个人初学者，实在不懂为什么有些数据结构的域要加__IO比如这个 [mw_shl_code=c,true]typedef struct { __IO uint8_t CSDStruct; /*!< CSD structure */ __IO uint8_t SysSpecVersion; /*!< System specification version */ __IO uint8_t Reserved1; /*!< Reserved */ __IO uint8_t TAAC; /*!< Data read access-time 1 */ __IO uint8_t NSAC; /*!< Data read access-time 2 in CLK cycles */ __IO uint8_t MaxBusClkFrec; /*!< Max. bus clock frequency */ __IO uint16_t CardComdClasses; /*!< Card command classes */ __IO uint8_t RdBlockLen; /*!< Max. read data block length */ __IO uint8_t PartBlockRead; /*!< Partial blocks for read allowed */ __IO uint8_t WrBlockMisalign; /*!< Write block misalignment */ __IO uint8_t RdBlockMisalign; /*!< Read block misalignment */ __IO uint8_t DSRImpl; /*!< DSR implemented */ __IO uint8_t Reserved2; /*!< Reserved */ __IO uint32_t DeviceSize; /*!< Device Size */ __IO uint8_t MaxRdCurrentVDDMin; /*!< Max. read current @ VDD min */ __IO uint8_t MaxRdCurrentVDDMax; /*!< Max. read current @ VDD max */ __IO uint8_t MaxWrCurrentVDDMin; /*!< Max. write current @ VDD min */ __IO uint8_t MaxWrCurrentVDDMax; /*!< Max. write current @ VDD max */ __IO uint8_t DeviceSizeMul; /*!< Device size multiplier */ __IO uint8_t EraseGrSize; /*!< Erase group size */ __IO uint8_t EraseGrMul; /*!< Erase group size multiplier */ __IO uint8_t WrProtectGrSize; /*!< Write protect group size */ __IO uint8_t WrProtectGrEnable; /*!< Write protect group enable */ __IO uint8_t ManDeflECC; /*!< Manufacturer default ECC */ __IO uint8_t WrSpeedFact; /*!< Write speed factor */ __IO uint8_t MaxWrBlockLen; /*!< Max. write data block length */ __IO uint8_t WriteBlockPaPartial; /*!< Partial blocks for write allowed */ __IO uint8_t Reserved3; /*!< Reserded */ __IO uint8_t ContentProtectAppli; /*!< Content protection application */ __IO uint8_t FileFormatGrouop; /*!< File format group */ __IO uint8_t CopyFlag; /*!< Copy flag (OTP) */ __IO uint8_t PermWrProtect; /*!< Permanent write protection */ __IO uint8_t TempWrProtect; /*!< Temporary write protection */ __IO uint8_t FileFormat; /*!< File Format */ __IO uint8_t ECC; /*!< ECC code */ __IO uint8_t CSD_CRC; /*!< CSD CRC */ __IO uint8_t Reserved4; /*!< always 1*/ } SD_CSD; /** * @brief Card Identification Data: CID Register */ typedef struct { __IO uint8_t ManufacturerID; /*!< ManufacturerID */ __IO uint16_t OEM_AppliID; /*!< OEM/Application ID */ __IO uint32_t ProdName1; /*!< Product Name part1 */ __IO uint8_t ProdName2; /*!< Product Name part2*/ __IO uint8_t ProdRev; /*!< Product Revision */ __IO uint32_t ProdSN; /*!< Product Serial Number */ __IO uint8_t Reserved1; /*!< Reserved1 */ __IO uint16_t ManufactDate; /*!< Manufacturing Date */ __IO uint8_t CID_CRC; /*!< CID CRC */ __IO uint8_t Reserved2; /*!< always 1 */ } SD_CID;[/mw_shl_code] 为什么它们前面都加了关键字__IO