查看“DMA”的源代码

== DMA ==
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原文出处：https://help.ubuntu.com/community/DMA

原文作者：UbuntuWiki

授权许可：

翻译人员：韦涛 MillenniumDark

校对人员：leal MillenniumDark bentusi

贡献者：

适用版本：

文章状态：[[等待校对]]

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=== Introduction ===
介绍

If you experience jumpy DVD playback, slow CD ripping, or a general slow down when accessing optical drive(s) it may be because DMA is not enabled. DMA, or Direct Memory Access, lets hard drives and CD/DVD drives access the system memory.

如果你播放DVD时跳桢，CD抓轨很慢，或是存取光存贮器很慢，也许是因为没有开启DMA功能的缘故。DMA(Direct Memory Access)的中文含意是直接内存访问，可以让硬盘和光驱直接存取系统内存数据。

Ubuntu 6.06 (Dapper Drake) has DMA '''automatically''' enabled for drives that support it.

Ubuntu 6.06 (Dapper Drake)能自动为支持的驱动器开启DMA。

attachment:IconsPage/IconDialog-Warning1.png '''Warning:''' Enabling DMA can be dangerous in some cases. Usually issues are directly related to faulty hardware, poorly written drivers, or using settings that are unsupported by your system.

attachment:IconsPage/IconDialog-Warning1.png 警告：开启DMA功能在某些情况下会造成危险。一般来说问题都和下列原因直接相关：有缺陷的硬件、编写质量糟糕的驱动程序，或者使用了你的系统不支持的设置。

'''USING HDPARM INCORRECTLY CAN CAUSE MAJOR DATA CORRUPTION AND/OR LOSS. Most systems newer than 4 years support DMA.'''

不正确的使用HDPARM可以造成存储介质的损坏及/或丢失。最近4年内的系统支持DMA。

=== Enabling DMA ===
开启DMA

To enable DMA, you need to use the <code><nowiki>hdparm</nowiki></code> command and the configuration file <code><nowiki>hdparm.conf</nowiki></code>.

These instructions assume that you are trying to enable DMA on <code><nowiki>hdc</nowiki></code>, usually the CD-rom drive.

为了开启DMA，你需要使用hdparm命令和配置文件hdparm.conf。

这个指导假定你正在尝试开启hdc上的DMA，通常是光盘驱动器。

* See the what the settings are on <code><nowiki>/dev/hdc</nowiki></code>
** 检查/dev/hdc 上的设置
*** 
<pre><nowiki>
sudo hdparm /dev/hdc
</nowiki></pre>
* If you get a line like <code><nowiki> using_dma    =  1 (on)</nowiki></code>, DMA is already enabled. Skip to step 4 to see if it has been enabled at boot time.
** 如果你看到下面的显示： using_dma = 1 (on)，那代表DMA已经开启了。请转至第四步来检测它是否在启动的时候已经开启了。
* Enable DMA on <code><nowiki>/dev/hdc</nowiki></code>
** 开启 /dev/hdc 上的DMA
*** 
<pre><nowiki>
sudo hdparm -d1 /dev/hdc
</nowiki></pre>
* You have now enabled DMA for the drive. However, in order for the settings to be automatically applied at boot there you need to edit the <code><nowiki>/etc/hdparm.conf</nowiki></code> script. To do this use this command:
** 现在你已经为你的驱动器开启了DMA功能。然而，为了在启动的时候让你的设置自动的生效，你需要编辑/etc/hdparm.conf这个文件。使用命令：
*** <code><nowiki>sudo gedit /etc/hdparm.conf</nowiki></code>
Add the following to the end of your hdparm.conf 把下列内容添加到你的hdparm.conf文件中。
*** 
<pre><nowiki>
/dev/hdc {
dma = on
}
</nowiki></pre>
(another way of avoiding editing of the hdparm.conf file is to simply run <code><nowiki>sudo hdparm -d1 -k1 /dev/hdc</nowiki></code> to keep the DMA flag).

FIXME翻译以上部分。

=== Troubleshooting ===
疑难解答

If your drives are configured in [Cable Select] mode and while running <code><nowiki>hdparm</nowiki></code> commands you receive errors related to timeouts or drive not ready, try changing the drive to be a master or slave device depending on your system configuration. This does require opening the case and as far as I know most drives are set to Cable Select from the manufacturer.

Sometimes step 3 above can fail with an "Operation Not Permitted" message. You can fix this by editing the file /etc/modules: For an Intel CPU put the lines

如果你的驱动器配置为 [Cable Select]模式，并且在使用hdparm命令时得到了类似于超时或者驱动没有就绪的错误，那么请尝试根据你的系统配置把驱动器改为主设备或者辅设备。这么做就得打开机箱，并且据我所知，大部分驱动器被生产厂家默认的设置为Cable Select 模式。

有时候上面的第三步会出现“操作不被允许”的错误信息。你可以通过编辑/etc/modules这个文件来修补它。  对于一个英特尔微处理器：  把

<pre><nowiki>
piix
ide-core
</nowiki></pre>
above the line

放在 <code><nowiki>ide-cd</nowiki></code> 之上

For an AMD CPU put the line

对于一个AMD的微处理器：  把 <code><nowiki>amd74xx</nowiki></code> above

放在 <code><nowiki>ide-cd</nowiki></code> 之上

For a VIA Chipset put

对于一个威胜芯片组：  把 <code><nowiki>via82cxxx</nowiki></code> above

放在 <code><nowiki>ide-cd</nowiki></code> 之上

Then reboot and try steps 3-4 again....

然后重新启动系统，重复第三步和第四步

=== Further reading ===
进一步的阅读

The hdparm has further options that may be more risky. They can be seen using the <code><nowiki>man hdparm</nowiki></code> command in the terminal.

FIXME翻译以上部分。

For a detailed description of DMA visit the IEEE

对于详细的DMA描述，请浏览IEEE的网站：

http://standards.ieee.org/reading/ieee/std_public/description/busarch/1212.1-1993_desc.html

IDE, EIDE and UDMA

以及IDE, EIDE and UDMA的网站：

* http://www.spcug.org/reviews/bl0108.htm
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[[category:CategoryDocumentation]]