從電壓分配到平面規劃之多重電壓晶片設計流程

隨著製程進入奈米時代，功率消耗呈現劇烈地成長，因此過度的功率消耗成為晶片設計上之重大挑戰。如果急劇成長的功率消耗現象仍舊不見趨緩，晶片之溫度將會過熱，更進一步，晶片之功能將會失效。為了抑制功率消耗的成長，多重電壓設計﹝multiple-supply voltage design﹞方式因此被提出且被廣泛地應用於動態功率的降低。簡單地說，多重電壓設計是省電與效能之間的取捨；在省電的同時，有可能危害到晶片的效能。因此如何在這之間做取捨，是非常重要的課題。多重電壓設計模式緩和了動態功率的消耗，但，同時，它也帶來許多更嚴苛的晶片設計挑戰，尤其在電壓配置、平面規劃及電源網路合成上。因此，為了處理如此複雜的多重電壓晶片設計，一套完整的設計流程將不可或缺的。在此篇論文中，我們提出一個多重電壓設計流程﹝由電壓配置、平面規劃至電源網路合成與調整﹞，此流程共包含了三大部分：﹝一﹞電壓配置與多重電壓導向之平面規劃、﹝二﹞平面規劃後之電壓島形成、及﹝三﹞平面規劃後之多重電壓導向電源網路的合成。在這系統裡，我們首先發展一個以動態規劃﹝dynamic programming﹞為基礎的電壓分配技術。在符合高效能的要求下，此方法能得到最佳或近似最佳解。在電壓分配步驟之後，我們將產生電壓轉換器，針對於那些需要電壓轉換的連線，這些連線通常連接著不同電壓的電路元件。而後，我們執行電源網路導向的平面規劃，來對多重電壓設計之電路進行平面規劃與擺置的動作。緊接著，我們提出電壓島形成之問題，在此問題裡，我們更深入考慮了電壓轉換器與電源網路規劃之議題。為了解決與處理這問題，我們運用整數線性規劃﹝integer-linear programming﹞技巧來發展數學模式，此模式包含﹝一﹞電壓轉換器考量之連線估計，﹝二﹞電壓島群聚之不等式及﹝三﹞電源網路繞線資源之不等式。又，我們發現先前電源環合成之缺陷，因而發展出新的模組。先前電源環總是被考慮成封住電壓島的「四方形」，但，我們發現，此種假設缺少了實用性，因此，我們將電源環考慮成封住電壓島之「多邊形」。這新的假設將使得電源環之估計更顯精準，且電源環之合成更顯實際。我們提出一套演算法流程，其中包含﹝一﹞快速電壓島之電源環搜尋演算法，與﹝二﹞快速電源環之修整最佳化演算法，以力求電源環之完整性。

關鍵字

實體設計；平面規劃；多重電壓；省電設計；電源網路合成；動態規劃；整數線性規劃；多邊形輪廓搜尋；三維晶片

並列摘要

As the CMOS technology enters the nanometer era, power dissipation is increasing severely and becomes a key challenge in nanometer chip design. If the increasing trend of power dissipation is still not tamed, the temperature of chips may be overheated, and further the functionality of the chips may fail. To moderate the increasing power dissipation, the multiple-supply voltage (MSV) design style recently has been extensively applied to mitigate dynamic-power consumption. Concisely, MSV is a trade-off between power saving and performance; in other words, we may sacrifice the performance whiling conserving the energy. Therefore, how to make a good trade-off becomes a key point for MSV design. MSV lowers supply voltages of non-timing-critical cells for power saving while raising ones of timing-critical cells for performance guarantee. Although the MSV design paradigm mitigates dynamic-power consumption, it brings many crucial design challenges at the same time, especially in voltage assignment, floorplanning, and power-ring synthesis. For such complicated designs, it is desirable to develop a methodology dealing with MSV designs. In this dissertation, we propose an MSV design flow from voltage assignment, through floorplanning, to power-ring synthesis and adjustment. This system consists of three parts: (1) voltage assignment and MSV-aware floorplanning, (2) post-floorplanning voltage-island generation, and (3) MSV-aware post-floorplanning power ring synthesis. In this system, we first propose an effective voltage-assignment technique based on dynamic programming for MSV-aware technology mapping. For circuits without re-convergent fanouts, an optimal solution for the voltage assignment is guaranteed; (that is the power consumption is minimized while the timing constraint is satisfied.) for circuits with re-convergent fanouts, a near-optimal solution is obtained. After the voltage assignment, we then generate a level shifter for each net that connects two blocks in different voltage domains, and perform power-network aware floorplanning for the MSV design. Next, we present a general formulation of the voltage-island generation problem that considers level-shifter planning and power-network routing resources. To tackle the addressed problem, we employ an integer-linear programming (ILP) formulation which consists of (1) level-shifter aware wirelength estimation to capture the timing overhead caused by level shifters, (2) voltage-island-clustering inequalities to avoid complicated constraint transformations, and (3) inequalities to capture the power-network routing-resource usage. Unlike previous works that form the power rings as enclosing bounding boxes of voltage islands, we enable power rings alignment to the outer boundaries of voltage islands. With this new formulation, the power-ring estimation becomes more accurate during floorplanning, and the power-ring synthesis becomes more practical after floorplanning. We therefore propose a linear-time voltage-island power-ring search algorithm to identify the power rings of voltage islands and then present a linear-time optimal power-ring corner-patching algorithm to minimize the number of corners in the power rings by using post-floorplanning whitespaces.

並列關鍵字

physical design ； floorplanning ； multiple-supply voltage ； low-power design ； power-network synthesis ； dynamic programming ； integer-linear programming ； contour searching ； 3D ICs

參考文獻

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[5] J. Chang and M. Pedram, “Energy Minimization Using Multiple Supply Voltages,”

in Proceedings of ACM/IEEE International Symposium on Low Power

國際替代計量

從電壓分配到平面規劃之多重電壓晶片設計流程

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