随着科技的迅猛发展，嵌入式系统开发者承受了巨大的压力。由于市场日益复杂的应用需求，开发者们经常面对着微处理器性能不足的状况，于是不得不将目光投向性能更好的微处理器。如今，使用4位微处理器的开发者都在寻找划算的8位微处理器替代；而用8位的开发者则转向兼容DSC（数字信号控制器）和32位的选择。造成这种状况的原因有很多，而日益增长的内存容量以及在同样价位微处理器性能的不断提高更进一步加剧的这种趋势。
8位微处理器市场仍在振荡，因为8位机价格、功耗以及代码高效的优势，每天都会有新的应用。但是对更高级的应用，市场压力不断提升性能需求及内存容量。例如，家用型产品需要用到变速电机控制，这就要求更高性能更大存储的32位设备。8位微处理器片上flash存储器最多到128KB，而最新的一些32位嵌入式处理器则拥有3MB大小的闪存，提供更多编程空间处理复杂的控制算法。
半导体厂商尝试帮助开发者向32位设备转变，获取更高性能。低档32位微处理器与高档8位微处理器价格相当，因此单位成本不是阻碍。真实的费用来源于转变过程本身，包括确保多年的经验能够保留。在投资中，开发工具占了很重要的角色。
32位微处理工具天生就比8位微处理器更加复杂和昂贵。芯片制造者及其团队始终为简化32位开发工具组件和降低基本评估板价格到$500以下而工作。然而，开发者仍忙于大量芯片的结构差异。例如：
8位和32位微处理器的外围提供类似功能，但是实际功能性和用户可用的程序模块很可能不同。开发者必须重写与芯外设备连接的低端设备驱动。
工程师必须解决设计差异，比如中断能力、默认变量长度以及内存中地址的分配。同样，任何一个定时循环也有可能重新改写。
无论32位开发工具多么简单和容易使用，对新开发者而言都需要继续学习来掌握。
性能及内存的要求会迫使开发者从8位到32位微处理器转变，但是他们必须面对上市时间延迟和开发费用增加的挑战。新替代方案是重新设计32位微处理器无论在外形还是在功能上都更接近8位微处理器。同样的外围设备、输出引脚以及单一开发工具套件装置，既适合8位也适合32位微处理器，产生真正管教兼容的32位设备来替代8位产品。
想要转向32位微处理器的设计者面对许多的挑战，现在能在芯片设计层面处理好。例如，典型8位设备可能只有一个信号调试接口，而典型32位设备需要很多接口。重新设计32位的接口使其成为一个引脚可以大大提高兼容性从而降低了开发者的工作难度。
我们的最终目标是8位与32位微处理器使用同样的封装、同样的开发板以及同样的开发工具。评估板插槽上的8位的设备替换为32位设备，重新编译代码，就拥有一个32位的系统。这就是我们Freescale的方向。而更高性能的另一个方法是8位到32位控制器合为一体，展现出大部分吸引人的替代——这是从前没有尝试过的。
转向32位性能呈上升势头。无论选用了哪种设备和开发工具，优势在那些花更少时间开发而更多时间推销新32位微处理器应用上。
英文原文：
The path to performance: Interchangeable 8- and 32-bit mICrocontrollers
The ultimate goal is to develop 8- and 32-bit MCUs that share the same socket, the same board, and the same tools.
By Mike MCCourt, Freescale SEMIconductor -- EDN, 2/14/2007
Technology races forward, and its putting a lot of pressure on embedded-system developers. Competing in markets with increasingly complex applications, developers often face performance shortfalls that cause them to turn to increasingly higher-performance microcontrollers. Developers using 4-bit devices today are looking for cost-effective 8-bit aLTErnatives, and 8-bit users are turning to compatible DSC (digital signal controller) and 32-bit options. There are many reasons for this migration, which is being further enabLED by products with increased memory caPACities and improved performance at comparable price levels.
The 8-bit market remains vibrant, with many new applications being unearthed daily that take advantage of the price, power, and code-efficiency benefits of 8-bit microcontrollers. But for advanced applications, market pressures are driving up performance needs and memory sizes. For example, household appliances are now using variable-speed motor control, which requires the higher performance and larger memories of 32-bit devices. On-Chip flash memory for 8-bit microcontrollers generally maxes out at 128 k bytes, whereas some of the latest 32-bit embedded processors integrate as much as 3 Mbytes of flash, providing more programming headroom to handle sophisticated control algorithms.
Semiconductor manufacturers are trying to help developers transition to 32-bit devices by easing the migration to higher performance. Low-end 32-bit microcontrollers are priced comparably with high-end 8-bit devices, so unit cost is less of a roadbLOCk. The real expense comes in the transition process itself, including making sure that years of previous experience are retained. Development tools play a major role in this investment.
32-bit development tools are inherently more complex and more expensive than 8-bit tools. Chipmakers and their partners have been working to simplify their 32-bit tool suites and reduce the cost for basic evaluation boards to less than $500. However, developers must still address a number of architectural differences between chips. For example:
Peripherals on 8- and 32-bit devices may provide similar functions, but the exact functionality and user-visibility programming models will likely be different. Developers will need to rewrite and reverify lower-level device drivers that interface to the on-chip peripheral hardware.
Engineers must address architectural differences, such as interrupt capabilities and default variable sizes and their layout in memory. Also, any timing loops will probably require rewriting.
No matter how simple and easy-to-use the 32-bit tools are, they often require an extended learning curve for new developers to master.
Performance and memory requirements may force developers to migrate from 8-bit to 32-bit microcontrollers, but the challenges they then face CAN lead to time-to-market delays and increased development costs. A novel alternative is to redesign a 32-bit microcontroller to look and act more like an 8-bit device. Identical peripherals and PIN-outs and a single tool set suitable for both 8- and 32-bit devices can produce a 32-bit device thats a true pin-compatible, drop-in replacement for an 8-bit product.
Many of the challenges facing designers who want to migrate to 32-bit now can be dealt with at the chip-design level. For instance, a typical 8-bit device may have only a single-pin debugging interface, while a 32-bit device typically requires many more pins. Remapping the 32-bit interface to one pin can greatly enhance compatibility and make the developers job easier.
The ultimate goal is to develop 8- and 32-bit microcontrollers that share the same socket, the same board, and the same tools. You can take the 8-bit part out of your evaluation-board socket, drop in the 32-bit part, recompile the code, and have a functional 32-bit system. This is the direction we are taking at Freescale. While other paths to higher performance exist, our 8- to 32-bit controller continuum shows great promise as the most attractive alternative—one that has never been tried before.
The migration to 32-bit performance is gaining momentum. Regardless of which devices and tools developers choose, the advantage goes to those who spend less time developing and more time selling their new 32-bit applications.
英文原文地址： http://www.edn.com/article/CA6415134.html
来源： http://article.ednchina.com/CPUDSP/200707231100581.htm
本文关键字：微处理器 ARM单片机，单片机-工控设备 - ARM单片机
