at91_sdcard源码分析(3)

SD_MCI_Init函数做的工作是初始化SD卡。有可能是SD卡或是MMC卡。

//------------------------------------------------------------------------------/// Run the SDcard SD Mode initialization sequence. This function runs the     根据SD协议初始化SD卡（或MMC卡），此函数完成后进入数据传输模式/// initialisation procedure and the identification process, then it sets the/// SD card in transfer state to set the block length and the bus width./// Returns 0 if successful; otherwise returns an SD_ERROR code./// \param pSd  Pointer to a SD card driver instance./// \param pSdDriver  Pointer to SD driver already initialized//------------------------------------------------------------------------------unsigned char SD_MCI_Init(SdCard *pSd, SdDriver *pSdDriver){    unsigned int sdCid[4];    unsigned char isCCSet;    unsigned char error;    unsigned int status;    unsigned char cmd8Retries = 2;    unsigned char cmd1Retries = 100;    // The command GO_IDLE_STATE (CMD0) is the software reset command and sets card into Idle State    // regardless of the current card state.    error = Cmd0(pSd);　　//软件复位    if (error) {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    // CMD8 is newly added in the Physical Layer Specification Version 2.00 to support multiple voltage    // ranges and used to check whether the card supports supplied voltage. The version 2.00 host shall    // issue CMD8 and verify voltage before card initialization.    // The host that does not support CMD8 shall supply high voltage range...  检查是否支持CMD8命令    TRACE_DEBUG("Cmd8()\n\r");    do {        error = Cmd8(pSd, 1);    }    while ((error == SD_ERROR_NORESPONSE) && (cmd8Retries-- > 0));    if (error == SD_ERROR_NORESPONSE) {  //不支持CMD8命令，所以SD卡的版本是2.00以下，或者它不是SD卡或MMC卡。        // No response : Ver2.00 or later SD Memory Card(voltage mismatch)        // or Ver1.X SD Memory Card        // or not SD Memory Card        TRACE_DEBUG("No response to Cmd8\n\r");        // ACMD41 is a synchronization command used to negotiate the operation voltage range and to poll the        // cards until they are out of their power-up sequence.        error = Acmd41(pSd, 0, &isCCSet);  //发送ACMD41命令        if (error) {            // Acmd41 failed : MMC card or unknown card  不支持ACMD41，它可能是MMC卡，下面先复位再发送CMD1命令偿试初始化MMC卡            error = Cmd0(pSd);            if (error) {                TRACE_ERROR("Error during initialization (%d)\n\r", error);                return error;            }            do {                error = Cmd1(pSd);            }            while ((error) && (cmd1Retries-- > 0));            if (error) {                TRACE_ERROR("Error during initialization (%d)\n\r", error);                return error;            }            else {                TRACE_DEBUG("CARD MMC\n\r");                pSd->cardType = CARD_MMC;            }        }        else {            if(isCCSet == 0) {                TRACE_DEBUG("CARD SD\n\r");                pSd->cardType = CARD_SD;            }        }    }    else if (!error) {   //发送CMD8命令成功，那么它是版本2.00以上的SD卡。         // Valid response : Ver2.00 or later SD Memory Card        error = Acmd41(pSd, 1, &isCCSet);        if (error) {            TRACE_ERROR("Error during initialization (%d)\n\r", error);            return error;        }        if (isCCSet) {            TRACE_DEBUG("CARD SDHC\n\r");            pSd->cardType = CARD_SDHC;        }        else {            TRACE_DEBUG("CARD SD\n\r");            pSd->cardType = CARD_SD;        }    }    else {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    // The host then issues the command ALL_SEND_CID (CMD2) to the card to get its unique card identification (CID) number.    // Card that is unidentified (i.e. which is in Ready State) sends its CID number as the response (on the CMD line).    error = Cmd2(pSd, sdCid);    //获取CID寄存器的内容。    if (error) {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    // Thereafter, the host issues CMD3 (SEND_RELATIVE_ADDR) asks the    // card to publish a new relative card address (RCA), which is shorter than CID and which is used to    // address the card in the future data transfer mode. Once the RCA is received the card state changes to    // the Stand-by State. At this point, if the host wants to assign another RCA number, it can ask the card to    // publish a new number by sending another CMD3 command to the card. The last published RCA is the    // actual RCA number of the card.    error = Cmd3(pSd);     if (error) {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    // The host issues SEND_CSD (CMD9) to obtain the Card Specific Data (CSD register),    // e.g. block length, card storage capacity, etc...    error = Cmd9(pSd);    if (error) {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    // At this stage the Initialization and identification process is achieved    // The SD card is supposed to be in Stand-by State    do {        error = Cmd13(pSd, &status);        if (error) {            TRACE_ERROR("Error during initialization (%d)\n\r", error);            return error;        }    }    while ((status & STATUS_READY_FOR_DATA) == 0);    // If the 4 bit bus transfer is supported switch to this mode  选择当前的SD卡或MMC卡，使它进入数据传输模式。    // Select the current SD, goto transfer state     error = Cmd7(pSd, pSd->cardAddress);    if (error) {        TRACE_ERROR("Error during initialization (%d)\n\r", error);        return error;    }    if (pSd->cardType != CARD_MMC) {     //如果是SD卡，那么设置成4位数据线模式。        // Switch to 4 bits bus width (All SD Card shall support 1-bit, 4 bitswidth        error = Acmd6(pSd, 4);        if (error) {            TRACE_ERROR("Error during initialization (%d)\n\r", error);            return error;        }    }    else {        MCI_SetBusWidth((Mci *)pSdDriver, MCI_SDCBUS_1BIT);    }    return 0;}