
206
Am79C973/Am79C975
P R E L I M I N A R Y
RMD0
Bit
Name
Description
31-0
RBADR
Receive Buffer address. This field
contains the address of the re-
ceive buffer that is associated
with this descriptor.
RMD1
Bit
Name
Description
31
OWN
This bit indicates whether the de-
scriptor entry is owned by the
host (OWN = 0) or by the
Am79C973/Am79C975 controller
(OWN = 1). The Am79C973/
Am79C975 controller clears the
OWN bit after filling the buffer that
the descriptor points to. The host
sets the OWN bit after emptying
the buffer.
Once the Am79C973/Am79C975
controller or host has relin-
quished ownership of a buffer, it
must not change any field in the
descriptor entry.
30
ERR
ERR is the OR of FRAM, OFLO,
CRC, BUFF, or BPE. ERR is set
by the Am79C973/Am79C975
controller and cleared by the
host.
29
FRAM
Framing error indicates that the
incoming frame contains a non-
integer multiple of eight bits and
there was an FCS error. If there
was no FCS error on the incom-
ing frame, then FRAM will not be
set even if there was a non-
integer multiple of eight bits in the
frame. FRAM is not valid in inter-
nal loopback mode. FRAM is val-
id only when ENP is set and
OFLO is not. FRAM is set by the
Am79C973/Am79C975 controller
and cleared by the host.
28
OFLO
Overflow error indicates that the
receiver has lost all or part of the
incoming frame, due to an inabili-
ty to move data from the receive
FIFO into a memory buffer before
the internal FIFO overflowed.
OFLO is set by the Am79C973/
Am79C975
controller
cleared by the host.
and
27
CRC
CRC indicates that the receiver
has detected a CRC (FCS) error
on the incoming frame. CRC is
valid only when ENP is set and
OFLO is not. CRC is set by the
Am79C973/Am79C975 controller
and cleared by the host. CRC will
also be set when Am79C973/
Am79C975 receives an RX_ER
indication from the external PHY
through the MII.
26
BUFF
Buffer error is set any time the
Am79C973/Am79C975 controller
does not own the next buffer
Table 59. Receive Descriptor (SWSTYLE = 2)
28
27
26
25
RBADR[31:0]
OFL
O
F
RFRTAG[14:0]
USER SPACE
Address
CRDA+00h
31
30
29
24
23
22
21
20
19-16
15-12
11-0
CRDA+04h OWN ERR
FRA
M
CRC
BUF
STP
ENP
BPE
PAM
LAFM
BAM
RES
1111
BCNT
CRDA+08h
CRDA+0Ch
RES
0000
MCNT
Table 60. Receive Descriptor (SWSTYLE = 3)
29
28
27
26
RES
FRAM
OFLO
CRC
BUFF
Address
CRDA+00h
CRDA+04h
CRDA+08h
CRDA+0Ch
31
30
25
24
23
RES
BPE
22-16
RES
RES
15-12
0000
1111
11-0
MCNT
BCNT
OWN
ERR
STP
ENP
RBADR[31:0]
USER SPACE