请香主帮看下!!!

只看该作者 · 2009-8-26 19:17

if (errorstatus == SD_OK)
  {
/* SD CARD */
/* Send ACMD41 SD_APP_OP_COND with Argument 0x80100000 */
                                          //0x40000000
while ((!validvoltage) && (count < SD_MAX_VOLT_TRIAL))
{
   /* SEND CMD55 APP_CMD with RCA as 0 */
   SDIO_CmdInitStructure.SDIO_Argument = 0x00;
   SDIO_CmdInitStructure.SDIO_CmdIndex = SDIO_APP_CMD;
   SDIO_CmdInitStructure.SDIO_Response = SDIO_Response_Short;
   SDIO_CmdInitStructure.SDIO_Wait = SDIO_Wait_No;
   SDIO_CmdInitStructure.SDIO_CPSM = SDIO_CPSM_Enable;
   SDIO_SendCommand(&SDIO_CmdInitStructure);
   errorstatus = CmdResp1Error(SDIO_APP_CMD);
   if (errorstatus != SD_OK)
   {
      return(errorstatus);
   }
   SDIO_CmdInitStructure.SDIO_Argument = SD_VOLTAGE_WINDOW_SD | SDType;
   SDIO_CmdInitStructure.SDIO_CmdIndex = SDIO_SD_APP_OP_COND;
   SDIO_CmdInitStructure.SDIO_Response = SDIO_Response_Short;
   SDIO_CmdInitStructure.SDIO_Wait = SDIO_Wait_No;
   SDIO_CmdInitStructure.SDIO_CPSM = SDIO_CPSM_Enable;
   SDIO_SendCommand(&SDIO_CmdInitStructure);
   errorstatus = CmdResp3Error();
   if (errorstatus != SD_OK)
   {
      return(errorstatus);
   }
   response = SDIO_GetResponse(SDIO_RESP1);
   validvoltage = (bool) (((response >> 31) == 1) ? 1 : 0);
   count++;
}
if (count >= SD_MAX_VOLT_TRIAL)
{
   errorstatus = SD_INVALID_VOLTRANGE;
   return(errorstatus);
}
if (response &= SD_HIGH_CAPACITY)
{
   CardType = SDIO_HIGH_CAPACITY_SD_CARD;
}
  }/* else MMC Card */
  return(errorstatus);
}

这是万利399元STM32开发板中关于SDIO BUS操作SD卡的例子中的一段代码，但是有点不明白，
发送 ACMD41命令，回复应是R3  "errorstatus = CmdResp3Error();
"但后面有是“response = SDIO_GetResponse(SDIO_RESP1);”有点不理解。
还有就是为什么要“while ((!validvoltage) && (count < SD_MAX_VOLT_TRIAL))”

请香主帮我解释下，谢谢了！！

香主辛苦了！