AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 233

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

8/01/00
Offset
Offset
0Ch
4
4
4
4
4
8
0
4
19-16
31-16
15-0
31-0
31:0
15-0
Bit
Bit
22
21
20
31
USER SPACE
RBADR[31:0]
TCI[15:0]
MCNT
Name
LAFM
BCNT
Name
OWN
BAM
PAM
Physical Address Match is set by the Am79C976 controller when it accepts the
received frame due to a match of the frame’s destination address with the content of
the physical address register. PAM is valid only when ENP is set. PAM is set by the
Am79C976 controller and cleared by the host.
This bit does not exist when the Am79C976 controller is programmed to use 16-bit
software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is
cleared to 0).
Logical Address Filter Match is set by the Am79C976 controller when it accepts the
received frame based on the value in the logical address filter register. LAFM is valid
only when ENP is set. LAFM is set by the Am79C976 controller and cleared by the
host.
Note that if DRCVBC (CSR15, bit 14) is cleared to 0, only BAM, but not LAFM will
be set when a Broadcast frame is received, even if the Logical Address Filter is
programmed in such a way that a Broadcast frame would pass the hash filter. If
DRCVBC is set to 1 and the Logical Address Filter is programmed in such a way that
a Broadcast frame would pass the hash filter, LAFM will be set on the reception of a
Broadcast frame.
This bit does not exist when the Am79C976 controller is programmed to use 16-bit
software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is
cleared to 0).
Broadcast Address Match is set by the Am79C976 controller when it accepts the
received frame, because the frame’s destination address is of the type ’Broadcast.’
BAM is valid only when ENP is set. BAM is set by the Am79C976 controller and
cleared by the host.
This bit does not exist when the Am79C976 controller is programmed to use 16-bit
software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is
cleared to 0).
Reserved.
Buffer Byte Count is the length of the buffer pointed to by this descriptor, expressed
as the two’s complement of the length of the buffer. This field is written by the host
and unchanged by the Am79C976 controller.
Receive Buffer Address. This field contains the address of the receive buffer that is
associated with this descriptor.
User Space. Reserved for user defined data.
VLAN Tag Control Information copied from the received frame.
Message Byte Count is the number of bytes of the received message written to the
receive buffer. This is the actual frame length (including FCS) unless stripping is
enabled and the length field is < 46 bytes. In this case, MCNT is 14 + length_field.
MCNT can take values in the range 15 to 59 and values greater than or equal to 64.
MCNT is expressed as an unsigned binary integer. MCNT is valid only when ERR is
clear and ENP is set. MCNT is written by the Am79C976 controller and cleared by
the host.
This bit indicates whether the descriptor entry is owned by the host (OWN = 0) or by
the Am79C976 controller (OWN = 1). The host sets the OWN bit after it has emptied
the buffer pointed to by the descriptor entry. The Am79C976 controller clears the
OWN bit after filling the buffer that the descriptor points to. Both the Am79C976
controller and the host must not alter a descriptor entry after it has relinquished
ownership.
P R E L I M I N A R Y
Am79C976
Description
Description
233