Arduino DUE Base Functionality

Projects Interfacing w/ Software on the Computer
2

It's defined in sam3x8e.h#L46-L55 or similar files as simple as

#if !(defined(__ASSEMBLY__) || defined(__IAR_SYSTEMS_ASM__))
#include <stdint.h>
#ifndef __cplusplus
typedef volatile const uint32_t RoReg; /**< Read only 32-bit register (volatile const unsigned int) */
#else
typedef volatile       uint32_t RoReg; /**< Read only 32-bit register (volatile const unsigned int) */
#endif
typedef volatile       uint32_t WoReg; /**< Write only 32-bit register (volatile unsigned int) */
typedef volatile       uint32_t RwReg; /**< Read-Write 32-bit register (volatile unsigned int) */
#endif