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Explorer
Explorer
147 次查看
注册日期: ‎02-14-2019

跨时钟域的clockskew

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请问在跨时钟域的时序约束中,什么时候不需要考虑clockskew? 什么时候不需要考虑holdtime? 必须要考虑的是什么?

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Moderator
Moderator
94 次查看
注册日期: ‎11-05-2010

回复: 跨时钟域的clockskew

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Hi, @victor_dotouch ,

Clockskew在setup 和hold time分析中都有. Hold time 分析主要是计算clockskew和datapath 的差异.

考虑Clockskew的前提是:

  1. 源时钟和目的时钟之前的有有效的相位关系

  2. 设计中ClockSkew是tool 有能力处理的. (Ex: clockskew=3ns 对tool来说就无法自动完成hold violation的修复, n要通过逻辑控制来保证数据传输的正确性) 

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2 条回复2
122 次查看
注册日期: ‎01-22-2015

回复: 跨时钟域的clockskew

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@victor_dotouch 

A clock domain crossing(CDC) of data can occur between either synchronous or asynchronous clock domains.

When the clock domains are synchronous, a direct CDC of the data is sometimes possible. Vivado timing analysis will tell you if this direct crossing of data is possible. Thus, clock skew, hold time and other things are important for the direct crossing.

When the clock domains are asynchronous, a circuit called a synchronizer must be used to send data through the CDC.  See XPM_CDC_HANDSHAKE in UG953 for an example of a synchronizer.  Timing analysis will analyze parts of the synchronizer. Hold time and clock-to-data skew are important for this analysis.  However, clock-to-clock skew is not important for asynchronous CDCs.

Mark

Moderator
Moderator
95 次查看
注册日期: ‎11-05-2010

回复: 跨时钟域的clockskew

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Hi, @victor_dotouch ,

Clockskew在setup 和hold time分析中都有. Hold time 分析主要是计算clockskew和datapath 的差异.

考虑Clockskew的前提是:

  1. 源时钟和目的时钟之前的有有效的相位关系

  2. 设计中ClockSkew是tool 有能力处理的. (Ex: clockskew=3ns 对tool来说就无法自动完成hold violation的修复, n要通过逻辑控制来保证数据传输的正确性) 

-------------------------------------------------------------------------
Don't forget to reply, kudo, and accept as solution.
-------------------------------------------------------------------------