VMEbus Master Interface
6-15
6.3 VMEbus Master Interface
The architecture of the Universe can be described in terms of three channels: the
PCI bus channel, the DMA channel, and the interrupt channel. The Universe
functions as the VMEbus master interface upon the request of any of these chan-
nels, with the interrupt channel having the highest priority. The VMEbus master
supports Read-Modify-Write (RMW) and Address-Only-with-Handshake (ADOH).
A PCI master can lock VME resources via the VMEbus Lock command in the
ADOH cycle. The Universe does not support RETRY* as a termination from the
VMEbus slave.
The VOWN bit in the Universe’s MAST_CLT register sets VMEbus ownership (see
Register Map 6-3). The CWT bits in the Universe’s LMISC register at hex offset
184
16
affect the performance of the PCI bus and, indirectly, the VMEbus.
SUPER
Supervisor/user AM code.
Binary 00=reserved, 01=non-privileged, 10=supervisor, 11=both.
VAS
VMEbus address space.
Binary 000=A16, 001=A24, 010=A32, 011=reserved, 100=reserved,
101=CR/CSR, 110=user1, 111=user2.
LD64EN
Enable 64-bit PCI transactions.
Binary 0=disabled, 1=enabled.
LLRMW
Allow VMEbus to lock PCI bus during RMW. For improved performance,
disable this feature until it is needed.
Binary 0=disabled, 1=enabled.
LAS
PCI bus memory space. (power-up option)
Binary 00=memory space, 01=I/O space, 10=PCI configuration space,
11=reserved.
31
30
29
28
27
26
25
24
Reserved
CWT (unused)
Register Map 6-7. Universe PCI Miscellaneous, LMISC
Содержание BajaPPC-750
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