Sabrelite开发板接LCD显示器无信号的解决方法

       很多购买了英蓓特公司Sabrelite开发板的同学在使用HDMI-DVI转接线连接显示器时，出现了无法显示的问题，并且串行调试信号显示乱码。都是用5V 4A的原装电源，产品自带的微型SD卡，而且用“串行转USB”转换器连接调试线缆，找不到问题所在。

       这里要指出的是，通常这样的问题与HDMI-DVI转接没有半毛钱的关系。使用HDMI显示器有个现象，就是从开始启动到启动基本结束的一分钟左右时间内看不到任何显示，直到最后出现“Starting demo…”才会有信号。这个demo只是Timesys的一个推广内容，包含一些PPT页面，恕我直言，这个demo除了告诉你Sabrelite启动成功以外毫无用处。。。（扯远了）这是因为产品附带的SD卡中只有一个demo，所以在Sabrelite完全启动并运行demo程序之前不可能看到任何图像，而这之前的输出信号都是走串行接口出来的。另外，Sabrelite附带的单页说明书太简单，应该指明将串行线缆连接到板上标记为“debug”的接口上才对。

       如果等很久还是无法从SD卡启动demo，那么就需要从串行终端来判断原因了。我倾向于逐一排查。
1. 通电后用万用表测量供电单元。
2. 确保串行线正确的连接到J17接口。
3. 确认串行线是否无损伤，因为串行线确实很脆弱。
4. 确认终端程序配置的串行接口与USB适配器相匹配，并且配置参数为115200、8、None、1（串口乱码多半是两端数据速率不匹配）
5. 确保两个SW1 DIP开关为OFF状态，即拨杆朝向开发板的边缘，而不是朝向处理器。

       你可以先拿掉SD卡尝试启动，这时仍然可以看到串行接口的输出，因为板上的flash存储器里的u-boot bootloader仍然会工作。只要初始化正常了，然后再把SD卡插回去试试看会不会报错。

        这下面的内容是启动信息以供参考。（注意，为了避免伤到同学们的脑细胞，我从几百行内核启动信息中截取了一部分，这样也容易阅读）。

U-Boot 2009.08 (Aug 16 2012 - 10:06:42)

CPU:   Freescale i.MX 6 family 0.0V at 792 MHz
Temperature:   22 C, calibration data 0x5b45227d
mx6q pll1: 792MHz
mx6q pll2: 528MHz
mx6q pll3: 480MHz
mx6q pll8: 50MHz
ipg clock     : 66000000Hz
ipg per clock : 66000000Hz
uart clock    : 80000000Hz
cspi clock    : 60000000Hz
ahb clock     : 132000000Hz
axi clock   : 264000000Hz
emi_slow clock: 29333333Hz
ddr clock     : 528000000Hz
usdhc1 clock  : 200000000Hz
usdhc2 clock  : 200000000Hz
usdhc3 clock  : 200000000Hz
usdhc4 clock  : 200000000Hz
NFC clock     : 24000000Hz
Board: MX6Q-SABRELITE:[ POR]
Boot Device: I2C
I2C:   ready
DRAM:   1 GB
MMC:   FSL_USDHC: 0,FSL_USDHC: 1
JEDEC ID: 0xbf:0x25:0x41
Reading SPI NOR flash 0xc0000 [0x2000 bytes] -> ram 0x276009b8
SUCCESS

*** Warning - bad CRC, using default environment

In:    serial
Out:   serial
Err:   serial
Net:   got MAC address from IIM: 00:00:00:00:00:00
FEC0 [PRIME]
Hit any key to stop autoboot:  3
Card did not respond to voltage select!
mmc0(part 0) is current device
MMC: block number 0x1 exceeds max(0x0)
** Can't read from device 0 **

** Unable to use mmc 0:1 for fatload **
** Bad partition 1 **
mmc1 is current device
reading /6q_bootscript

** Unable to read "/6q_bootscript" from mmc 1:1 **
Loading file "/6q_bootscript" from mmc device 1:1 (xxb1)
361 bytes read
## Executing script at 10008000
Loading file "/boot/uImage" from mmc device 1:1 (xxb1)
3627844 bytes read
## Booting kernel from Legacy Image at 10800000 ...
   Image Name:   Linux-3.0.15-ts-armv7l
   Image Type:   ARM Linux Kernel Image (uncompressed)
   Data Size:    3627780 Bytes =  3.5 MB
   Load Address: 10008000
   Entry Point:  10008000
   Verifying Checksum ... OK
   Loading Kernel Image ... OK
OK

Starting kernel ...

Uncompressing Linux... done, booting the kernel.
Linux version 3.0.15-ts-armv7l (fourier@fourier-desktop) (gcc version 4.6.3 (Timesys 20120813) ) #1 SMP PREEMPT
CPU: ARMv7 Processor [412fc09a] revision 10 (ARMv7), cr=10c53c7d
CPU: VIPT nonaliasing data cache, VIPT aliasing instruction cache
Machine: Freescale i.MX 6Quad Sabre-Lite Board
Memory policy: ECC disabled, Data cache writealloc
PERCPU: Embedded 7 pages/cpu @8c008000 s5440 r8192 d15040 u32768
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 227328
Kernel command line: console=ttymxc1,115200 video=mxcfb0:dev=hdmi,1280x720M@60,if=RGB24 video=mxcfb1:dev=ldb,LDB

[.. lots of kernel messages deleted ..]

kjournald starting.  Commit interval 5 seconds
EXT3-fs (mmcblk0p1): using internal journal
EXT3-fs (mmcblk0p1): recovery complete
EXT3-fs (mmcblk0p1): mounted filesystem with writeback data mode
VFS: Mounted root (ext3 filesystem) on device 179:1.
Freeing init memory: 208K
init started: BusyBox v1.20.2 (2012-08-16 10:09:55 EDT)
Thermal: fuse data 0x5b45227d
Setting hotplug handler: [ OK ]
Creating device files: Auto-mount of [/media/mmcblk0p1] successful
[ OK ]
modprobe: module egalax_ts not found in modules.dep
modprobe: module ft5x06_ts not found in modules.dep
modprobe: module tsc2004 not found in modules.dep
Starting system logging.
Configuring network interfaces: done
Starting dropbear sshd: OK
Finding touchscreen using legacy method:[FAIL]
Finding mouse:[FAIL]
Framebuffer fb0
Resolution 1152 864
Screen resolution: 1152 x 864
HDMI display
Search for input device Acer T230H
Mouse device is Auto
cat: can't open '/etc/ts.dev': No such file or directory
Starting demo...
Starting demo...


BusyBox v1.20.2 (2012-08-16 10:09:55 EDT) built-in shell (ash)
Enter 'help' for a list of built-in commands.

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