1、Serial RapidIO協(xié)議解析1. 物理層特性1.1 Two transmitters(short run and long run) and a single receiver are specified for each of three baudrates, 1.25, 2.50, and 3.125 GBaud.1.2 The short run transmitter should be used mainly for chip-to-chip connections on either the same printed circuit board or across a si

2、ngle connector.1.3 The long run transmitter specifications use larger voltage swings that are capable of driving signals across backplanes. This allows a user to drive signals across two connectors and a backplane.1.4 The most common equalization techniques that can be used Pre-emphasis on the trans

3、mitter A passive high pass filter network placed at the receiver. This is often referred to as passive equalization. The use of active circuits in the receiver. This is often referred to as adaptive equalization.2. 信號定義2Signal pin descriptions for a RapidIO 1x/4x LP-Serial port. The interface is def

4、ined either as a single- or four-lane, full duplex, point-to-point interface using differential signaling. A single-lane implementation consists of 4 wires and a four-lane implementation consists of 16 wires.3. Electrical Specifications33.1 Short Run Transmitter Specifications2.5 GBaud、3.125 GBaud特性

5、與1.25GBaud Short Run Transmitter AC Timing Specifications基本相同，區(qū)別在于：2.5 GBaud UI 400ps3.125 GBaud UI 320ps3.2 Long Run Transmitter Specifications2.5 GBaud、3.125 GBaud特性與1.25GBaud Long Run Transmitter AC Timing Specifications基本相同，區(qū)別在于：2.5 GBaud UI 400ps3.125 GBaud UI 320ps3.3 Receiver Specifications2.

6、5 GBaud、3.125 GBaud特性與1.25GBaud Receiver Specifications基本相同，區(qū)別在于：2.5 GBaud UI 400ps3.125 GBaud UI 320ps4. 10G級互連技術比較 協(xié)議類型軟件實現(xiàn)TCP/IP 協(xié)議棧的以太網(wǎng)4x PCI Express4x SRIO備注軟件開銷高中低 SRIO 協(xié)議棧簡單，一般都由硬件實現(xiàn)，軟件開銷很小硬件糾錯重傳不支持支持 支持  傳輸模式消息DMADMA，消息  拓撲結構任意 PCI樹任意 SRIO支持直接點對點或通過交換器件實現(xiàn)的各種拓撲結構直接點對點對等互連支持 不支持

7、支持 SRIO互連雙方可對等的發(fā)起傳輸。傳輸距離長 中中SRIO針對嵌入式設備內(nèi)部互連，傳輸距離一般小于1米數(shù)據(jù)包最大有效載荷長度1500字節(jié)4096字節(jié) 256字節(jié)嵌入式通信系統(tǒng)對實時性要求高，SRIO小包傳輸可減少傳輸時延打包效率 (以傳輸256字節(jié)數(shù)據(jù)為例)79% (TCP包)82%9296%打包效率是有效載荷長度與總包長的比率。SRIO支持多種高效包格式。5. 幀結構l ACKID：向Packet發(fā)送端響應Packet接收確認信息；l RSVD：保留域；l PRIO：Packet優(yōu)先級；l TT：器件ID長度；l Ftype：Logi_Inf的格式類型；l Dest_Addr：目的器件

8、ID號；l Src_Addr：源器件ID號；l Logi_Inf：邏輯層信息，包括數(shù)據(jù)長度、數(shù)據(jù)位置、郵箱號等；l Payload：數(shù)據(jù)凈核；l CRC：采用多項式X16+X12+X5+1生成16bit CRC碼；6. 協(xié)議結構RapidIO協(xié)議定義了3個層：邏輯層、傳輸層和物理層。12345677.1 邏輯層邏輯層定義了操作協(xié)議和相應的包格式。RapidIO支持的邏輯層業(yè)務主要是：直接IO/DMA （Direct IO/Direct Memory Access）和消息傳遞（Message Passing）。l 直接IO/DMA直接IO/DMA模式的前提是主設備知道被訪問端的存儲器映射。主設備

9、可以直接讀寫從設備的存儲器。直接IO/DMA在被訪問端的功能往往完全由硬件實現(xiàn)，被訪問的器件無任何軟件負擔。對上層應用來說，發(fā)起直接IO/DMA傳輸主要需提供以下參數(shù)：目地器件ID、數(shù)據(jù)長度、數(shù)據(jù)在目地器件存儲器中的位置。直接IO/DMA模式又可進一步分為以下幾種傳輸格式：NWRITE: 寫操作，不要求接收端響應。 NWRITE_R: 帶響應的NWRITE（NWRITE with Response），要求接收端響應。 SWRITE：流寫（Stream Write），數(shù)據(jù)長度必須是8字節(jié)的整數(shù)倍，不要求接收端響應。 NREAD: 讀操作。 l 消息傳遞消息傳遞（Message Passing）模

10、式則類似于以太網(wǎng)的傳輸方式，它不要求主設備知道被訪問設備的存儲器狀況。數(shù)據(jù)在被訪問設備中的位置則由郵箱號（類似于以太網(wǎng)協(xié)議中的端口號）確定。從設備根據(jù)接收到的包的郵箱號把數(shù)據(jù)保存到對應的緩沖區(qū)，這一過程無法完全由硬件實現(xiàn)，而需要軟件協(xié)助。對上層應用來說，發(fā)起消息傳遞主要需提供以下參數(shù)：目地器件ID、數(shù)據(jù)長度、郵箱號。7.2 傳輸層RapidIO是基于包交換的互連技術，傳輸層定義了包交換的路由和尋址機制。RapidIO網(wǎng)絡主要由兩種器件，終端器件（End Point）和交換器件（Switch）組成。終端器件是數(shù)據(jù)包的源或目的地，不同的終端器件以器件ID來區(qū)分。RapidIO支持8 bits 或

11、16 bits器件ID，因此一個RapidIO網(wǎng)絡最多可容納256或65536個終端器件。與以太網(wǎng)類似，RapidIO也支持廣播或組播，每個終端器件除了獨有的器件ID外，還可配置廣播或組播ID。交換器件根據(jù)包的目地器件ID進行包的轉發(fā)，交換器件本身沒有器件ID。RapidIO的互連拓撲結構非常靈活，除了通過交換器件外，兩個終端器件也可直接互連。7.3 物理層RapidIO 1.x 協(xié)議定義了1x/4x SRIO協(xié)議，具體參照1-3節(jié)。7. 錯誤檢測和恢復機制SRIO協(xié)議采用錯誤檢測和重發(fā)機制對發(fā)送數(shù)據(jù)進行保護和恢復，重傳糾錯的功能由物理層完成。協(xié)議規(guī)定，每個數(shù)據(jù)包的傳輸需得到接收端的確認，并在

12、發(fā)送端為每個傳輸?shù)臄?shù)據(jù)包保留備份，直至收到一個數(shù)據(jù)包接收確認或發(fā)送端口確定該數(shù)據(jù)包遇到不可恢復的錯誤。協(xié)議可檢測以下4種錯誤：l An idle sequence errorl A control symbol errorl A packet errorl A time-out waiting for an acknowledgment control symbol88.1 Idle sequence error空閑碼由A、K、R字符組成，輸入端檢測到無效的字符或有效字符但不是A、K、R字符時，進入Error-stopped recovery process。8.2 Control symbo

13、l error協(xié)議可檢測以下2種symbol error：l An uncorrupted control symbol that violates the link protocoll A corrupted control symbolLink protocol violations include the following: Unexpected packet-accepted, packet-retry, or packet-not-accepted control symbol Packet acknowledgment control symbol with an unexpec

14、ted packet_ackID value Link time-out while waiting for an acknowledgment control symbolInput ports detect the following types of control symbol corruption. A control symbol containing invalid characters or valid but non-data characters A control symbol with an incorrect CRC value8.3 Packet ErrorsInp

15、ut ports detect the following types of packet corruption Packet with an unexpected ackID value Packet with an incorrect CRC value Packet containing invalid characters or valid non-data characters Packet that overruns defined boundary such as the max payload.8.4 Time-out waiting等待確認信號的鏈接超時作為違反鏈接協(xié)議的情況處理，參照8.2節(jié)。8. 參考標準l RapidIOTM Interconnect Specification P