0
IOSPACE I/O space indicator. Read as one;
write operations have no effect.
Indicating that this base address
register describes an I/O base
address.
memory space requirement of 32
bytes.
3
PREFETCH Prefetchable. Read as zero; write
operations have no effect. Indi-
cates that memory space con-
trolled by this base address
register is not prefetchable. Data
in the memory mapped I/O space
cannot be prefetched. Because
one of the I/O resources in this
address space is a Reset regis-
ter, the order of the read access-
es is important.
PCI Memory Mapped I/O Base Address Register
Offset 14h
The PCI Memory Mapped I/O Base Address register is
a 32-bit register that determines the location of the
Am79C978 I/O resources in all of memory space. It is
located at offset 14h in the PCI Configuration Space.
Bit
Name
Description
2-1
TYPE
Memory type indicator. Read as
zeros; write operations have no
effect. Indicates that this base ad-
dress register is 32 bits wide and
mapping can be done anywhere
in the 32-bit memory space.
31-5
MEMBASE Memory mapped I/O base ad-
dress most significant 27 bits.
These bits are written by the host
to specify the location of the
Am79C978 I/O resources in all of
memory space. MEMBASE must
be written with a valid address
before the Am79C978 controller
slave memory mapped I/O mode
is turned on by setting the ME-
MEN bit (PCI Command register,
bit 1).
0
MEMSPACE Memory space indicator. Read
as zero; write operations have no
effect. Indicates that this base ad-
dress register describes a memo-
ry base address.
PCI Subsystem Vendor ID Register
When the Am79C978 controller
is enabled for memory mapped
I/O mode (MEMEN is set), it mon-
itors the PCI bus for a valid mem-
ory command. If the value on
AD[31:5] during the address
phase of the cycles matches the
Offset 2Ch
The PCI Subsystem Vendor ID register is a 16-bit reg-
ister that together with the PCI Subsystem ID uniquely
identifies the add-in card or subsystem the Am79C978
controller is used in. Subsystem Vendor IDs can be ob-
tained from the PCI SIG. A value of 0 (the default) indi-
cates that the Am79C978 controller does not support
subsystem identification. The PCI Subsystem Vendor
ID is an alias of BCR23, bits 15-0. It is programmable
through the EEPROM.
value
of
MEMBASE,
the
Am79C978 controller will drive
DEVSEL indicating it will respond
to the access.
MEMBASE is read and written by
the host. MEMBASE is cleared
by H_RESET and is not affected
by S_RESET or by setting the
STOP bit.
The PCI Subsystem Vendor ID register is located at off-
set 2Ch in the PCI Configuration Space. It is read only.
PCI Subsystem ID Register
Offset 2Eh
The PCI Subsystem ID register is a 16-bit register that
together with the PCI Subsystem Vendor ID uniquely
identifies the add-in card or subsystem the Am79C978
controller is used in. The value of the Subsystem ID is
up to the system vendor. A value of 0 (the default) indi-
cates that the Am79C978 controller does not support
subsystem identification. The PCI Subsystem ID is an
alias of BCR24, bits 15-0. It is programmable through
the EEPROM.
4
MEMSIZE
Memory mapped I/O size re-
quirements. Read as zeros; write
operations have no effect.
MEMSIZE indicates the size of
the
memory
space
the
Am79C978 controller requires.
When the host writes a value of
FFFF FFFFh to the Memory
Mapped I/O Base Address regis-
ter, it will read back a value of 0 in
bit 4. That indicates a Am79C978
The PCI Subsystem ID register is located at offset 2Eh
in the PCI Configuration Space. It is read only.
Am79C978
107
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