Horace papa's life

First of all let me give you a brief on the insides of Ethernet MAC.
We have a MAC module which interacts with Physical layer and we have DMA which interacts with memory. So the Ethernet frame flow is like this

Transmit:
Memory-->DMA-->MAC-->Physical Layer
Receive:
Memory<--DMA<--MAC<--Physical Layer

Transmit and receive descriptors are basically used by DMA. In these descriptors, we  give address of  memory location from where DMA reads and writes back the Ethernet frame while transmitting and receiving respectively. Apart from memory location,  many other important parameters which  are required by DMA  to process a frame are programmed in descriptors.Once all the information is programmed, we give the control of descriptors to DMA. We can have one or many descriptors for one frame. When transmit or receive of frame is complete , DMA updates the status in descriptors and assign them back to user. Once we read status and frame data,  we again give control of descriptors back to DMA and the process continues.
It's our choice how many descriptors we want to program. The more descriptors we program...the more frames we can process in one go (high performance) but yes at the cost of more kernel resources. There is always a trade off in kernel.

使用 screen

在命令列下打 screen 就會進入 screen 的天地：

% screen

注意，所有 screen 的指令都是以 Ctrl 鍵加上 a 鍵開始的，在之後以 C-a 代表，C-a c 代表按住 Ctrl 鍵不放再按 a 鍵，然後放開按 c 鍵；而 C-a C-c 代表按住 Ctrl 鍵不放再按 a 鍵，然後放開後再按住 Ctrl 鍵不放按 c 鍵。

開啟，關閉，切換

C-a c 或 C-a C-c 開啟新的視窗，並同時切換到這個新的視窗

C-a n 或 C-a C-n 或 C-a (space) 切換到下一個視窗（0->1 1->2 ...）

C-a p 或 C-a C-p 切換到上一個視窗（1->0 2->1 ...）

C-a C-a 切換到上一個顯示過的視窗（不是照順序切換）

C-a 0 切換到第 0 個視窗

C-a (1..9) 切換到第 (1..9) 個視窗

C-a w 或 C-a C-w 會列出目前所開啟的視窗

0$ tcsh 1$ tcsh 2*$ tcsh 3$ tcsh

有星號 "*" 的表示目前顯示中的視窗，之後的 tcsh 代表這個視窗的 title ，預設是以開啟時的 shell 名稱

C-a K 關閉所有的視窗並退出 screen

C-a ' 或 C-a " 會出現 "Switch to window:" 字樣，輸入號碼後就可切到該視窗

單一視窗使用中的指令

C-a C 清除目前的視窗內容

When install zylin cdt plugin into eclipse, it will suffer the problem that could not find the"http://www.zylin.com/zylincdt"as below,

After searching, the correct address for installing zylin cdt should change to http://opensource.zylin.com/zylincdt

refer to:

https://jingyan.baidu.com/article/d621e8dae805272865913fa7.html

一、安装

创建安装目录，在/usr/java下建立安装路径，并将文件考到该路径下： 

# mkdir /usr/java

1、jdk-6u11-linux-i586.bin 这个是自解压的文件，在linux上安装如下： 

please go to download jdk-6u11-linux-i586.bin from

http://www.oracle.com/technetwork/java/javase/java-archive-downloads-javase6-419409.html

# chmod 755 jdk-6u11-linux-i586.bin 

# ./jdk-6u11-linux-i586.bin （注意，这个步骤一定要在jdk-6u11-linux-i586.bin所在目录下）

在按提示输入yes后，jdk被解压。

出现一行字：Do you aggree to the above license terms? [yes or no]

Create a image of VMDK file for existing harddisk in ubuntu linux host:

$sudo VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk -rawdisk /dev/sda

if create a image is created from a given partition of physical harddisk, 

$sudo VBoxManage internalcommands createrawvmdk -filename /path/to/file.vmdk -rawdisk /dev/sda -partitions 1,5

Create a image of VMDK file from a exsting harddisk in window host:

1. Run cmd as adminstrator mode 
2. C:\> cd "Program Files\Oracle\VirtualBox"
3. C:\Program Files\Oracle\VirtualBox> VBoxManage internalcommands createrawvmdk -filename "C:\xxx.vmdk" -rawdisk "\\.\PhysicalDrive1"

the "\\.\physicalDrive1" is the harddisk which the image create from.

if create a image is from a given partition of physical harddisk, 

C:\Program Files\Oracle\VirtualBox> VBoxManage internalcommands createrawvmdk -filename "C:\xxx.vmdk" -rawdisk "\\.\PhysicalDrive0" -partitions 6

if need to involve more partitions at once, could add "," between two partitions number, for example, -partitions 6,5

reference from:

https://www.virtualbox.org/manual/ch09.html#idm8266

Installing  VirtualBox Guest Addition in host and target platform still can't chanage window XP resolution, the highest resolution is 1024X768.

Two methods to adjust display resolution.

1.Set vesa resolutions in host platform:

cd c:\programfiles\oracle\virtualbox  
VBoxManage setextradata "VM name" "CustomVideoMode1" "1400x1050x16

2.Configuring the maximum resolution of guests when using the graphical frontend:

VBoxManage setextradata global GUI/MaxGuestResolution any

will remove all limits on guest resolutions.

VBoxManage setextradata global GUI/MaxGuestResolution >width,height<

manually specifies a maximum resolution.

VBoxManage setextradata global GUI/MaxGuestResolution auto

restores the default settings. Note that these settings apply globally to all guest systems, not just to a single machine.

reference from

https://www.virtualbox.org/manual/ch09.html#idm8266

[音響論壇] 調整LP唱盤的八大基本功

1.creat a file.

   dd if=/dev/zero of=/swapfile bs=1024 count=65536

2.make swap file 

    mkswap /swapfile

3.enable swap file

   swapon /swapfile

4.add swap file instance into /etc/fstab for auto enable swap file after reboot.

   /swapfile swap swap defaults 0 0

When meet the problem that can't access the phpmyadmin with "http://xx.xx.xx.xx/phpmyadmin

  the problem could be caused by the following

  1) mysql isn't started up

        --> use this command to up mysql "sudo /etc/init.d/mysql start"

        --> check whether mysql is up or not "mysql -h 127.0.0.1 -P 3306 -u root -p

  2)apache2 dosn't up

        --> to start apache2 with command "sudo /etc/init.d/mysql start" 

  3) phpmyadmin doesn't configure properly

       -->reconfigure it with command "sudo dpkg-reconfigure phpmyadmin"