问题 单项选择题

以下关于嵌入式系统开发的叙述,正确的是______。

A.宿主机与目标机之间只需要建立逻辑连接
B.宿主机与目标机之间只能采用串口通信方式
C.在宿主机上必须采用交叉编译器来生成目标机的可执行代码
D.调试器与被调试程序必须安装在同一台机器上

答案

参考答案:C

解析:在嵌入式系统开发过程中,有三种不同的开发模式,这三种开发模式就会涉及本题所述的宿主机与目标机(调试程序运行的机器称为宿主机,被调试程序运行的机器称为目标机)。下面将详细说明这三种开发模式。
本机开发:本机开发也就是在目标机(在嵌入式系统中通常把嵌入式系统或设备简称为目标机)中直接进行操作系统移植及应用程序的开发。在这种方式下进行开发,首先就得在目标机中安装操作系统,并且具有良好的人机开发界面。
交叉开发:意思就是在一台宿主机(在嵌入式系统中通常把通用PC称为宿主机)上进行操作系统的裁剪,以及编写应用程序,在宿主机上应用交叉编译环境编译内核及应用程序,然后把目标代码下载到目标机上运行。这就需要在宿主机上安装、配置交叉编译环境(交叉开发工具链),使其能够编译成在目标机上运行的目标代码。
模拟开发:建立在交叉开发环境基础之上。除了宿主机和目标机以外,还得提供一个在宿主机上模拟目标机的环境,使得开发好的内核和程序直接在这个环境下运行以验证其正确性,这就不需要将每次的修改都下载到目标机中,待程序正确后再下载到目标机上运行。这样就可以达到在没有目标机的情况下调试软件的目的。比较著名的模拟开发环境有SkyEye,它能够模拟如ARM等处理器的开发环境。模拟硬件环境是一项比较复杂的工程,所以多数商业嵌入式系统的开发采用的是交叉开发模式。
从以上解释可以看出,宿主机与目标机可能在一台机器上,也可能在不同机器上。宿主机与目标机之间既要有逻辑连接,还要有物理连接。至于通信方式,串口只是其中一种标准,还可采用其他方式。

选择题
单项选择题

With U.S. companies sitting on an estimated $1.8 trillion in cash, it raises the question: Why aren’t they deploying more of their hoard to expand their businesses Or one might channel John Maynard Keynes to ask: Where have the "animal spirits" gone Although capital spending in the U.S. is up 12 percent since the lows of early 2009, it’s still running $88 billion below the peak of $1.34 trillion reached in the first quarter of 2008, says Joseph LaVorgna, chief U.S. economist at Deutsche Bank. He doesn’t expect capital spending to catch up to that peak level and officially start to expand until the second quarter of 2011. (LaVorgna’s definition of capital spending includes physical equipment and software, but not structures such as new stores or manufacturing plants. Spending on structures is about 2 percent of gross domestic product, one-third the size of capital sending’s contribution to GDP, he says.)

"The trend and momentum have definitely turned and it’s just a matter of time before you see other companies give way to capital spending, and eventually that will result in hiring," says LaVorgna. But with spending running $88 billion below peak, he says employment "should be farther along than it is." Companies that have built up a lot of cash are starting to take some chances such as expanding into new markets, which requires hiring new workers, says John Challenger, chief executive officer of Challenger, Gray & Christmas, an employment consulting firm. U.S. companies have announced the hiring of 118,209 new employees through August, according to data collected by the firm.

So who’s stepping up to the plate Some companies refuse to be cowed and are taking big, if calculated, chances, including ambitious capital projects, hiring new workers, and expanded investment in research and development, according to growth-oriented mutual fund managers contacted by Businessweek.com. If there’s a common denominator, it’s a perceived opportunity and confidence in sustainable demand, whether due to new trends in technology or to new markets that need certain products. Other names came from a list of the top-hiring U.S. companies through July 2010 compiled by Challenger, Gray & Christmas.

"We don’t spend capital unless we have a new contract to supply oxygen, nitrogen, or hydrogen to our customers," says James Sawyer, Praxair’s chief financial officer. "Those are 15-year contracts with minimal take-or-pay clauses written into them, which ensure we will get a good return on our capital investment, regardless of how the rest of the economy is doing."

Some younger outfits with entrepreneurial managers who have lived through a few business cycles think their companies may be able to steal a march on competitors more reluctant to spend, says Aram Green, manager of Clear Bridge Advisors Small Cap Growth Fund. "There’s clearly been a decision by management that ’This is not the time to take our foot off the accelerator. In fact, it’s time to push harder and further distance our product from the competition.’\

Which of the following could best summarize the passage ?()

A.Capital spending will result in hiring.

B.New stores or manufacturing plants come up.

C.How can companies benefit from capital spending.

D.Companies give way to capital spending.