AWR1843: VIM Capture Event Sources

Dear TI-Team,

i am facing the following issue:

I can't select the correct capture event for the RTI module. I am trying to write 0x09 to the VIM CAPEVTSRC register, but it didn't work, i am using the following structure to access the register:

/*** VIM Capture Event Source Register; offset=78h ***/
typedef union {
  uint32 Word;
  struct {
    uint8 CAPEVETSRC0          :7;        /* Capture event source 0 mapping control */
    uint16 RESERVED0            :9;        /* RESERVED */
    uint8 CAPEVETSRC1	     :7;        /* Capture event source 1 mapping control */
    uint16 RESERVED1            :9;        /* RESERVED */
  } Bits;
} VIMCAPEVTSTR;
extern volatile VIMCAPEVTSTR           _VIMCAPEVT REG_ADDRESS(VIMCAPEVT_ADDR);	//maps the union to address of vim capture event source register
#define VIMCAPEVT                              _VIMCAPEVT.Word
#define VIMCAPEVT_SRC0                 _VIMCAPEVT.Bits.CAPEVETSRC0
#define VIMCAPEVT_SRC1                 _VIMCAPEVT.Bits.CAPEVETSRC1

Write to the register:

VIMCAPEVT_SRC0 = 0x09U;
VIMCAPEVT = 0x09U; //tried also

After a write attempt the CAPEVTSRC still contains 0x00. The processor operates in privileged mode.

Is a precondition needed to write to this register, that is not mentioned in the data sheet? How can i select the desired capture event?

Regards,

Sergej