一.EDID数据格式：

EDID 1.3 data format

Byte sequence

00-19 Header information

00–07 Header information "00h FFh FFh FFh FFh FFh FFh 00h"

08–09

Manufacturer ID. These IDs are assigned by Microsoft. "00001=A”;

“00010=B”; ... “11010=Z”. Bit 7 (at address 08h) is 0, the first

character (letter) is located at bits 6 → 2 (at address 08h), the second

character (letter) is located at bits 1 & 0 (at address 08h) and

bits 7 → 5 (at address 09h), and the third character (letter) is located

at bits 4 → 0 (at address 09h).

10–11 Product ID Code (stored as LSB first). Assigned by manufacturer.

12–15

32-bit Serial Number. No requirement for the format. Usually stored as

LSB first. In order to maintain compatibility with previous

requirements the field should set at least one byte of the field to be

non-zero if an ASCII serial number descriptor is provided in the

detailed timing section.

16 Week of Manufacture. This varies by

manufacturer. One way is to count January 1–7 as week 1, January 8–15

as week 2 and so on. Some count based on the week number

(Sunday-Saturday). Valid range is 1-54.

17 Year of Manufacture. Add 1990 to the value for actual year.

18 EDID Version Number "01h"

19 EDID Revision Number "03h"

20-24 Basic display parameters

20 Video input definition

7 0=analog 1=digital

6 video level

00=0.7, 0.3; 01=0.714, 0.286; 10=1, 0.4; 11=0.7, 0

5

4 blank-to-black setup

3 separate syncs

2 composite sync

1 sync on green

0 serration vsync 1=DFP 1.x compatible

21 Maximum Horizontal Image Size (in centimeters).

22 Maximum Vertical Image Size (in centimetres).

23 Display Gamma. Divide by 100, then add 1 for actual value.

24 Power Management and Supported Feature(s):

7 standby

6 suspend

5 active-off/low power

4 Display type:

00=monochrome, 01=RGB colour, 10=non RGB multicolour, 11=undefined

3

2 standard colour space

1 preferred timing mode

0 default GTF supported

25-34 Chromaticity coordinates

25 low significant bits for Red X (bit 7-6), Red Y (bit 5-4), Green X (bit 3-2), Green Y (bit 1-0).

26 low significant bits for Blue X (bit 7-6), Blue Y (bit 5-4), White X (bit 3-2), White Y (bit 1-0).

27–34

high significant bits for Red X, Red Y, Green X, Green Y, Blue X, Blue

Y, White X, White Y. To decode actual value, rearrange bits as

follows: High significant bits 7-0 for (channel), low significant bits

for (channel). Actual value is between 0.000 and 0.999, but encoded

value is between 000h and 3FFh. Normalize by *999/1023.

35 Established timing I:

720×400@70 Hz, 720×400@88 Hz, 640×480@60 Hz, 640×480@67 Hz, 640×480@72 Hz, 640×480@75 Hz, 800×600@56 Hz, 800×600@60 Hz

36 Established timing II:

800×600@72

Hz, 800×600@75 Hz, 832×624@75 Hz, 1024×768@87 Hz (Interlaced),

1024×768@60 Hz, 1024×768@70 Hz, 1024×768@75 Hz, 1280×1024@75 Hz

37 Manufacturer's reserved timing:

00h for none

bit 7: 1152x870 @ 75 Hz (Mac II, Apple)

38–53 Standard timing identification

First byte: Horizontal resolution. Multiply by 8, then add 248 for actual value.

Second byte:

bit 7-6

Aspect ratio. Actual vertical resolution depends on horizontal resolution.

00=16:10, 01=4:3, 10=5:4, 11=16:9 (00=1:1 prior to v1.3)

bit 5-0

Vertical frequency. Add 60 to get actual value.

54–71 Descriptor Block 1

54–55 Pixel Clock (in 10 kHz) or 0 (55 MSB 54 LSB)

If Pixel Clock is non null:

56: Horizontal Active (in pixels)

57: Horizontal Blanking (in pixels)

58: Horizontal Active high (4 upper bits)

Horizontal Blanking high (4 lower bits)

59: Vertical Active (in lines)

60: Vertical Blanking (in lines)

61: high significant bits for Vertical Active (4 upper bits)

high significant bits for Vertical Blanking (4 lower bits)

62: Horizontal Sync Offset (in pixels)

63: Horizontal Sync Pulse Width (in pixels)

64: Vertical Sync Offset (in lines) (4 upper bits)

Vertical Sync Pulse Width (in lines) (4 lower bits)

65: high significant bits for Horizontal Sync Offset (bit 7-6)

high significant bits for Horizontal Sync Pulse Width (bit 5-4)

high significant bits for Vertical Sync Offset (bit 3-2)

high significant bits for Vertical Sync Pulse Width (bit 1-0)

66: Horizontal Image Size (in mm)

67: Vertical Image Size (in mm)

68: high significant bits for Horizontal Image Size (4 upper bits)

high significant bits for Vertical Image Size (4 lower bits)

69: Horizontal Border (in pixels representing only one side)

70: Vertical Border (in lines representing only one side)

71: Interlaced or not (bit 7)

Stereo or not (bit 6-5) ("00" means not)

Separate Sync or not (bit 4-3)

Vertical Sync positive or not (bit 2)

Horizontal Sync positive or not (bit 1)

Stereo Mode (bit 0) (unused if 6-5 are 00)

If Pixel Clock is null:

56: 0

57: Block type

FFh=Monitor Serial Number, FEh=ASCII string, FDh=Monitor Range Limits, FCh=Monitor name,

FBh=Colour Point Data, FAh, Standard Timing Data, F9h=Currently undefined,

0Fh=defined by manufacturer

58: 0

59–71: Descriptor block contents.

If block type is FFh, FEh, or FCh, the entire area is a text string.

If block type is FDh:

59–63:

Min Vertical frequency, Max Vertical frequency,

Min Horizontal frequency (in kHz), Max Horizontal frequency (in kHz), pixel clock

(in MHz (multiply by 10 for actual value))

64–65: Secondary GTF toggle

If encoded value is 000A, bytes 59-63 are used. If encoded value is 0200,

bytes 67–71 are used.

66: Start horizontal frequency (in kHz). Multiply by 2 for actual value.

67: C. Divide by 2 for actual value.

68-69: M (stored as LSB first).

70: K

71: J. Divide by 2 for actual value.

If block type is FBh:

59: W Index 0. If set to 0, bytes 60-63 are not used. If set to 1, 60–63 are

assigned to white point index #1

64: W Index 1. If set to 0, bytes 65-68 are not used. If set to 2, 65–68 are

assigned to white point index #2

White point index structure:

First byte

bit 3-2: low significant bits for White X (bit 3-2), White Y (bit 1-0)

Second to third byte: high significant bits for White X, White Y.

Fourth byte: Gamma. Divide by 100, then add 1 for actual value.

To decode White X and White Y, see bytes 25-34.

If block type is FAh:

59–70: Standard Timing Identification. 2 bytes for each record.

For structure details, see bytes 38-53.

72–89 Descriptor Block 2

90–107 Descriptor Block 3

108–125 Descriptor Block 4

126

Extension Flag.

This is the number of extension blocks which follow

this block. Prior to EDID 1.3, it is ignored, and should be set to 0.

127 Checksum.

This byte should be programmed such that the sum of all 128 bytes equals 00h.

CEA EDID Timing Extension Version 3 data format：

Byte sequence

00: Extension tag (which kind of extension block this is); 02h for CEA EDID

01: Revision number (Version number); 03h for Version 3

02: Byte number "d" within this block where the 18-byte DTDs begin. If no non-DTD data is present

in this extension block, the value should be set to 04h (the byte after next). If set to 00h,

there are no DTDs present in this block and no non-DTD data.

03: Number of DTDs present, other Version 2+ information

bit 7: 1 if display supports underscan, 0 if not

bit 6: 1 if display supports basic audio, 0 if not

bit 5: 1 if display supports YCbCr 4:4:4, 0 if not

bit 4: 1 if display supports YCbCr 4:2:2, 0 if not

bit 3..0: total number of native formats in the DTDs included in this block

04: Start of Data Block Collection. If byte 02 is set to 04h, this is where the DTD collection

begins. If byte 02 is set to another value, byte 04 is where the Data Block Collection begins,

and the DTD collection follows immediately thereafter.

The Data Block Collection contains one or more data blocks detailing video, audio, and speaker

placement information about the display. The blocks can be placed in any order, and the initial

byte of each block defines both its type and its length:

bit 7..5: Block Type Tag (1 is audio, 2 is video, 3 is vendor specific, 4 is speaker

allocation, all other values Reserved)

bit 4..0: Total number of bytes in this block following this byte

Once one data block has ended, the next byte is assumed to be the beginning of the next data

block. This is the case until the byte (designated in Byte 02, above) where the DTDs are known

to begin.

Any Audio Data Block contains one or more 3-byte Short Audio Descriptors (SADs). Each SAD

details audio format, channel number, and bitrate/resolution capabilities of the display as

follows:

SAD Byte 1 (format and number of channels):

bit 7: Reserved (0)

bit 6..3: Audio format code

1 = Linear Pulse Code Modulation (LPCM)

2 = AC-3

3 = MPEG1 (Layers 1 and 2)

4 = MP3

5 = MPEG2

6 = AAC

7 = DTS

8 = ATRAC

0, 15: Reserved

9 = One-bit audio aka SACD

10 = DD+

11 = DTS-HD

12 = MLP/Dolby TrueHD

13 = DST Audio

14 = Microsoft WMA Pro

bit 2..0: number of channels minus 1 (i.e. 000 = 1 channel; 001 = 2 channels; 111 =

8 channels)

SAD Byte 2 (sampling frequencies supported):

bit 7: Reserved (0)

bit 6: 192kHz

bit 5: 176kHz

bit 4: 96kHz

bit 3: 88kHz

bit 2: 48kHz

bit 1: 44kHz

bit 0: 32kHz

SAD Byte 3 (bitrate):

For LPCM, bits 7:3 are reserved and the remaining bits define bit depth

bit 2: 24 bit

bit 1: 20 bit

bit 0: 16 bit

For all other sound formats, bits 7..0 designate the maximum supported bitrate divided by

8kbps.

Any Video Data Block will contain one or more 1-byte Short Video Descriptors (SVDs). They are

decoded as follows:

bit 7: 1 to designate that this should be considered a "native" resolution, 0 for non-native

bit 6..0: index value to a table of standard resolutions/timings from CEA/EIA-861E:

Code

Short Aspect

Name Ratio HxV @ F

1 DMT0659 4:3 640x480p @ 59.94/60Hz

2 480p 4:3 720x480p @ 59.94/60Hz

3 480pH 16:9 720x480p @ 59.94/60Hz

4 720p 16:9 1280x720p @ 59.94/60Hz

5 1080i 16:9 1920x1080i @ 59.94/60Hz

6 480i 4:3 720(1440)x480i @ 59.94/60Hz

7 480iH 16:9 720(1440)x480i @ 59.94/60Hz

8 240p 4:3 720(1440)x240p @ 59.94/60Hz

9 240pH 16:9 720(1440)x240p @ 59.94/60Hz

10 480i4x 4:3 (2880)x480i @ 59.94/60Hz

11 480i4xH 16:9 (2880)x480i @ 59.94/60Hz

12 240p4x 4:3 (2880)x240p @ 59.94/60Hz

13 240p4xH 16:9 (2880)x240p @ 59.94/60Hz

14 480p2x 4:3 1440x480p @ 59.94/60Hz

15 480p2xH 16:9 1440x480p @ 59.94/60Hz

16 1080p 16:9 1920x1080p @ 59.94/60Hz

17 576p 4:3 720x576p @ 50Hz

18 576pH 16:9 720x576p @ 50Hz

19 720p50 16:9 1280x720p @ 50Hz

20 1080i25 16:9 1920x1080i @ 50Hz*

21 576i 4:3 720(1440)x576i @ 50Hz

22 576iH 16:9 720(1440)x576i @ 50Hz

23 288p 4:3 720(1440)x288p @ 50Hz

24 288pH 16:9 720(1440)x288p @ 50Hz

25 576i4x 4:3 (2880)x576i @ 50Hz

26 576i4xH 16:9 (2880)x576i @ 50Hz

27 288p4x 4:3 (2880)x288p @ 50Hz

28 288p4xH 16:9 (2880)x288p @ 50Hz

29 576p2x 4:3 1440x576p @ 50Hz

30 576p2xH 16:9 1440x576p @ 50Hz

31 1080p50 16:9 1920x1080p @ 50Hz

32 1080p24 16:9 1920x1080p @ 23.98/24Hz

33 1080p25 16:9 1920x1080p @ 25Hz

34 1080p30 16:9 1920x1080p @ 29.97/30Hz

35 480p4x 4:3 (2880)x480p @ 59.94/60Hz

36 480p4xH 16:9 (2880)x480p @ 59.94/60Hz

37 576p4x 4:3 (2880)x576p @ 50Hz

38 576p4xH 16:9 (2880)x576p @ 50Hz

39 1080i25 16:9 1920x1080i(1250 Total) @ 50Hz*

40 1080i50 16:9 1920x1080i @ 100Hz

41 720p100 16:9 1280x720p @ 100Hz

42 576p100 4:3 720x576p @ 100Hz

43 576p100H 16:9 720x576p @ 100Hz

44 576i50 4:3 720(1440)x576i @ 100Hz

45 576i50H 16:9 720(1440)x576i @ 100Hz

46 1080i60 16:9 1920x1080i @ 119.88/120Hz

47 720p120 16:9 1280x720p @ 119.88/120Hz

48 480p119 4:3 720x480p @ 119.88/120Hz

49 480p119H 16:9 720x480p @ 119.88/120Hz

50 480i59 4:3 720(1440)x480i @ 119.88/120Hz

51 480i59H 16:9 720(1440)x480i @ 119.88/120Hz

52 576p200 4:3 720x576p @ 200Hz

53 576p200H 16:9 720x576p @ 200Hz

54 576i100 4:3 720(1440)x576i @ 200Hz

55 576i100H 16:9 720(1440)x576i @ 200Hz

56 480p239 4:3 720x480p @ 239.76/240Hz

57 480p239H 16:9 720x480p @ 239.76/240Hz

58 480i119 4:3 720(1440)x480i @ 239.76/240Hz

59 480i119H 16:9 720(1440)x480i @ 239.76/240Hz

60 720p24 16:9 1280x720p @ 23.98/24Hz

61 720p25 16:9 1280x720p @ 25Hz

62 720p30 16:9 1280x720p @ 29.97/30Hz

63 1080p120 16:9 1920x1080p @ 119.88/120Hz

二.hdmi ddc bus是通过 i2c总线来通信的，因此要在kernel注册i2c驱动：

i2c驱动的设备节点是/dev/hdmi_ddc_misc,这个驱动非常的简单，只做了将35 byte的edid数据从kernel空间传到用户空间。

然后就可以在用户空间读到这35 byte的数据：

fh = open("/dev/hdmi_ddc_misc",O_RDWR);

if (fh == -1) {

printf("open hdmi_ddc device error! ");

return 0;

}

if(ioctl(fh,HDMI_DDC_I2C_READ,hdmi_edid_data)<0){

perror("ioctl error");

exit(1);

}

三.在用户空间对edid数据的解析：

//printf("Established timing monitor support:\n");

if(hdmi_edid_data[0] & ESTABLISHED_TIMING2)videoType |= (1 << VideoStd_640x480);

if(hdmi_edid_data[0] & ESTABLISHED_TIMING3)videoType |= (1 << VideoStd_640x480);

if(hdmi_edid_data[0] & ESTABLISHED_TIMING4)videoType |= (1 << VideoStd_640x480);

if(hdmi_edid_data[0] & ESTABLISHED_TIMING5)videoType |= (1 << VideoStd_640x480);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING14)videoType |= (1 << VideoStd_800x600);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING15)videoType |= (1 << VideoStd_800x600);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING9)videoType |= (1 << VideoStd_1024x768);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING10)videoType |= (1 << VideoStd_1024x768);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING11)videoType |= (1 << VideoStd_1024x768);

if(hdmi_edid_data[1] & ESTABLISHED_TIMING8)videoType |= (1 << VideoStd_1280x1024);

//printf("Standard timing monitor support:\n");

for(i=0;i<8;i++){

if(0x01 == hdmi_edid_data[i*2+2])goto st_end;

hsize = hdmi_edid_data[i*2+2]*8+248;

if(0x00 == (hdmi_edid_data[i*2+3] & 0xc0))vsize=hsize/16*10;

if(0x40 == (hdmi_edid_data[i*2+3] & 0xc0))vsize=hsize/4*3;

if(0x80 == (hdmi_edid_data[i*2+3] & 0xc0))vsize=hsize/5*4;

if(0xc0 == (hdmi_edid_data[i*2+3] & 0xc0))vsize=hsize/16*9;

rate = (hdmi_edid_data[i*2+3] & 0x3f)+60;

//printf("monitor support %dx%d@%d Hz\n",hsize,vsize,rate);

if((640 == hsize) && (480 == vsize))videoType |= (1 << VideoStd_640x480);

if((720 == hsize) && (480 == vsize))videoType |= (1 << VideoStd_720x480);

if((800 == hsize) && (480 == vsize))videoType |= (1 << VideoStd_800x480);

if((800 == hsize) && (600 == vsize))videoType |= (1 << VideoStd_800x600);

if((1024 == hsize) && (768 == vsize))videoType |= (1 << VideoStd_1024x768);

if((1280 == hsize) && (720 == vsize))videoType |= (1 << VideoStd_1280x720);

if((1280 == hsize) && (1024 == vsize))videoType |= (1 << VideoStd_1280x1024);

if((1600 == hsize) && (900 == vsize))videoType |= (1 << VideoStd_1600x900);

if((1920 == hsize) && (1080 == vsize))videoType |= (1 << VideoStd_1920x1080);

}

st_end:

//printf("CEA EDID Timing monitor support:\n");

if(0x01 != hdmi_edid_data[18])goto cet_end;

for(i=20;i<35;i++){

if(1 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_640x480);

if(2 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(3 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(48 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(49 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(56 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(57 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_720x480);

if(4 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(19 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(41 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(47 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(60 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(61 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(62 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1280x720);

if(16 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

if(31 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

if(32 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

if(33 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

if(34 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

if(63 == (hdmi_edid_data[i] & 0x7f))videoType |= (1 << VideoStd_1920x1080);

}

cet_end:

四.数据协商，设置一种最佳的分辨率：

if(videoType & (1 << VideoStd_1280x720)) {

current_videotype = VideoStd_1280x720;

goto display_set_end;

}

if(videoType & (1 << VideoStd_1600x900)) {

current_videotype = VideoStd_1600x900;

SysFs_change(Display_Output_DVI, VideoStd_1600x900);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1280x1024)){

current_videotype = VideoStd_1280x1024;

SysFs_change(Display_Output_DVI, VideoStd_1280x1024);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1024x768)) {

current_videotype = VideoStd_1024x768;

SysFs_change(Display_Output_DVI, VideoStd_1024x768);

goto display_set_end;

}

if(videoType & (1 << VideoStd_800x480)) {

current_videotype = VideoStd_800x480;

SysFs_change(Display_Output_DVI, VideoStd_800x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_800x600)) {

current_videotype = VideoStd_800x600;

SysFs_change(Display_Output_DVI, VideoStd_800x600);

goto display_set_end;

}

if(videoType & (1 << VideoStd_640x480)) {

current_videotype = VideoStd_640x480;

SysFs_change(Display_Output_DVI, VideoStd_640x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_720x480)) {

current_videotype = VideoStd_720x480;

SysFs_change(Display_Output_DVI, VideoStd_720x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1920x1080)){

current_videotype = VideoStd_1920x1080;

SysFs_change(Display_Output_DVI, VideoStd_1920x1080);

goto display_set_end;

}

display_set_end:

五.提供给用户的API:

1.得到显示器支持的分辨率：

int get_monitor_support_video_type(void)

{

return videoType;

}

2.得到设备当前的分辨率：

int get_current_video_type(void)

{

return current_videotype;

}

3.设置分辨率：int set_video_type(int videoType)

{

if(videoType & (1 << VideoStd_1280x720)) {

SysFs_change(Display_Output_DVI, VideoStd_1280x720);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1600x900)) {

SysFs_change(Display_Output_DVI, VideoStd_1600x900);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1280x1024)){

SysFs_change(Display_Output_DVI, VideoStd_1280x1024);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1024x768)) {

SysFs_change(Display_Output_DVI, VideoStd_1024x768);

goto display_set_end;

}

if(videoType & (1 << VideoStd_800x480)) {

SysFs_change(Display_Output_DVI, VideoStd_800x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_800x600)) {

SysFs_change(Display_Output_DVI, VideoStd_800x600);

goto display_set_end;

}

if(videoType & (1 << VideoStd_640x480)) {

SysFs_change(Display_Output_DVI, VideoStd_640x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_720x480)) {

SysFs_change(Display_Output_DVI, VideoStd_720x480);

goto display_set_end;

}

if(videoType & (1 << VideoStd_1920x1080)){

SysFs_change(Display_Output_DVI, VideoStd_1920x1080);

goto display_set_end;

}

display_set_end:

return 0;

}