User`s guide

The XMI
2.2.2.3 I/O Address Space
I/O adapter address space consists of ten 32-Mbyte address regions used
to access I/O adapters. See documentation for each XMI adapter to
determine how each implements access through I/O space addressing.
The special case of the XMI-to-VAXBI adapter addresssing is covered in
Section 2.2.2.4.
2.2.2.4 VAXBI Adapter I/O Address Space
Longword-length references directed to a VAXBI’s I/O adapter address
space will be reissued on that VAXBI bus. XMI transactions are translated
into a corresponding VAXBI transaction. The VAXBI address of the
transaction is computed from XMI addresses as E000 0000 + offset or
2000 0000 + offset, where offset is the difference between the XMI address
and the start of the appropriate DWMBB/A module’s address space. XMI
devices can only access VAXBI I/O space, as VAXBI memory space is not
accessible to nodes on the XMI.
To calculate the address of the first register in nodespace (the DTYPE
register):
• The base address of I/O space is E000 0000 (hex, 32-bit addressing) or
2000 0000 (hex, 30-bit addressing).
• D<28:25> correspond to the XMI node number of the I/O adapter.
• D<16:13> correspond to the VAXBI node number if the I/O adapter is
a DWMBB.
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