Specifications

Data Structures
1.7 Channel Request Block (CRB)
Table 1–9 (Cont.) Contents of Interrupt Transfer Vector Block (VEC)
Field Name Contents
VEC$W_MAPALT The following bits are defined within VEC$W_MAPALT:
VEC$V_MAPALT Number of first Q22–bus alternate map register
allocated to driver that owns controller data
channel.
IOC$REQALTMAP writes this field when the
routine allocates a set of Q22–bus alternate map
registers to a driver fork process for a DMA
transfer. IOC$RELMAPREG reads the field to
deallocate a set of map registers.
Device drivers read this 15-bit field in calculating
the starting address of a MicroVAX Q22–bus
transfer that uses a set of alternate map registers.
VEC$V_ALTLOCK Alternate map register set is permanently
allocated (when set).
VEC$W_NUMALT Number of Q22–bus alternate map registers allocated to driver.
IOC$REQALTMAP writes this field when allocating a set of alternate map
registers. IOC$RELMAPREG reads this field to deallocate a set of alternate
map registers.
1–33