XCV400E-6PQG240I_xilinxbootloader本文導(dǎo)讀：前一時刻經(jīng)過的狀態(tài)( 如圖中，Sig n，=小路徑上前一時刻狀態(tài)為T 否則為T。如果存貯了L 個時刻的25位狀態(tài)幸存比特，就可以從當(dāng)前時刻的某一狀態(tài)開始回溯L 時刻得到對應(yīng)的小路徑起始狀態(tài)( 如圖中從S 狀態(tài)回溯L 時刻得到初始的P 狀態(tài))。實際上無論從當(dāng)前的何種狀態(tài)開始回溯，當(dāng)回溯深度L 為5～1倍的編碼寄存器數(shù)時.
就要使用主控制器的I/O口通過軟件來模擬，這就在很大程度上限制了其應(yīng)用給數(shù)據(jù)傳輸帶來不便。在FPGA技術(shù)迅速發(fā)展的時代，解決這個問題方便的辦法就是集成一個SPI核到芯片上。這據(jù)業(yè)界通用的SPI總線的標(biāo)準(zhǔn)，設(shè)計一種可復(fù)用的高速SPI總線。設(shè)計過程中很多變量都采用參數(shù)形式，具體應(yīng)用于工程實踐時根據(jù)實際需要更改參數(shù)即可。
XCV400E-6PQG240I_xilinxbootloader每6個時鐘開始時，回溯讀出的起始狀態(tài)設(shè)為而譯碼讀出的初始狀態(tài)為上一個6個時鐘結(jié)束時回溯得到的初始狀態(tài)( 虛線箭頭所示)。每6個時鐘開始的時候，雙端口BlockRam 的個讀寫地址的初始值按照圖示的規(guī)律循環(huán)右移，且前進(jìn)的方向每6個時鐘反向一次。到64×個時鐘后恢復(fù)初始的地址值和方向。由圖中可以看出，64×個時鐘后。
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