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214
Am79C976
8/01/00
P R E L I M I N A R Y
0<($
Note:
Bits 15-0 in this register are programmable
through the EEPROM.
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-8
MAX_LAT
Maximum Latency. Specifies the
maximum arbitration latency the
Am79C976 controller can sustain
without causing problems to the
network activity. The register val-
ue specifies the time in units of
1/4 microseconds. MAX_LAT is
aliased to the PCI configuration
space register MAX_LAT (offset
3Fh). The host will use the value
in the register to determine the
setting of the Am79C976 Latency
Timer register.
Read/Write
MAX_LAT is set to the value of
18h by H_RESET which results
in a default maximum latency of 6
microseconds. MAX_LAT is not
affected by S_RESET or STOP.
accessible.
7-0
MIN_GNT
Minimum Grant. Specifies the min-
imum length of a burst period the
Am79C976 controller needs to
keep up with the network activity.
The length of the burst period is
calculated assuming a clock rate of
33 MHz. The register value speci-
fies the time in units of 1/4 μs.
MIN_GNT is aliased to the PCI
configuration
space
MIN_GNT (offset 3Eh). The host
will use the value in the register to
determine the setting of the
Am79C976
Latency
register.
register
Timer
Read/Write
MIN_GNT is set to the value of
18h by H_RESET which results
in a default minimum grant of 6
μs. MIN_GNT is not affected by
S_RESET or STOP.
accessible.
05$!=*
Note:
Bits 15-0 in this register are programmable
through the EEPROM.
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-0
SVID
Subsystem Vendor ID. SVID is
used together with SID (BCR24,
bits 15-0) to uniquely identify the
add-in board or subsystem the
Am79C976 controller is used in.
Subsystem Vendor IDs can be ob-
tained from the PCI SIG. A value
of 0 (the default) indicates that the
Am79C976 controller does not
support subsystem identification.
Table 92. Software Styles
SWSTYLE
[7:0]
Style
Name
LANCE/
PCnet-ISA
controller
RES
SSIZE32
Initialization Block
Entries
16-bit software
structures, non-burst or
burst access
RES
32-bit software
structures, non-burst or
burst access
32-bit software
structures, non-burst or
burst access
Descriptor Ring Entries
00h
0
16-bit software structures,
non-burst access only
01h
1
RES
02h
PCnet-PCI
controller
1
32-bit software structures,
non-burst access only
03h
PCnet-PCI
controller
1
32-bit software structures,
non-burst or burst access
04h
VLAN
1
Not used
32-bit software structures,
non-burst or burst access
32-bit software structures,
32-byte descriptors, non-
burst or burst access
Undefined
05h
64-bit address
1
Not used
All Other
Reserved
Undefined
Undefined