kernel panic 其实是电源不够引起的，至少要5V1A的电源。我用3星700mA的充电器就kernel panic,用糯鸡鸭5V1200mA的就可以。
http://elinux.org/RPi_Hardware#Power_Supply_Problems
Power Supply Problems
电源问题
There have been a number of problems reported that seem to be caused by inadequate power, this is an attempt to explain what is needed and the consequences of not having enough power.
许多人报告了由于电源不足而引发的问题。这里尝试解释我们需要什么以及缺乏足够电力所造成的后果。
The power required by the Pi will vary depending on how busy it is and what peripherals are connected.
派所需要的电能会变化，具体取决于系统的繁忙程度和所连接的设备多寡。
Running a GUI will take more power.
The USB devices and Ethernet connection will take power.
Running software will take power.
使用图形界面（比纯字符界面）更耗电
连usb设备和网线更耗电
运行程序也会耗电
This means that it's difficult to say exactly how much power is needed. People have reported current requirements of between 300mA and 550mA. But it could in reality take more, especially for short periods. A simple multimeter will not show short surges on the power requirement. A surge in the power requirement for a few milliseconds will not be detectable by a meter but will be enough to cause problems. If the board does not get enough power the voltage will drop. If it drops enough parts of the system will run unreliably because data can get corrupted. The USB IC runs on 5V and handles the USB and Ethernet ports so it's likely that this will be the first thing to fail. Problems seen are unreliable Ethernet connection and unreliable operation of the Keyboard and/or mouse. Each of the two USB ports on the Pi has a fuse rated at 140 mA, so any connected USB devices should draw less than this amount of current. Some USB WiFi dongles are known to draw more than 150 mA when configured and active. The microUSB input port has a 700 mA polyfuse which may have enough resistance to cause a significant voltage drop on the board, even below 700 mA total current.
这意味着，很难具体说清楚要多少电。人们报告说现在的要求在300mA到550mA之间。但是实际可能耗得更多，特别是瞬时电流可能不止这个数目。用万用表测出来的值是平均值，无法反映瞬时波动对电能需求的影响。在几毫秒中电流需求的猛增不会反映在万用表测量值上，但它已经足够让机器出问题了。若板子拿不到足够电能，电压会降低。若电压降得够低，树莓派的部分系统就会挂掉，因为此时系统里得到的数据可能会坏掉。USB IC运作在5V电压下，它负责处理usb和网卡接口，如果电能不够，第一个完蛋的应该就是它了。这时可以发现网卡没法用（例如一接网线就kernel panic），键盘鼠标也动不了了（这时鼠标底下的红灯是不亮的，没电了嘛）。派的每个USB接口的极限供电(fuse)是140mA，所以任何与它连接的usb设备的耗电都应该小于这个值。已知有些USB WiFi卡在配置运作时耗电大于150mA。microUSB输入口有个700mA的ployfuse(多晶硅熔线，一颗压敏电阻)，这个阻抗也许足够导致板子的电压下降了——即使总电流小于700mA。
There are several reasons why the power to the board may be inadequate:
有些原因导致电源不够：
The PSU may not deliver enough power. Although the maximum power requirement is said to be 700mA, that is with no peripherals connected (USB, Ethernet etc), so a 1000mA PSU should be regarded as a minimum. This allows some leeway in case the power supply cannot deliver it's full power without the voltage dropping.
The PSU is not regulated.
The cable connecting the PSU to the Pi may not be good. People have reported cables with 4 ohms resistance on the power connections. At 500mA drain this would reduce a 5V supply to 3V.
电源（Power Supply Unit）供电不足。尽管最大电流需求应该在700mA，但那是什么也没连（无网线/USB）的时候的值。所以至少要1000mA的电源。这样做，对于「不掉电压就不能足够供电」的情况，就留有余地了。
电源不合规格。
电源连树莓派的线不好。有人报告有的电源连线有4欧姆阻抗。若电流是500mA，这电压到板子上就只剩3V了。
How Can I tell if the power supply is inadequate?
那我咋知道电源不足呢？
Common symptoms of an inadequate power supply are
电能不足的典型症状如下：
Unreliable Ethernet or keyboard operation, especially if it's OK at first but not when the GUI is started.
SD card errors at start up seems to be another symptom of poor power.
网线或键盘用着用着就悲剧了，特别是在「一开始OK，但是开了GUI之后系统不动了」的时候
启动时的SD卡错误似乎也是电源不足的另一个症状
If you think you have a problem with your power supply, it is a good idea to check the actual voltage on the Raspberry Pi circuit board. Two test points labelled TP1 and TP2 are provided on the circuit board to facilitate voltage measurements.
如果你觉得你的电源供应有问题，最好测测树莓派电路板上实际电压。电路板上提供了名为TP1和TP2的两个测试点来测电压。
Use a multimeter which is set to the range 20 volts DC (or 20v =). You should see a voltage between 4.75 and 5.25 volts. Anything outside this range indicates that you have a problem with your power supply or your power cable. Anything inside, but close to the limits, of this range may indicate a problem.
使用量程设为20V DC 的万用表。电压应在4.75〜5.25V之间。此范围外的电压说明你的供电有问题；虽未超限，不过很接近这个极值的话可能也有问题。
RPI Test Points.JPG Voltmeter.JPG
It has been reported by a number of users that Apple iPhone and iPad USB power supplies are inadequate for powering the R-Pi. ([5]).
据许多用户报道，水果的iPhone and iPad USB充电器带不动树莓派。（）
what is ployfuse?
Poly Fuse表面意思即是多狀態保險絲，也被稱為可復式保險，提供過壓/過流保護。它的本質是一顆壓敏電阻，當電壓在正常范圍時，它的電阻很小(或很大)，當電壓達到某一高值時，它的電阻將驟變，變得極大(或極小)。當電磁恢復正常時，Poly Fuse恢復到正常狀態。Poly Fuse的變化特性根據實際應用的電路不同而選擇。在外設的接口數據電路中，受到外界高電壓瞬間衝擊的可能性很大，譬如熱插拔、雷擊等，Poly Fuse需要起的是避雷針的作用，它與接口電路和主板的電源地並聯，正常情況下電阻為無窮大，相當於斷路，並不影響電路的正常運\作，當瞬間高壓出現時，Poly Fuse立刻對地短路，短時間內將電流導走，保護主板接口和外設的安全。還有一些有源設備、或外設的供電接口上可能會出現過大電流，為了保護這些設備的安全，選擇的Poly Fuse就應該類似熔斷式保險絲，把它串聯在電路中，當電流過大時瞬間阻值增大，相當於斷路，從而起到保護作用。
http://www.shumeipai.net/read.php?tid-260.html
因为基本在输入账号密码的过程中，按一下“p”要么没反应，要反应就变成了“pppppppppppp”，
典型供电不足。 |
楼主
发表于 2012-6-17 23:07:20
5月下旬订货,今天DHL送到了;可惜要出差,周末才能测试.
