AMD
P R E L I M I N A R Y
158
Am79C970A
PCnet-PCI II controller utilizes
32-bit software structures for the
initialization block and the trans-
mit and receive descriptor en-
tries. When cleared, this bit
indicates that the PCnet-PCI II
controller utilizes 16-bit software
structures for the initialization
block and the transmit and
receive descriptor entries. In this
mode the PCnet-PCI II controller
is backwards compatible with
the Am79C90 C-LANCE and
Am79C960 PCnet-ISA.
The value of SSIZE32 is deter-
mined by the PCnet-PCI II con-
troller according to the setting of
the Software Style (SWSTYLE,
bits 7–0 of this register).
Read
SSIZE32 is read only. Write op-
erations
will
SSIZE32 will be cleared after
H_RESET (since SWSTYLE de-
faults to ZERO) and is not af-
fected by S_RESET or by setting
the STOP bit.
accessible
always.
be
ignored.
If SSIZE32 is cleared to ZERO,
then bits IADR[31:24] of CSR2
will be used to generate values
for the upper 8 bits of the 32 bit
address bus during master
accesses
initiated
PCnet-PCI II controller. This ac-
tion is required, since the 16-bit
software structures will yield
only 24 bits of address for
PCnet-PCI II controller bus
master accesses.
by
the
If SSIZE32 is set to ONE, then
the software structures that are
common to the PCnet-PCI II
controller and the host system
will supply a full 32 bits for each
address pointer that is needed by
the PCnet-PCI II controller for
performing master accesses.
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
width for I/O accesses. I/O
access width is determined by
the state of the DWIO bit
(BCR18, bit 7).
7–0 SWSTYLE
Software Style register. The
value in this register determines
the style of register and memory
resources that shall be used by
the PCnet-PCI II controller. The
Software Style selection will
affect the interpretation of a few
bits within the CSR space, the or-
der of the descriptor entries and
the width of the descriptors and
initialization block entries.
All PCnet-PCI II controller CSR
bits and BCR bits and all
descriptor, buffer and initializa-
tion block entries not cited in the
table above are unaffected by the
software style selection.
Table 35. Software Styles
SWSTYLE
[7:0]
Initialization
Block Entries
Descriptor
Ring Entries
Altered Bit
Interpretations
Style Name CSRPCNET
SSIZE32
00h
C-LANCE
/
PCnet-ISA
1
0
16-bit software
structures, non-burst
or burst access
16-bit software
structures, non-burst
access only
All bits in CSR4 are
used, TMD1[29] is
ADD_FCS
01h
ILACC
0
1
32-bit software
structures, non-burst
or burst access
32-bit software
structures, non-burst
access only
CSR4[9:8],CSR4[5:4]
and CSR4[1:0] have
no function, TMD1[29]
is NO_FCS.
02h
PCnet-PCI
1
1
32-bit software
structures, non-burst
or burst access
32-bit software
structures, non-burst
access only
All bits in CSR4 are
used, TMD1[29] is
ADD_FCS
03h
PCnet-PCI II
Controller
1
1
32-bit software
structures, non-burst
or burst access
32-bit software
structures, non-burst
or burst access
All bits in CSR4 are
used, TMD1[29] is
ADD_FCS
All Other
Undefined
Undefined
Undefined
Undefined
Undefined
Undefined