Am79C971
171
P R E L I M I N A R Y
The value of the SSIZE32 bit has
no effect on the drive of the upper
8 address bits. The upper 8 ad-
dress pins are always driven, re-
gardless of the state of the
SSIZE32 bit.
Note that the setting of the
SSIZE32 bit has no effect on the
defined width for I/O resources.
I/O resource width is determined
by the state of the DWIO bit
(BCR18, bit 7).
7-0
SWSTYLE
Software Style register. The val-
ue in this register determines the
style of register and memory re-
sources that shall be used by the
Am79C971 controller. The Soft-
ware Style selection will affect the
interpretation of a few bits within
the CSR space, the order of the
descriptor entries and the width of
the descriptors and initialization
block entries.
All Am79C971 controller CSR
bits and all descriptor, buffer, and
initialization block entries not cit-
ed in the Table 36 are unaffected
by the Software Style selection
and are, therefore, always fully
functional as specified in the CSR
and BCR sections.
Read/Write accessible only when
either the STOP or the SPND bit
is set. The SWSTYLE register will
contain the value 00h following
H_RESET and will be unaffected
by S_RESET or STOP.
BCR21: Interrupt Control
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
15-0
INTCON
Reserved locations. Writes to this
register will have no effect on the
operation of the Am79C971 con-
troller.
BCR22: PCI Latency Register
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
Am79C971 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 Am79C971 Latency
Timer register.
Read accessible always; write
accessible only when either the
STOP or the SPND bit is set.
MAX_LAT is set to the value of
FFh by H_RESET which results
in a default maximum latency of
63.75 microseconds. It is recom-
Table 36.
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
Undefined
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 access only
All Other
Reserved
Undefined
Undefined