwm_lookup[] = {

PWM_LOOKUP("samsung-pwm",0, "pwm-backlight", NULL, 36296,

PWM_POLARITY_NORMAL),

};

在板級初始化函數home2416_machine_init ()中把pwm背光映射到pwm設備表中pwm_add_table(s3c2416_pwm_lookup, ARRAY_SIZE(s3c2416_pwm_lookup))，在static struct platform_device *home2416_devices[]板級平臺設備列表中加入&s3c2416_backlight，使背光設備能夠註冊到內核中。

修改drivers\tty\vt\vt.c，禁止lcd開機一段時間後自動關屏。

static int blankinterval = 0;

修改drivers/video/console/fbcon.c，禁止光標閃爍。

static int fbcon_cursor_noblink = 1;

2. 內核配置

Linux配置支持lcd設備驅動，選中Device Drivers->Graphics support->Framebuffer Devices->Samsumg S3C framebuffer support 。

Linux配置支持lcd背光驅動，選中DeviceDrivers->Graphics support->Backlight & LCD device support->GenericPWM based Backlight Driver。

Linux配置開機logo，DeviceDrivers->Graphics support->Bootup logo->Standard 224-color Linux logo。

3. lcd測試

cat /proc/devices可以知道lcd主設備號爲29，次設備號爲0，在/dev目錄中創建fb0設備文件。

mknod /dev/fb0 c 29 0

lcd顯示黑屏。

mknod /dev/zero c 1 5

dd if=/dev/zero of=/dev/fb0

4. 應用編程

應用程序可以通過設備文件訪問lcd，lcd純色顯示應用測試代碼lcd_test.c如下。

#include "fcntl.h"

#include "unistd.h"

#include "stdio.h"

#include "stdlib.h"

#include "sys/mman.h"

void screen_clear(unsigned short*ppixel, unsigned short color)

{

inti;

for(i=0; i<800*480; i++)

ppixel[i]= color;

}

int main(void)

{

unsignedshort colors[] = {0xffff, 0x0000, 0xf800,

0x07e0,0x001f, 0xffe0, 0xf81f, 0x7ff};

intscreen_size;

intfd;

intindex;

unsignedshort *ppixel;

fd= open("/dev/fb0", O_RDWR);

if(fd == -1) {

printf("Openframebuffer failed\n");

exit(1);

}

screen_size= 800*480*2;

ppixel=(unsigned short *)mmap(0, screen_size,

PROT_READ|PROT_WRITE,MAP_SHARED, fd,0);

if(ppixel == (unsigned short *)-1) {

printf("Mapframebuffer failed\n");

exit(1);

}

while(1) {

screen_clear(ppixel,colors[index]);

index++;

if(index >= sizeof(colors)/sizeof(colors[0]))

index= 0;

sleep(2);

}

umap(ppixel,screen_size);

close(fd);

return0;

}

用arm-linux-gcc靜態編譯，使之生成arm cpu可執行的指令，並且可脫離任何庫獨立運行，arm-linux-gcc -static -o lcd_test lcd_test.c，生成lcd_test可執行文件。複製可執行文件到根文件系統，目標板啓動後在目錄輸入./lcd_test即可執行。