1 引言

隨著半導(dǎo)體工藝的發(fā)展,，片上系統(tǒng)SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" 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title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" 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title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC" title="SOC">SOC已成為當(dāng)今一種主流技術(shù)?；贗P復(fù)用的SOC設(shè)計(jì)是通過用戶自定義邏輯(UDL)和連線將IP核整合為一個(gè)系統(tǒng),，提高了設(shè)計(jì)效率，加快了設(shè)計(jì)過程,，縮短了產(chǎn)品上市時(shí)間,。但是隨著設(shè)計(jì)規(guī)模的增大，集成密度的提高,，IP引腳的增多,，IP的植入深度加大必然使得測試驗(yàn)證工作繁重。據(jù)統(tǒng)計(jì),，在SOC設(shè)計(jì)中,，各種內(nèi)核的測試驗(yàn)證工作所用的時(shí)間占整個(gè)設(shè)計(jì)過程的60％～80％，SOC及IP核的測試驗(yàn)證已成為SOC技術(shù)發(fā)展的瓶頸,。如何在最短的時(shí)間內(nèi)高效迅速地通過IP核驗(yàn)證與測試．并把其集成在SOC中成為業(yè)界關(guān)注的焦點(diǎn)和研究領(lǐng)域急待突破與實(shí)現(xiàn)的方向,。

基于IP核復(fù)用的SOC，其IP核類型和來源都不相同,，即使已驗(yàn)證好的IP核在集成時(shí)也不能確保不出差錯(cuò),。IP核被集成到SOC后，其輸入輸出端口也嵌入到SOC,，原本可測的端口失去了原有的可控性和可觀測性,，變得不可測。

因此人們一直尋求有效的測試驗(yàn)證技術(shù),。本文給出了基于內(nèi)建自測試方法(BIST),，在設(shè)計(jì)編譯碼器IP核的同時(shí)，考慮其測試外殼設(shè)計(jì),，以期提高IP核可測性,。

2 測試結(jié)構(gòu)

所謂測試，就是在被測電路的輸入引腳施加相應(yīng)的激勵(lì)信號(hào),，然后檢測輸出引腳的響應(yīng),，并將檢測的輸出引腳的響應(yīng)與期望引腳的響應(yīng)進(jìn)行比較以判斷電路是否存在故障的過程。

IP核測試的目的在于檢測IP核是否存在功能和時(shí)序錯(cuò)誤,，從而對(duì)IP核進(jìn)行修改,，提高產(chǎn)品的可靠性。一般采用訪問,、隔離,、控制的手段對(duì)IP核的輸入端施加激勵(lì)來得到響應(yīng)與期望的響應(yīng)進(jìn)行比較。嵌入式IP核的測試結(jié)構(gòu)如圖1所示,。

測試激勵(lì)源為嵌入式IP核生成測試所需的激勵(lì),。響應(yīng)分析器對(duì)所得到的響應(yīng)進(jìn)行分析,，如果相同則表明沒有故障，不同則表明存在故障,。測試訪問機(jī)制是 SOC傳送數(shù)據(jù)的一種手段,，它將測試激勵(lì)傳送到IP核的輸入端口并將測試響應(yīng)從IP核的輸出端口傳送到響應(yīng)分析器。測試外殼是IP核同訪問機(jī)制及器件其他邏輯之間的接口,；測試外殼以實(shí)現(xiàn)片上核與核之間的測試隔離,，也可以為IP核提供了測試數(shù)據(jù)傳送通道。

3 內(nèi)建自測試原理

內(nèi)建自測試是可測性設(shè)計(jì)的一種重要方法,。其基本思想是讓電路自己生成測試向量,，而非通過外部施加測試向量，并且依靠自身判斷所得到的結(jié)果是否正確,。內(nèi)建自測試原理圖如圖2所示,。

其中測試外殼(wrapper)在IP核的設(shè)計(jì)之中就予以考慮。通過測試外殼外部可以控制BIST和正常模式的切換,。測試外殼內(nèi)部多采用邊界掃描模塊,、移位寄存器或多路訪問器等，它起到訪問,、隔離,、控制的作用，可提高IP核的可測性,。然而加入測試外殼會(huì)使IP核的面積開銷增大,，因此必須在IP核的可測性和面積之間進(jìn)行權(quán)衡。

4 內(nèi)建自測試的實(shí)現(xiàn)

可控性指驅(qū)動(dòng)一個(gè)節(jié)點(diǎn)為邏輯狀態(tài)0或1的難易程度,；可觀測性指從外部端口觀察內(nèi)部節(jié)點(diǎn)故障的難易程度,；可測性就是指在整個(gè)電路全部節(jié)點(diǎn)的可控性和可觀測性。很顯然,，高可測性比較容易產(chǎn)生測試向量并且測試效果良好。

為了提高IP核的可測性,，在IP核的設(shè)計(jì)中就考慮了設(shè)計(jì)特定電路方便測試,。以BIST實(shí)現(xiàn)IP核的測試，一般具有如下優(yōu)勢：簡化測試接口,；改善測試質(zhì)量,；降低測試成本；提高測試可靠性,。

基于BIST的編譯碼器IP核測試實(shí)現(xiàn)框圖如圖3所示,。

　　通過測試外殼控制輸入/輸出寄存器將編譯碼器隔離使它們互不影響，正常狀態(tài)和測試狀態(tài)能夠切換,，提高了IP核的可測性,。具體的實(shí)現(xiàn)過程如下：

(1)正常狀態(tài)下原始碼輸入編碼器,，由其輸出的碼再進(jìn)入譯碼器又轉(zhuǎn)換為原始碼；

(2)測試狀態(tài)下測試外殼的測試向量輸入編碼器,，由其輸出的碼直接進(jìn)入譯碼器,，由譯碼器輸出的碼為測試響應(yīng)輸出，使其與期望值比較,；圖3中的模式選擇模塊的邏輯結(jié)構(gòu)如圖4所示,。


圖4中mod為模式選擇控制端，置0為正常狀態(tài),。當(dāng)rood為1時(shí),，out_sel輸入測試向量，再由in_tem輸出,，進(jìn)入in_sel,；當(dāng)mod 為0時(shí)，cod_out輸出片外,，從而實(shí)現(xiàn)了正常狀態(tài)和測試狀態(tài)的切換,。可以用硬件描述語言編寫此邏輯電路,。用VHDL描述如下：

此模式選擇模塊實(shí)現(xiàn)狀態(tài)之間的切換,，電路簡單，易于實(shí)現(xiàn),。

5 結(jié)束語

BIST為嵌入式內(nèi)核的測試提供了一個(gè)可解決的方案,，其測試效果明顯，故障覆蓋率較高,，實(shí)現(xiàn)簡單,。通過加入測試外殼可以實(shí)現(xiàn)對(duì)IP核的訪問、隔離,、控制,，有效地提高了IP核的可測性。但是采用BIST會(huì)使電路面積增加額外開銷,，必須在IP核的可測性和面積之間進(jìn)行權(quán)衡,。