降低傳送次數之窄匯流排編碼

Abstract

窄匯流排是指寬度比資料寬度要小的匯流排，而和資料寬度等寬的匯流排則稱一般匯流排，這篇論文將針對使用8-bit寬的匯流排來傳送32-bit寬的資料的環境，使用窄匯流排可以節省晶片面積但是卻需要較多的傳送次數，大部分著重面積考量的系統希望能使用窄匯流排卻無法容忍效能和額外能量的損失，我新增了些功能給傳送端和接收端以減少在窄匯流排上的傳送次數，針對不同的資訊流，我將提出不同的方法，在指令位址流上，我使用T0-C以利用其連續的特性而使用NBDAT去利用其不連續的特性，在資料位址流上，我使用variable stride algorithm、historical address algorithm和SRWEC (Separated Read/Write Encoding Contents) 的概念，在指令流上，我使用指令壓縮的技巧來減少傳送次數，在資料流上，我使用SRWEC和一些減少資料大小的概念以減少傳送次數，在我的環境下，一筆資料若不編碼將需要四次傳送，因此，我的編碼的最低傳送次數比例是25%，我將儘可能將傳送次數減少至25%，如此一來，將有更多系統會願意使用窄匯流排。

Narrow Bus is a Bus with narrower width than data width. The Bus with the same width with data width is called normal Bus. This thesis will focus on 8-bit width Bus and 32-bit width data environment. Using narrow Bus can save chip area but the Bus transactions will be raised. Most area constraint systems hope to use narrow Bus but they cannot tolerate the performance loss and extra system static energy consumption caused by additional Bus transactions. I add some functions to the transmitter and corresponding receiver to reduce Bus transactions on narrow Bus. I will adopt suitable coding methods to the proposed transmitter depending on the stream type. In instruction address stream, I use T0-C to utilize the sequential property and narrow Bus DAT to utilize the branch behavior property. In data address stream, variable stride algorithm, historical addresses algorithm and the idea of SRWEC (Separated Read/Write Encoding Contents) are used. In instruction stream, a code compression algorithm is used to reduce the instruction size. In data stream, the idea of SRWEC, the occurrence of small value and the relationship between data are utilized. The number of narrow Bus transaction is four times of the number of normal Bus transactions. In other words, the Bus transactions of normal Bus are 25% of the Bus transactions of narrow Bus without coding. I hope to reduce the number of narrow Bus transactions of streams as close to 25% as possible so that the extra Bus transactions overhead is slighter and there will be more systems are willing to use narrow Bus.