AM79C978A Datasheet, PDF (200/256 Pages) Advanced Micro Devices – Single-Chip 1/10 Mbps PCI Home Networking Controller

15-12 ZEROS
11-0 MCNT
RXFRTG (CSR7, bit 14) is set to
0, RFRTAG will be read as all ze-
ros. See the section on Receive
Frame Tagging for details.
This field is reserved. The
Am79C978A controller will write
zeros to these locations.
Message Byte Count is the length
in bytes of the received message,
expressed as an unsigned binary
integer. MCNT is valid only when
ERR is clear and ENP is set.
MCNT is written by the
Am79C978A controller and
cleared by the host.
RMD3
Bit Name
Description
31-0 US
User Space. Reserved for user
defined space.
Transmit Descriptors
When SWSTYLE (BCR20, bits 7-0) is set to 0, the soft-
ware structures are defined to be 16 bits wide, and
transmit descriptors look like Table 83 (CXDA = Current
Transmit Descriptor Address).
When SWSTYLE (BCR 20, bits 7-0) is set to 2, the
software structures are defined to be 32 bits wide, and
transmit descriptors look like Table 84 (CXDA = Current
Transmit Descriptor Address).
When SWSTYLE (BCR 20, bits 7-0) is set to 3, then the
software structures are defined to be 32 bits wide, and
transmit descriptors look like Table 85 (CXDA = Current
Transmit Descriptor Address).
Address
CXDA+00h
CXDA+02h
CXDA+04h
CXDA+06h
15
OWN
1
BUFF
Table 83. Transmit Descriptor (SWSTYLE = 0)
14
ERR
1
UFLO
13
12
ADD_
FCS
1
EXDEF
MORE/
LTINT
1
LCOL
11
10
TBADR[15:0]
ONE
DEF
LCAR RTRY
9
8
7-0
STP
ENP
TBADR[23:16]
BCNT
TDR
Table 84. Transmit Descriptor (SWSTYLE = 2)
Address
CXDA+00h
CXDA+04h
CXDA+08h
CXDA+0Ch
31
OWN
BUFF
30
29
28
27
ERR
ADD_
FCS
MORE/
LTINT
ONE
UFLO EXDEF LCOL LCAR
26
25 24
TBADR[31:0]
DEF STP ENP
RTRY RES RES
USER SPACE
23
BPE
RES
22-16
RES
RES
15-12
1111
RES
11-4 3-0
BCNT
RES TRC
Table 85. Transmit Descriptor (SWSTYLE = 3)
Address 31
CXDA+00h BUFF
CXDA+04h OWN
CXDA+08h
CXDA+0Ch
30
UFLO
ERR
29
EXDEF
ADD_
FCS
28
LCOL
MORE/
LTINT
27
LCAR
ONE
26
25 24
RTRY
DEF STP ENP
TBADR[31:0]
USER SPACE
23 22-16
RES
BPE RES
15-12
1111
11-4
RES
3-0
TRC
BCNT
200
Am79C978A