AM79C978 Datasheet, PDF (201/261 Pages) Advanced Micro Devices – Single-Chip 1/10 Mbps PCI Home Networking Controller

RMD0
Bit Name
31-0 RBADR
RMD1
Bit Name
31 OWN
30 ERR
29 FRAM
28 OFLO
27 CRC
Description
Receive Buffer address. This field
contains the address of the
receive buffer that is associated
with this descriptor.
Description
This bit indicates whether the de-
scriptor entry is owned by the
host (OWN = 0) or by the
Am79C978 controller (OWN = 1).
The Am79C978 controller clears
the OWN bit after filling the buffer
that the descriptor points to. The
host sets the OWN bit after emp-
tying the buffer.
Once the Am79C978 controller or
host has relinquished ownership
of a buffer, it must not change any
field in the descriptor entry.
ERR is the OR of FRAM, OFLO,
CRC, BUFF, or BPE. ERR is set
by the Am79C978 controller and
cleared by the host.
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
Am79C978 controller and
cleared by the host.
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 Am79C978
controller and cleared by the
host.
CRC indicates that the receiver
has detected a CRC (FCS) error
26 BUFF
25 STP
24 ENP
Am79C978
on the incoming frame. CRC is
valid only when ENP is set and
OFLO is not. CRC is set by the
Am79C978 controller and
cleared by the host. CRC will also
be set when Am79C978 home
networking receives an RX_ER
indication from the external PHY
through the MII.
Buffer error is set any time the
Am79C978 controller does not
own the next buffer while data
chaining a received frame. This
can occur in either of two ways:
1. The OWN bit of the next buffer
is 0.
2. FIFO overflow occurred before
the Am79C978 controller was
able to read the OWN bit of
the next descriptor.
If a Buffer Error occurs, an Over-
flow Error may also occur inter-
nally in the FIFO, but will not be
reported in the descriptor status
entry unless both BUFF and
OFLO errors occur at the same
time. BUFF is set by the
Am79C978 controller and
cleared by the host.
Start of Packet indicates that this
is the first buffer used by the
Am79C978 controller for this
frame. If STP and ENP are both
set to 1, the frame fits into a single
buffer. Otherwise, the frame is
spread over more than one buff-
er. When LAPPEN (CSR3, bit 5)
is cleared to 0, STP is set by the
Am79C978 controller and
cleared by the host. When LAP-
PEN is set to 1, STP must be set
by the host.
End of Packet indicates that this
is the last buffer used by the
Am79C978 controller for this
frame. It is used for data chaining
buffers. If both STP and ENP are
set, the frame fits into one buffer
and there is no data chaining.
ENP is set by the Am79C978
controller and cleared by the
host.
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