過去十年來,車載網(wǎng)絡(luò)架構(gòu)變得越來越復(fù)雜。雖然車載網(wǎng)絡(luò)協(xié)議的數(shù)量有所減少,但實(shí)際部署的網(wǎng)絡(luò)數(shù)量卻有顯著增加。這就提出了網(wǎng)絡(luò)架構(gòu)的可縮放性問題,并且要求為滿足各種應(yīng)用和網(wǎng)絡(luò)的實(shí)際需要而優(yōu)化半導(dǎo)體器件?! ?br />
FPGA曾一度被認(rèn)為是僅用于開發(fā)的解決方案,但如今其價(jià)位下降非常迅速,使得許多問題迎刃而解,甚至能以低于傳統(tǒng)ASIC或ASSP解決方案的總體系統(tǒng)成本投產(chǎn)?,F(xiàn)在,面向汽車市場(chǎng)的各大FPGA供應(yīng)商均已通過ISO-TS16949認(rèn)證,使得可編程邏輯器件逐漸成為汽車市場(chǎng)的主流技術(shù)。
車載網(wǎng)絡(luò)電氣架構(gòu)
在過去十年間,很多專用的OEM汽車制造商的網(wǎng)絡(luò)協(xié)議已經(jīng)讓位于CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" 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title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN" title="CAN">CAN、MOST 和 FlexRay等更為標(biāo)準(zhǔn)化的全球協(xié)議。因此,半導(dǎo)體供應(yīng)商可以專心制造符合這些協(xié)議的器件,并使一級(jí)配件供應(yīng)商競(jìng)爭(zhēng)更加激烈并且紛紛降價(jià),同時(shí)也促進(jìn)了汽車OEM制造商之間的模塊互通性。但是,今天的汽車電氣架構(gòu)中仍有許多問題困擾著汽車OEM制造商和一級(jí)配件供應(yīng)商。
工程師可以按幾種不同方式劃分和制定網(wǎng)絡(luò)策略。高端汽車最多可有七條不同網(wǎng)絡(luò)總線同時(shí)運(yùn)行。例如,一輛汽車可以有一條LIN回路用于后視鏡、一條500Kbps的低速CAN回路用于座椅或車門控制等低端功能、一條1Mbps的高速CAN回路用于車身控制、另一條高速CAN回路用于駕駛員信息系統(tǒng)、一條10Mbps的FlexRay回路用來提供實(shí)時(shí)駕駛員輔助數(shù)據(jù),以及一條25Mbps的MOST回路用于在導(dǎo)航或后座娛樂等多種信息娛樂系統(tǒng)內(nèi)部或之間傳輸控制和媒體流。
另一方面,低檔汽車可以只有一條LIN或CAN回路,令所有其他模塊幾乎毫無交互操作地獨(dú)立工作。不同OEM汽車制造商會(huì)以不同方式處理模塊間通信和汽車網(wǎng)絡(luò)拓?fù)浣Y(jié)構(gòu),而且每種車載平臺(tái)都不同,這使一級(jí)配件供應(yīng)商難以開發(fā)既有正確接口又可重復(fù)使用的模塊架構(gòu)。容納模塊的最終架構(gòu)的不確定性正是FPGA的用武之地。
ASIC、ASSP和微控制器具有固定的硬件架構(gòu),其資源往往不是缺乏就是過剩,毫無靈活性可言。FPGA的可編程性(以及可再編程性)便于增減片上通道(如CAN通道),而且允許重復(fù)使用IP。有了這種靈活性,即可將針對(duì)網(wǎng)絡(luò)接口的數(shù)量和類型優(yōu)化過的解決方案迅速制成模塊。
網(wǎng)絡(luò)協(xié)議的半導(dǎo)體實(shí)現(xiàn)
FPGA的長(zhǎng)處不僅在于接口數(shù)量與類型方面的可縮放性。對(duì)ASSP、ASIC和微控制器來說,其外設(shè)宏指令是用硬件實(shí)現(xiàn)的,因此天生就缺少靈活性。而在FPGA環(huán)境中,網(wǎng)絡(luò)接口IP本身可根據(jù)所用IP進(jìn)行優(yōu)化?! ?/p>
例如,利用Xilinx LogiCORE CAN或FlexRay網(wǎng)絡(luò)IP,用戶可以靈活地設(shè)置發(fā)送和接收緩沖器的數(shù)量以及濾波器的數(shù)量。在傳統(tǒng)硬件解決方案中,使用CAN控制器的工程師通常只有16、32和64個(gè)消息緩沖器這三種配置選擇。根據(jù)系統(tǒng)功能的級(jí)別和FPGA外部的可用處理能力,Xilinx的可縮放MOST網(wǎng)絡(luò)接口解決方案包括可配置成主操作或從操作的網(wǎng)絡(luò)控制器IP以及異步采樣速率轉(zhuǎn)換器(ASRC)、數(shù)據(jù)路由器或者復(fù)制保護(hù)用加密引擎等大量IP。
這種IP允許優(yōu)化,既能裝入低端解決方案中的較低密度器件,也能裝入高端解決方案的較高密度器件,并且常常在模塊的目標(biāo)電路板上使用相同的封裝外形。另外,對(duì)于各主要協(xié)議,業(yè)界已開發(fā)出可完善解決方案的中間件堆棧和驅(qū)動(dòng)器。FPGA解決方案的這種可縮放性和通用性在傳統(tǒng)汽車硬件解決方案中是根本不可能實(shí)現(xiàn)的。
各大FPGA供應(yīng)商都有軟微處理器,這些軟微處理器可以在控制功能的架構(gòu)中高效實(shí)現(xiàn),并且其運(yùn)行速度可與某些硬件中嵌入的微處理器媲美。FPGA架構(gòu)的另一大優(yōu)勢(shì)是能夠通過使用乘法器或片上硬MAC中的并行DSP處理功能來卸載微處理器和分區(qū)上的處理任務(wù),從而提高總體性能和吞吐量。
可編程邏輯器件已取得長(zhǎng)足進(jìn)步
可編程邏輯器件已取得長(zhǎng)足進(jìn)步,逐漸成為汽車市場(chǎng)的主流技術(shù)。各種可編程邏輯器件在可靠性方面難分伯仲,而FPGA技術(shù)則可以實(shí)現(xiàn)可縮放的靈活的集成,這在傳統(tǒng)的ASIC、ASSP或微控制器架構(gòu)中是不可能實(shí)現(xiàn)的。開發(fā)周期縮短,可編程邏輯器件供應(yīng)商采用先進(jìn)的工藝技術(shù)以及可編程器件必然帶來的規(guī)模經(jīng)濟(jì),這些均促使總體生產(chǎn)系統(tǒng)成本得以降低?! ?/p>
隨著車載網(wǎng)絡(luò)的關(guān)鍵IP和解決方案日趨成熟以及FPGA架構(gòu)的性能潛力逐漸提高,可編程邏輯器件將在攻克車載電氣架構(gòu)開發(fā)中固有的某些工程難題方面發(fā)揮重要作用。