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為什麼acer n10跑的比兩年前的ipaq 3600還嫚阿??

cgr
個人積分：40分
文章編號：104261

40分

21樓

2004-01-25 1:38

ghosty wrote:
"ARM" 是智慧財產, 分為好幾個版本, 把智慧財產賣給其他公司, 可能會因需求加入
不同I/O介面, 所以各家的ARM CPU並不相同, 但是核心指令是一樣的. 據我所知,
Strong ARM 主要是根據ARM4版本指令集改過來的, XScale是ARM5, 但是卻不
支援浮點運算(只有定點運算).

sigh..沒有浮點運算我的工作量增加了不少T_T
BTW 最近在寫arm assembler, 不太清楚thumb instruction有什麼優點..有沒有哪位大哥可為小弟介紹?

cgr

cgr
個人積分：40分
文章編號：104263

40分

22樓

2004-01-25 1:51

自問自答:o..

Q4. What is Thumb?

A4 Thumb is a 16-bit extension to ARM's 32 bit instruction set. It enables writing of 16-bit instructions for an ARM micro. The 16-bit instructions are decompressed in to comparable 32-bit ARM instructions during processing.

There are some major advantages to Thumb. Thumb code gets better code density that 32-bit ARM code. Thus there is memory saving and less power consumption with Thumb. It also enables ARM/Thumb MCUs to run efficiently from an external 16-bit data bus thus reducing the price of the LSI by reducing external bus size. When instructions are being fetched from an external 16-bit bus, Thumb code is more efficient and gets better performance results.

Q6. How does ARM code compare to Thumb code?

A6 The following is a general comparison of ARM-code vs. Thumb-code solutions: » Thumb code requires 70% of the space of the ARM code
» Thumb code uses 40% more instructions than the ARM code
» With 32-bit memory, the ARM code is 40% faster than the Thumb code
» With 16-bit memory, the Thumb code is 45% faster than the ARM code
» Thumb code uses 30% less external memory power than ARM code
Therefore Thumb code has a higher density and uses less power. Thumb gives better performance when running off of 16-bit wide memory whereas ARM code gives better performance when running off of 32-bit wide memory.

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