Everything will be fine ::

준비중 :-)

my story 2012/01/29 14:43

포트폴리오 중심으로 블로그를 개편할 예정입니다. 그동안 포스팅 했던 내용들은 전부 비공개 처리했습니다. :-)

Posted by besapius

with or without MMU, (기록용)

references/hello! world 2010/10/29 17:19

http://www.mjmwired.net/kernel/Documentation/nommu-mmap.txt

http://www.linuxjournal.com/article/7221
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Without VM, each process must be located at a place in memory where it can be run. In the simplest case, this area of memory must be contiguous. Generally, it cannot be expanded as there may be other processes above and below it. This means that a process in uClinux cannot increase the size of its available memory at runtime as a traditional Linux process would.

Without VM, swap is effectively impossible, although this limitation is rarely an issue on the kinds of systems that run uClinux. They often do not have hard drives or enough memory to make swap worthwhile.
--
http://linux.derkeiler.com/Newsgroups/comp.os.linux.embedded/2008-02/msg00022.html

There are three common uses that I can think of for (v)fork from "normal" applications. One is in forking servers, another other is for executing external subtasks, and the third is for splitting a task into parallel executed parts.

In the first case, things like webservers will often fork new processes to handle incoming connections. In this situation, it must be a real fork, since the new process keeps the same code and inherits things like file handles from the parent. This is a traditional unix server arrangement, and does not work well under ucLinux or windows ("fork" in *nix is extremely efficient using COW, but very slow if you don't have an MMU and must copy everything, or if the OS simply doesn't support the concept). Such servers need to be heavily modified to work without fork - they need to either use select() and other such asynchronous techniques, or they must use threads instead of processes. (Modern apache, for example, uses a mixture of forks and threads.)

For applications that fork off external subtasks, you normally see a fork/exec pair, often connected by a pipe to the parent. This sort of structure is normally fairly easily modified to a vfork.

For applications that use fork to parallise (is that a word?) their execution (keeping the same binary, but with different processes executing different parts of the code), it is probably better to re-write using threads. Traditionally, *nix was bad at thread handling - there was no standardisation, and it was very unclear how threads relate to processes for scheduling). Since fork was so cheap on *nix, there was no real need for threads - unlike on windows, where fork is expensive so threads were needed. But modern linux and ucLinux handle threads well, making it a good choice in many situations.
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기록용

Posted by besapius

TAG Linux, MMU, Real-time kernel, Real-Time OS, RTLinux, RTOS, uClinux

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HTML 5

references/hello! world 2010/07/07 13:38

참 공부할 것도 많고 궁금한 것도 많고
이런 저런 이유로 현재까지는 학교에 남아 있을 생각은 눈꼽 만큼도 없지만,
이런 저런 이유를 넘어설 만큼 궁금한게 많아서 가끔 학교에 남아서 계속 공부를 할까라는 생각이 들기도 한다.

어쨌든 HTML5가 계속 표준화 작업 중이긴 하지만 몇몇 브라우저에서 지원을 한다니
미리 살펴보지 않을 수가 없네 :-P

HTML5 태그

New Markup Elements

New elements for better structure:

Tag	Description
<article>	For external content, like text from a news-article, blog, forum, or any other content from an external source
<aside>	For content aside from the content it is placed in. The aside content should be related to the surrounding content
<command>	A button, or a radiobutton, or a checkbox
<details>	For describing details about a document, or parts of a document
<summary>	A caption, or summary, inside the details element
<figure>	For grouping a section of stand-alone content, could be a video
<figcaption>	The caption of the figure section
<footer>	For a footer of a document or section, could include the name of the author, the date of the document, contact information, or copyright information
<header>	For an introduction of a document or section, could include navigation
<hgroup>	For a section of headings, using <h1> to <h6>, where the largest is the main heading of the section, and the others are sub-headings
<mark>	For text that should be highlighted
<meter>	For a measurement, used only if the maximum and minimum values are known
<nav>	For a section of navigation
<progress>	The state of a work in progress
<ruby>	For ruby annotation (Chinese notes or characters)
<rt>	For explanation of the ruby annotation
<rp>	What to show browsers that do not support the ruby element
<section>	For a section in a document. Such as chapters, headers, footers, or any other sections of the document
<time>	For defining a time or a date, or both

New Media Elements

HTML 5 provides a new standard for media content:

Tag	Description
<audio>	For multimedia content, sounds, music or other audio streams
<video>	For video content, such as a movie clip or other video streams
<source>	For media resources for media elements, defined inside video or audio elements
<embed>	For embedded content, such as a plug-in

The Canvas Element

The canvas element uses JavaScript to make drawings on a web page.

Tag	Description
<canvas>	For making graphics with a script

New Form Elements

HTML5 offers more form elements, with more functionality:

Tag	Description
<datalist>	A list of options for input values
<keygen>	Generate keys to authenticate users
<output>	For different types of output, such as output written by a script

New Input Type Attribute Values

Also, the input element's type attribute has many new values, for better input control before sending it to the server:

Type	Description
tel	The input value is of type telephone number
search	The input field is a search field
url	The input value is a URL
email	The input value is one or more email addresses
datetime	The input value is a date and/or time
date	The input value is a date
month	The input value is a month
week	The input value is a week
time	The input value is of type time
datetime-local	The input value is a local date/time
number	The input value is a number
range	The input value is a number in a given range
color	The input value is a hexadecimal color, like #FF8800