Specifications

Accessing Device Interface Registers

Note

In register access discussions, the term control and status register

(CSR) is sometimes used instead of the generic term interface register.

In this manual, the terms are equivalent.

2.1 Mapping I/O Device Registers

Unlike OpenVMS VAX systems (where the operating system maps device register

space into the processors’ virtual address space) before you access device registers

on OpenVMS AXP systems, you must map the registers into the processor’s

virtual address space. OpenVMS AXP provides the IOC$MAP_IO routine, which

allows a caller to request mapping based on device characteristics without regard

to the platform hardware implementation of I/O space access.

Note

systems, and IOC$READ_IO and IOC$WRITE_IO are not supported. If

you are porting an OpenVMS VAX XMI device driver to an OpenVMS

AXP system, you must use CRAMs.

Once your device is mapped, you can access it using a CRAM data structure and

associated routines, or the IOC$READ_IO and IOC$WRITE_IO routines.

2.2 Platform Independent I/O Bus Mapping

The platform independent I/O bus mapping routine is called IOC$MAP_IO. This

routine maps I/O bus physical address space into an address region accessible

by the processor. The caller of this routine can express the mapping request in

terms of the bus address space without regard to address swizzling, dense space,

sparse space. IOC$MAP_IO is supported on PCI, EISA, TURBochannel, and

Futurebus+. It is not supported on XMI.

In additon to IOC$MAP_IO, the following platform independent mapping and

access routines exist:

• IOC$READ_IO

• IOC$WRITE_IO

• IOC$UNMAP_IO

The IOC$MAP_IO routine maps I/O bus physical address space into an address

region accessible by the processor. The IOC$UNMAP_IO routine is provided to

unmap a previously mapped space. IOC$READ_IO and IOC$WRITE_IO are I/O

access routines that provide a platform independent way to read and write I/O

space without the overhead of CRAM allocation and initialization. These routines

require that the I/O space that is to be accessed have been previously mapped by

a call to IOC$MAP_IO. For more information about these routines, see OpenVMS

AXP Device Support: Reference.

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