嵌入式系統時常利用草稿型記憶體來替代快取，因為草稿型記憶體可以讓程式在運作中變得比較容易被預測。即時系統需要可預先預測執行時間，因為它們必須安排程式在特定的時間點完成。而這個特定的時間點必須大於每個程式的最差執行時間
我們實驗室繼續針對草稿型記憶體配置做研究，主要是為了讓我們的草稿型記憶體配置能夠減少每一個程式的最差執行時間。比較我們先前的結果，這篇論文主要是改善我們的記憶體模組、記憶體配置演算法、支援最差即時系統和測量基準測試程式和平台。
這篇論文主要是:1)首次將真正的最差執行時間測量加入到我們草稿型記憶體配置中，2)我們些微的改善了之前草稿型記憶體的效能，3)並且大大提高了我們草稿型記憶體的適用性，並且利用擴展的方法來支援遞迴的程式。

Real-time systems often use SPM instead of cache, because SPM allows a program’s run time to be more predictable. Real-time system need predictable runtimes, because they must schedule programs to finish within specific deadlines. A deadline should be larger than its program’s worst-case execution time (WCET).
Our laboratory is conducting ongoing research into scratchpad memory allocation (SPM) for reducing the WCET of a program. Compared to our previous work, this current thesis improves our memory model, our allocation algorithms, our real-time support, and our measurement benchmarks and platform.
Our key accomplishments in this paper are to: 1) add, for the first time in the literature, true WCETmeas analysis to an SPM allocator, 2) to modestly improve the performance of our previous allocator, and 3) to greatly increase the applicability over that allocator, by extending the method to support recursive programs.

Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Improvements in Comparison to Our Previous Allocator . . . . . . . . 3
1.2 Improvements in Comparison to Other SPM Allocators . . . . . . . . . 3
2. Background Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Memory Access Costs in Modern Embedded Systems . . . . . . . . . . 5
2.2 Measuring the Worst-Case Execution Time (WCET) . . . . . . . . . . 10
2.2.1 Measurement-Based Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Static Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.3 What the Differences between Measurement and Static
Analysis Mean for Our SPM Allocator . . . . . . . . . . . . . . . . . . 14
2.3: Memory Operations on the ARM Processor . . . . . . . . . . . . . . . . . 17
3. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1: SPM Allocation to Improve the ACET . . . . . . . . . . . . . . . . . . . . . 19
3.2 General Compiler Methods to Improve the WCET . . . . . . . . . . . . 21
3.3 WCET-aware SPM allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.1 Our Group’s Previous WCET-Aware Allocator . . . . . . . . . . . . 24
4. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1 Fixing the Technical Difficulties of [3] . . . . . . . . . . . . . . . . . . . . . 26
4.2 Adding Support for PC-Relative Variables . . . . . . . . . . . . . . . . . . 28
4.3 Using a Realistic Memory Model in the Allocator . . . . . . . . . . . 28
4.4 Adding Support to Minimize DRAM Misses . . . . . . . . . . . . . . . . 29
4.5 Adding Support for Recursive Programs . . . . . . . . . . . . . . . . . . 32
5. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2. Performance Improvements to Our Previous Work . . . . . . . . . . . 37
5.2.1 Discussion of Specific Benchmarks . . . . . . . . . . . . . . . . . . . . 40
5.3. Applicability Improvements to Our Previous Work . . . . . . . . . 42
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

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[22] The MiBench Suite. http://www.eecs.umich.edu/mibench/

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