AVR Freaks

Please keep this to one thread.

Moderator

(locked to avoid cross posts).

EDIT unlocked temporarily to say you can see this in iotn817.h:

/* Two-Wire Interface */
typedef struct TWI_struct
{
    register8_t CTRLA;  /* Control A */
    register8_t reserved_0x01;
    register8_t DBGCTRL;  /* Debug Control Register */
    register8_t MCTRLA;  /* Master Control A */
    register8_t MCTRLB;  /* Master Control B */
    register8_t MSTATUS;  /* Master Status */
    register8_t MBAUD;  /* Master Baurd Rate Control */
    register8_t MADDR;  /* Master Address */
    register8_t MDATA;  /* Master Data */
    register8_t SCTRLA;  /* Slave Control A */
    register8_t SCTRLB;  /* Slave Control B */
    register8_t SSTATUS;  /* Slave Status */
    register8_t SADDR;  /* Slave Address */
    register8_t SDATA;  /* Slave Data */
    register8_t SADDRMASK;  /* Slave Address Mask */
    register8_t reserved_0x0F;
} TWI_t;

and then later:

#define TWI0                  (*(TWI_t *) 0x0810) /* Two-Wire Interface */

So things like TWI0.MCTRLA should be accessible.

This is just standard C - you should have been able to get that from reading the .h file.