The four 32-bit Initialization Vector Value registers INTVECTVx set the 128-bit
Initialization Vector Value data block that is used by some modes of operation
as an additional initial input. INTVECTV0.INTVECTV corresponds to the first word
of the Initialization Vector Value, INTVECTV3.INTVECTV to the last one. These
registers are write-only to prevent the Initialization Vector Value from being
read by another application. For CBC, OFB and CFB modes, the Initialization
Vector Value corresponds to the initialization vector value. or CTR mode, it
corresponds to the counter value.