1 引言

    20世紀90年代后期，嵌入式系統(tǒng)在工業(yè)控制,、遠程監(jiān)控和數(shù)據(jù)采集等領(lǐng)域的應(yīng)用日趨廣泛,，人們對嵌入式系統(tǒng)的存儲容量也提出了較高的要求。因此研制適用于嵌入式系統(tǒng)的大容量,、高速率,、高可靠性的數(shù)據(jù)存儲系統(tǒng)變得日益重要。本文針對一款基于ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" 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title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" 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title="ARM">ARM" title="ARM">ARM" title="ARM">ARM" title="ARM">ARM920T芯片的開發(fā)板,，根據(jù)ATA硬盤接口規(guī)范,，設(shè)計了IDE硬盤接口電路,，實現(xiàn)了對IDE硬盤的讀寫，可以在Linux系統(tǒng)中對其上的文件系統(tǒng)自由訪問,，達到了高速率和高可靠性的要求,。

2 ARM920T與S3C2410介紹

    ARM 包括一系列微處理芯片技術(shù)。ARM920T是ARM系列微處理器的一種,，它采用5階段管道化ARM9TDMI內(nèi)核,，同時配備了Thumb擴展、EmbeddedICE調(diào)試技術(shù)和Harvard總線,。在生產(chǎn)工藝相同的情況下,，性能可達ARM7TDMI芯片的兩倍之多。ARM920T系列主要應(yīng)用于機頂盒產(chǎn)品,、掌上電腦,、筆記本電腦和打印機。

    S3C2410處理器是Samsung 公司基于ARM公司的ARM920T處理器核,，采用0.18umSU造工藝的32位微控制器,。該處理器擁有獨立的16KB指令Cache和16KB數(shù)據(jù)Cache、MMU,、支持TFT的LCD控制器,、NAND閃存控制器、3路UART,、4路DMA,、4路帶PWM的Timer、I/O口,、RTC,、8路10位ADC、TouchScreen接口,、IIC-BuS接口,、IIS-BuS接口、2個USB主機,、1個USB設(shè)備,、SD主機和MMC接口和2路SPI。S3C2410處理器最高可運行在268MHz,。

3 IDE接口及其規(guī)范

    IDE(Integrated Drive Electronics)是從IBM PC/AT上使用的ATA接口發(fā)展而來的,。IDE/ATA磁盤驅(qū)動器與早期的ATA驅(qū)動器相比，增加了任務(wù)文件寄存器,，包括數(shù)據(jù)寄存器,、狀態(tài)寄存器以及反映地址的驅(qū)動器號、磁頭號,、道號和扇區(qū)號寄存器等,。ATA接口規(guī)范定義了信號電纜和電源線的電器特征,、互聯(lián)信號的電器和邏輯特征，還定義了存儲設(shè)備中可操作的寄存器以及命令和協(xié)議,。

3.1 寄存器

    規(guī)范定義了兩組寄存器：命令寄存器和控制寄存器,。命令寄存器用來接收命令和傳送數(shù)據(jù)，控制寄存器用來控制磁盤操作,。常用的寄存器包括數(shù)據(jù)寄存器,、命令寄存器、驅(qū)動器/磁頭寄存器,、柱面號寄存器,、扇區(qū)號寄存器、扇區(qū)數(shù)寄存器和狀態(tài)寄存器,。

3.2 數(shù)據(jù)傳輸方式

    ATA接口規(guī)范定義了兩種數(shù)據(jù)傳輸方式：可編程I/O(PIO)方式和DMA方式,。PIO傳送方式下，CPU對控制器的訪問都是通過PIO進行的,，包括從控制器讀取狀態(tài)信息和錯誤信息,，以及向控制器發(fā)送命令和參數(shù)。在一次PIO數(shù)據(jù)傳輸過程中,，CPU先選址,，然后使讀/寫信號有效，CPU或控制器放數(shù)據(jù)到數(shù)據(jù)總線,，控制器或CPU讀取數(shù)據(jù),，操作完成后，釋放總線,，這樣一次數(shù)據(jù)傳輸完成。DMA方式,，即直接內(nèi)存訪問,，CPU把緩沖區(qū)的地址與需要讀寫的長度告訴外設(shè)，外設(shè)在準備好后向CPU發(fā)出一個DMA請求,，要求CPU暫停使用內(nèi)存,，獲得同意后就直接在內(nèi)存和外設(shè)之間傳輸數(shù)據(jù)，完成后再把對內(nèi)存的訪問權(quán)歸還給CPU,。

4 硬件實現(xiàn)

    如圖1所示,，S3C2410與硬盤之間接口電路分為3個部分：片選信號、數(shù)據(jù)信號和控制信號,。硬盤上寄存器分為兩組,，分別由IDE_CS0和IDE_CS1選中，DA0~DA2則用于組內(nèi)寄存器尋址,；數(shù)據(jù)線DD0~DD15因存在輸入/輸出方向問題,，故用nOE(讀信號)接buffer(74LVTH162245)的DIR引腳來控制緩沖器方向,；控制信號部分因該CPU與硬盤之間DMA時序不一致，故采用一塊EPM7032AETC44-7芯片用于調(diào)整其時序,。PIO模式下,，不需要DMARQ和nDMACK信號，DMA模式下,，這兩個信號才起作用,。

5 軟件實現(xiàn)

    硬盤驅(qū)動程序?qū)崿F(xiàn)分為初始化、打開設(shè)備,、設(shè)備I/O操作和釋放設(shè)備等幾部分,。

5.1 硬盤初始化

    與X86不同，在ARM 體系結(jié)構(gòu)中,，對內(nèi)存和外設(shè)的訪問使用統(tǒng)一的指令,，所以要對外設(shè)地址進行內(nèi)存映射。也就是說,，通過一張表將I/O地址映射到內(nèi)存空間中來,，這部分工作是在系統(tǒng)初始化期間完成的。

    在IDE子系統(tǒng)初始化期間,，Linux系統(tǒng)一旦發(fā)現(xiàn)一個IDE控制器,，就設(shè)置它的ide_hwif_t結(jié)構(gòu)來反映這個控制器和與之相連的磁盤；向Linux的VFS登記每一個控制器,，并分別把它加到blk_dev和blkdevs向量表中,；請求控制適當(dāng)?shù)腎RQ中斷(主IDE控制器是14，次IDE控制器是15)和I/O空間(主控制器0x1f0,，次控制器0x170)：為每一個找到的IDE控制器在gendisk列表中增加一個條目,。

    IDE硬盤的初始化工作由idedisk_init完成：

    (1)在數(shù)組ide_hwifs中找出已登記得各IDE控制器控制的所有IDE硬盤(一個控制器最多控制兩個硬盤)，每個IDE硬盤對應(yīng)一個ide_drive_t結(jié)構(gòu),。

    (2)對找到的每個IDE硬盤,，調(diào)用函數(shù)ide_register_subdriver填寫各IDE硬盤結(jié)構(gòu)中的相關(guān)信息域，主要是填寫其驅(qū)動程序結(jié)構(gòu)ide_driver_t,。硬盤驅(qū)動中的函數(shù)do_rw_disk通過向磁盤控制寄存器寫參數(shù)啟動磁盤操作,，完成真正的數(shù)據(jù)讀寫。

    (3)對找到的每個IDE硬盤,，調(diào)用函數(shù)idedisk_setup進一步設(shè)置其ide_drive_t結(jié)構(gòu),，包括設(shè)置該結(jié)構(gòu)的settings域、doorlocking域,、cyl,、head、sect域、id域等,。

5.2 打開設(shè)備

    打開塊設(shè)備的操作與打開普通文件的操作基本相同,。

    (1)在當(dāng)前進程的文件描述符表中為打開文件找一個空位，申請一塊內(nèi)存,，用于建立新文件的打開文件對象,，即結(jié)構(gòu)file。

    (2)解析設(shè)備特殊文件名,，獲得其VFSinode和dentry結(jié)構(gòu),，根據(jù)dentry結(jié)構(gòu)填寫file結(jié)構(gòu)，尤其是將file結(jié)構(gòu)的f_op域設(shè)為其VFSinode中的缺省文件操作,。

    (3)執(zhí)行該文件操作集中的open操作,，即blkdev_open，它根據(jù)設(shè)備特殊文件的主次設(shè)備號從blkdevs向量表中取出已經(jīng)注冊的文件操作集(file_operations)fops,，用該結(jié)構(gòu)代替file結(jié)構(gòu)中的f_op域,。

    (4)執(zhí)行中新文件操作集中的open操作，即bl帶頭kdev_open,，它根據(jù)VFS

    inode中的i_rdev域查找數(shù)組ide_hwifsp[],，從中找出該IDE硬盤所對應(yīng)的ide_drive_t結(jié)構(gòu)；如果ide_drive_t結(jié)構(gòu)中注冊有驅(qū)動程序,，執(zhí)行驅(qū)動程序集中的open操作,。

    (5)將打開文件對象插入到當(dāng)前進程的文件描述符表中，返回文件描述符,，即打開文件對象在進程文件描述符表中的索引,。

5.3 設(shè)備I/O操作

    讀寫塊設(shè)備時要用到塊緩沖區(qū)(bufer)，對bufer的管理采用BuferCache機制,。它管理bufer的創(chuàng)建,、撤銷、回收,、查找,、更新等，同時還要與系統(tǒng)中的其它部分(如文件系統(tǒng),、內(nèi)存管理等)交互。Linux將Buffer

    Cache從塊設(shè)備驅(qū)動程序中獨立出來,，作為對塊設(shè)備讀寫的通用機制,，所以對塊設(shè)備的讀、寫,、同步等操作采用的都是由操作系統(tǒng)提供的公共函數(shù),，一般為block_read()和block_write()。

    為了減少對塊設(shè)備操作的次數(shù),，讀寫塊設(shè)備時采用延遲操作,，盡量將多個讀寫操作合并,，所以操作請求不是馬上遞交給物理設(shè)備，而是提供了一種手段記錄每次的請求(request),，并為每類塊設(shè)備提供一個請求隊列用來排隊,、合并、重組對該塊設(shè)備的請求,。

    當(dāng)需要從硬盤讀時,，block_read()函數(shù)首先查找Buffer Cache

    如果在其中能找到需要的buffer，則立刻返回：否則,，生成一個讀請求,，并將其加入相應(yīng)的請求隊列排隊。

    當(dāng)需要向硬盤寫時,，block_write()為此次寫操作生成一個buffer,，而后生成一個寫請求，并將其加入相應(yīng)的請求隊列排隊,。

    塊設(shè)備驅(qū)動程序提供了一個請求處理函數(shù),，對硬盤而言是函數(shù)do_rw_disk。在適當(dāng)?shù)臅r候,，硬盤的請求處理函數(shù)啟動,，do_rw_disk處理在請求隊列上排隊的請求，通過向硬盤發(fā)出讀,、寫命令完成對設(shè)備的真正操作,。其偽代碼如下：

DO_RW_DISK(COMMAND)

{

Set_Registers()；

if(COMMAND=READ){

Set read_intr as interrupt process function

Send WIN_READ or WIN_MULTREAD

command to Command register

}

if(COMMAND=WRITE){

Send WIN_WRITE or

WIN_MULTWRITE command to Command register

Get the status of Status register

and set DRQ bit

Set write intr as interrupt process function

Senddatato buferin thedisk

}

}

5.4 釋放設(shè)備

    由設(shè)備驅(qū)動程序中的release操作完成,，一般完成與打開設(shè)備相反的動作：釋放打開設(shè)備特殊文件時在file結(jié)構(gòu)上所創(chuàng)建的私有結(jié)構(gòu),；如果是最后一個設(shè)備的釋放，則從硬件上關(guān)閉設(shè)備,。

6 結(jié)束語

    通過上述方法對IDE硬盤接口的設(shè)計與實現(xiàn),，我們可以在S3C2410開發(fā)板上安全自由地對硬盤上的各種文件系統(tǒng)進行訪問，由于采用DMA方式,，可以滿足用戶對速率的要求,。