On the Threat of Metastability in an Asynchronous Fault-Tolerant Clock Generation Scheme
On the Threat of Metastability in an Asynchronous Fault-Tolerant Clock Generation Scheme
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关于异步容错时钟生成方案中亚稳态的威胁
DOI：
10.1109/async.2009.15
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
A. Steininger
中科院分区：
文献类型：
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作者：
Gottfried Fuchs;Matthias Függer;A. Steininger
由于它们基于握手的流控制，异步电路通常不像同步电路那样遭受亚稳态问题。然而，我们将证明，像单事件瞬变这样的故障效应可以迫使（顺序）异步构建块（如Muller C-Elements）进入亚稳态。在容错时钟生成方案的例子中，我们将说明亚稳态可以克服传统的错误遏制边界，并且最终，一个亚稳态颠覆甚至可能导致多个拜占庭容错系统失败。为了量化这种威胁，我们对弹性管道进行了分析建模和仿真，这是我们物理实现容错时钟的核心。我们的分析结果表明，只有一些非常特定宽度的瞬态脉冲可以触发亚稳态行为。因此，即使不考虑其他掩蔽效应，亚稳态翻转通过管道传播的概率也相当小。然而，对于高可靠性应用中使用的电路，必须进行彻底的亚稳态分析。
Due to their handshake-based flow control, asynchronous circuits generally do not suffer from metastability issues as much as synchronous circuits do. We will show, however, that fault effects like single-event transients can force (sequential) asynchronous building blocks such as Muller C-Elements into a metastable state. At the example of a fault-tolerant clock generation scheme, we will illustrate that metastability could overcome conventional error containment boundaries, and that, ultimately, a single metastable upset could cause even a multiple Byzantine fault-tolerant system to fail. In order to quantify this threat, we performed analytic modeling and simulation of the elastic pipelines, which are at the heart of our physical implementation of the fault-tolerant clocks. Our analysis results reveal that only transient pulses of some very specific width can trigger metastable behavior. So even without consideration of other masking effects the probability of a metastable upset to propagate through a pipeline is fairly small. Still, however, a thorough metastability analysis is mandatory for circuits employed in high-dependability applications.