购买Raspberry Pi V2后，还得为他配置其他一些周边器件，如5V2A的micro usb电源线、显示器、键盘、鼠标等。手头上有N多VGA显示器，却没一台DVI的，没办法，淘宝上买了专门针对树莓派生产的电源（18RMB）和hdmi转vga线（70RMB）。
按照网上的一些说法，先通过SSH登录进去，把/boot/config.txt里的几个参数放出：
hdmi_safe=1 disable_overscan=1 overscan_left=-30 overscan_right=-30 overscan_top=-30 overscan_bottom=-30 hdmi_force_hotplug=1 hdmi_group=2 hdmi_mode=16 hdmi_drive=2 config_hdmi_boost=4
注意，必须把hdmi_drive设为2，因为1是DVI输出，2才是hdmi输出，因为我的线是hdmi转vga的。
这样，重新启动Pi后，基本能显示了，可是默认是640×480的，看着非常别扭，网上找了很多资料，包括把如下config.txt部分放开：
framebuffer_width=1280 framebuffer_height=960
貌似分辨率成了1280×960，而实际上是，只是Pi按1280×960输出到屏幕上了，而屏幕的分辨率还是640×480的，所以字体很虚很模糊，几乎看不清。
按理说只要更改
hdmi_group=2 —>1:CEA 2:DMT
hdmi_mode=4 —>从模式列表中选取一种显示模式
就可以切换显示分辨率了，可是怎么改都没啥用。貌似不起任何作用！
幸好看了完整的Raspberry Pi配置说明，发现当hdmi_safe设置为1时，hdmi_group默认为1，hdmi_mode为1，后面你怎么改hdmi_group和hdmi_mode都不起作用了！！！
## hdmi_safe ## Use "safe mode" settings to try to boot with maximum hdmi compatibility. ## ## Value Description ## ------------------------------------------------------------------------- ## 0 Disabled (Default) ## 1 Enabled (this does: hdmi_force_hotplug=1, config_hdmi_boost=4, ## hdmi_group=1, hdmi_mode=1, ## disable_overscan=0) ## #hdmi_safe=1
注意看完整的Raspberry Pi配置说明，你会发现，当disable_overscan=1时，overscan_top、overscan_botom、overscan_left、overscan_right几个参数不起作用！
################################################################################ ## Overscan Video Settings ################################################################################ ## overscan_left ## Number of pixels to skip on left ## #overscan_left=0 ## overscan_right ## Number of pixels to skip on right ## #overscan_right=0 ## overscan_top ## Number of pixels to skip on top ## #overscan_top=0 ## overscan_bottom ## Number of pixels to skip on bottom ## #overscan_bottom=0 ## disable_overscan ## Set to 1 to disable overscan ## ## Value Description ## ------------------------------------------------------------------------- ## 0 Overscan Enabled (Default) ## 1 Overscan Disabled ## #disable_overscan=1
所以，最后我的配置文件是这样的：
pi@raspberrypi:/boot$ vi config.txt #hdmi_edid_file=1 # uncomment if you get no picture on HDMI for a default "safe" mode #hdmi_safe=1 # uncomment this if your display has a black border of unused pixels visible # and your display can output without overscan disable_overscan=1 # uncomment the following to adjust overscan. Use positive numbers if console # goes off screen, and negative if there is too much border #overscan_left=-30 #overscan_right=-30 #overscan_top=-30 #overscan_bottom=-30 # uncomment to force a console size. By default it will be display's size minus # overscan. #framebuffer_width=1280 #framebuffer_height=720 # uncomment if hdmi display is not detected and composite is being output hdmi_force_hotplug=1 # uncomment to force a specific HDMI mode (this will force VGA) hdmi_group=2 hdmi_mode=32 # uncomment to force a HDMI mode rather than DVI. This can make audio work in # DMT (computer monitor) modes hdmi_drive=2 # uncomment to increase signal to HDMI, if you have interference, blanking, or # no display config_hdmi_boost=4 # uncomment for composite PAL #sdtv_mode=2 #uncomment to overclock the arm. 700 MHz is the default. #arm_freq=800 # for more options see http://elinux.org/RPi_config.txt
绝对完美运行。
一个对hdmi_safe=1的不了解，折腾了我这么多天，真是不值啊。
后面写的就不用看了，都是以前走的弯路，那个弯啊，绕啊，希望你们就别走了……
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用tvservice -d edid.dat将edid数据导出到edid.dat：
pi@raspberrypi:/opt/vc/bin$ tvservice -d edid.dat Written 0 bytes to edid.dat
没数据。。。
使用tvservice -s查看当前的显示状态
pi@raspberrypi:~$ tvservice -s state: HPD high|HDMI mode|HDCP off|composite off (0x12001a), 640x480 @ 60Hz, progressive
的确是640×480 @ 60 Hz显示的。再用-m查看支持的显示，却发现只有一种CEA模式，而DMT模式根本就没有：
pi@raspberrypi:~$ tvservice -m CEA
Group CEA has 1 modes:
mode 1: 640x480 @ 60Hz, progressive
pi@raspberrypi:~$ tvservice -m DMT
Group DMT has 0 modes:
这就难怪怎么改config.txt中的hdmi_group和hdmi_mode都没用的原因了！！！
网上翻了很多资料，终于发现，只要在config.txt文件开头加入如下信息，重启，终于以更高的分辨率显示了：
hdmi_edid_file=1
hdmi_edid_file默认为0，表示从设备读取edid信息，如果为1，则强制从edid.txt文件读取edid信息。
启动后，进入终端，查看当前状态：
pi@raspberrypi:~$ tvservice -s state: HPD high|HDMI mode|HDCP off|composite off (0x12001a), 1280x720 @ 60Hz, progressive
可见现在的显示模式是 1280×720 @ 60Hz。
现在hdmi是如下配置的：
hdmi_group=1 hdmi_mode=16
貌似这个值不起作用了。
很疑惑，这个edid.txt文件在哪里？？？如果不存在，是否可以通过导入一个edit.txt文件来达到配置显示分辨率的目的呢？
附：
从这里http://elinux.org/RPiconfig可以看到group和mode的对应关系，相应的修改即可：
These values are valid if hdmi_group=1 (CEA) hdmi_mode=1 VGA hdmi_mode=2 480p 60Hz hdmi_mode=3 480p 60Hz H hdmi_mode=4 720p 60Hz hdmi_mode=5 1080i 60Hz hdmi_mode=6 480i 60Hz hdmi_mode=7 480i 60Hz H hdmi_mode=8 240p 60Hz hdmi_mode=9 240p 60Hz H hdmi_mode=10 480i 60Hz 4x hdmi_mode=11 480i 60Hz 4x H hdmi_mode=12 240p 60Hz 4x hdmi_mode=13 240p 60Hz 4x H hdmi_mode=14 480p 60Hz 2x hdmi_mode=15 480p 60Hz 2x H hdmi_mode=16 1080p 60Hz hdmi_mode=17 576p 50Hz hdmi_mode=18 576p 50Hz H hdmi_mode=19 720p 50Hz hdmi_mode=20 1080i 50Hz hdmi_mode=21 576i 50Hz hdmi_mode=22 576i 50Hz H hdmi_mode=23 288p 50Hz hdmi_mode=24 288p 50Hz H hdmi_mode=25 576i 50Hz 4x hdmi_mode=26 576i 50Hz 4x H hdmi_mode=27 288p 50Hz 4x hdmi_mode=28 288p 50Hz 4x H hdmi_mode=29 576p 50Hz 2x hdmi_mode=30 576p 50Hz 2x H hdmi_mode=31 1080p 50Hz hdmi_mode=32 1080p 24Hz hdmi_mode=33 1080p 25Hz hdmi_mode=34 1080p 30Hz hdmi_mode=35 480p 60Hz 4x hdmi_mode=36 480p 60Hz 4xH hdmi_mode=37 576p 50Hz 4x hdmi_mode=38 576p 50Hz 4x H hdmi_mode=39 1080i 50Hz reduced blanking hdmi_mode=40 1080i 100Hz hdmi_mode=41 720p 100Hz hdmi_mode=42 576p 100Hz hdmi_mode=43 576p 100Hz H hdmi_mode=44 576i 100Hz hdmi_mode=45 576i 100Hz H hdmi_mode=46 1080i 120Hz hdmi_mode=47 720p 120Hz hdmi_mode=48 480p 120Hz hdmi_mode=49 480p 120Hz H hdmi_mode=50 480i 120Hz hdmi_mode=51 480i 120Hz H hdmi_mode=52 576p 200Hz hdmi_mode=53 576p 200Hz H hdmi_mode=54 576i 200Hz hdmi_mode=55 576i 200Hz H hdmi_mode=56 480p 240Hz hdmi_mode=57 480p 240Hz H hdmi_mode=58 480i 240Hz hdmi_mode=59 480i 240Hz H H means 16:9 variant (of a normally 4:3 mode). 2x means pixel doubled (i.e. higher clock rate, with each pixel repeated twice) 4x means pixel quadrupled (i.e. higher clock rate, with each pixel repeated four times)
These values are valid if hdmi_group=2 (DMT) hdmi_mode=1 640x350 85Hz hdmi_mode=2 640x400 85Hz hdmi_mode=3 720x400 85Hz hdmi_mode=4 640x480 60Hz hdmi_mode=5 640x480 72Hz hdmi_mode=6 640x480 75Hz hdmi_mode=7 640x480 85Hz hdmi_mode=8 800x600 56Hz hdmi_mode=9 800x600 60Hz hdmi_mode=10 800x600 72Hz hdmi_mode=11 800x600 75Hz hdmi_mode=12 800x600 85Hz hdmi_mode=13 800x600 120Hz hdmi_mode=14 848x480 60Hz hdmi_mode=15 1024x768 43Hz DO NOT USE hdmi_mode=16 1024x768 60Hz hdmi_mode=17 1024x768 70Hz hdmi_mode=18 1024x768 75Hz hdmi_mode=19 1024x768 85Hz hdmi_mode=20 1024x768 120Hz hdmi_mode=21 1152x864 75Hz hdmi_mode=22 1280x768 reduced blanking hdmi_mode=23 1280x768 60Hz hdmi_mode=24 1280x768 75Hz hdmi_mode=25 1280x768 85Hz hdmi_mode=26 1280x768 120Hz reduced blanking hdmi_mode=27 1280x800 reduced blanking hdmi_mode=28 1280x800 60Hz hdmi_mode=29 1280x800 75Hz hdmi_mode=30 1280x800 85Hz hdmi_mode=31 1280x800 120Hz reduced blanking hdmi_mode=32 1280x960 60Hz hdmi_mode=33 1280x960 85Hz hdmi_mode=34 1280x960 120Hz reduced blanking hdmi_mode=35 1280x1024 60Hz hdmi_mode=36 1280x1024 75Hz hdmi_mode=37 1280x1024 85Hz hdmi_mode=38 1280x1024 120Hz reduced blanking hdmi_mode=39 1360x768 60Hz hdmi_mode=40 1360x768 120Hz reduced blanking hdmi_mode=41 1400x1050 reduced blanking hdmi_mode=42 1400x1050 60Hz hdmi_mode=43 1400x1050 75Hz hdmi_mode=44 1400x1050 85Hz hdmi_mode=45 1400x1050 120Hz reduced blanking hdmi_mode=46 1440x900 reduced blanking hdmi_mode=47 1440x900 60Hz hdmi_mode=48 1440x900 75Hz hdmi_mode=49 1440x900 85Hz hdmi_mode=50 1440x900 120Hz reduced blanking hdmi_mode=51 1600x1200 60Hz hdmi_mode=52 1600x1200 65Hz hdmi_mode=53 1600x1200 70Hz hdmi_mode=54 1600x1200 75Hz hdmi_mode=55 1600x1200 85Hz hdmi_mode=56 1600x1200 120Hz reduced blanking hdmi_mode=57 1680x1050 reduced blanking hdmi_mode=58 1680x1050 60Hz hdmi_mode=59 1680x1050 75Hz hdmi_mode=60 1680x1050 85Hz hdmi_mode=61 1680x1050 120Hz reduced blanking hdmi_mode=62 1792x1344 60Hz hdmi_mode=63 1792x1344 75Hz hdmi_mode=64 1792x1344 120Hz reduced blanking hdmi_mode=65 1856x1392 60Hz hdmi_mode=66 1856x1392 75Hz hdmi_mode=67 1856x1392 120Hz reduced blanking hdmi_mode=68 1920x1200 reduced blanking hdmi_mode=69 1920x1200 60Hz hdmi_mode=70 1920x1200 75Hz hdmi_mode=71 1920x1200 85Hz hdmi_mode=72 1920x1200 120Hz reduced blanking hdmi_mode=73 1920x1440 60Hz hdmi_mode=74 1920x1440 75Hz hdmi_mode=75 1920x1440 120Hz reduced blanking hdmi_mode=76 2560x1600 reduced blanking hdmi_mode=77 2560x1600 60Hz hdmi_mode=78 2560x1600 75Hz hdmi_mode=79 2560x1600 85Hz hdmi_mode=80 2560x1600 120Hz reduced blanking hdmi_mode=81 1366x768 60Hz hdmi_mode=82 1080p 60Hz hdmi_mode=83 1600x900 reduced blanking hdmi_mode=84 2048x1152 reduced blanking hdmi_mode=85 720p 60Hz hdmi_mode=86 1366x768 reduced blanking
找了一下午，终于在看到楼主这篇Blog的时候成功了，跪谢T－T
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