性能之路: 可互換的8位與32位微處理器
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8位微處理器市場仍在振蕩，因為8位機價格、功耗以及代碼高效的優(yōu)勢，每天都會有新的應用。但是對更高級的應用，市場壓力不斷提升性能需求及內存容量。例如，家用型產品需要用到變速電機控制，這就要求更高性能更大存儲的32位設備。8位微處理器片上flash存儲器最多到128KB，而最新的一些32位嵌入式處理器則擁有3MB大小的閃存，提供更多編程空間處理復雜的控制算法。
半導體廠商嘗試幫助開發(fā)者向32位設備轉變，獲取更高性能。低檔32位微處理器與高檔8位微處理器價格相當，因此單位成本不是阻礙。真實的費用來源于轉變過程本身，包括確保多年的經驗能夠保留。在投資中，開發(fā)工具占了很重要的角色。
8位和32位微處理器的外圍提供類似功能，但是實際功能性和用戶可用的程序模塊很可能不同。開發(fā)者必須重寫與芯外設備連接的低端設備驅動。
工程師必須解決設計差異，比如中斷能力、默認變量長度以及內存中地址的分配。同樣，任何一個定時循環(huán)也有可能重新改寫。
無論32位開發(fā)工具多么簡單和容易使用，對新開發(fā)者而言都需要繼續(xù)學習來掌握。
性能及內存的要求會迫使開發(fā)者從8位到32位微處理器轉變，但是他們必須面對上市時間延遲和開發(fā)費用增加的挑戰(zhàn)。新替代方案是重新設計32位微處理器無論在外形還是在功能上都更接近8位微處理器。同樣的外圍設備、輸出引腳以及單一開發(fā)工具套件裝置，既適合8位也適合32位微處理器，產生真正管教兼容的32位設備來替代8位產品。
想要轉向32位微處理器的設計者面對許多的挑戰(zhàn)，現(xiàn)在能在芯片設計層面處理好。例如，典型8位設備可能只有一個信號調試接口，而典型32位設備需要很多接口。重新設計32位的接口使其成為一個引腳可以大大提高兼容性從而降低了開發(fā)者的工作難度。
我們的最終目標是8位與32位微處理器使用同樣的封裝、同樣的開發(fā)板以及同樣的開發(fā)工具。評估板插槽上的8位的設備替換為32位設備，重新編譯代碼，就擁有一個32位的系統(tǒng)。這就是我們Freescale的方向。而更高性能的另一個方法是8位到32位控制器合為一體，展現(xiàn)出大部分吸引人的替代——這是從前沒有嘗試過的。
轉向32位性能呈上升勢頭。無論選用了哪種設備和開發(fā)工具，優(yōu)勢在那些花更少時間開發(fā)而更多時間推銷新32位微處理器應用上。
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 it's 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-spe
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
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 developer's 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.
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