AM79C971VCW datasheet(184/265 Pages) AMD

184 / 265 page

184

Am79C971

P R E L I M INARY

Once the Am79C971 controller or

host has relinquished ownership

of a buffer, it must not change any

field in the descriptor entry.

ERR

ERR is the OR of FRAM, OFLO,

CRC, BUFF, or BPE. ERR is set

by the Am79C971 controller and

cleared by the host.

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

Am79C971

controller

and

cleared by the host.

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 Am79C971

controller and cleared by the

host.

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

Am79C971

controller

and

cleared by the host. CRC will also

be set when Am79C971 receives

an RX_ER indication from the ex-

ternal PHY through the MII.

BUFF

Buffer error is set any time the

Am79C971 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 Am79C971 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

set

the

Am79C971

controller

and

cleared by the host.

STP

Start of Packet indicates that this

is the first buffer used by the

Am79C971

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

Am79C971

controller

and

cleared by the host. When LAP-

PEN is set to 1, STP must be set

by the host.

ENP

End of Packet indicates that this

is the last buffer used by the

Am79C971

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 Am79C971

controller and cleared by the

host.

BPE

Bus Parity Error is set by the

Am79C971 controller when a par-

ity error occurred on the bus inter-

face during data transfers to a

receive buffer. BPE is valid only

when ENP, OFLO, or BUFF are

set. The Am79C971 controller will

only set BPE when the advanced

parity error handling is enabled

by setting APERREN (BCR20, bit

10) to 1. BPE is set by the

Am79C971

controller

and

cleared by the host.

This bit does not exist when the

Am79C971

controller

pro-

grammed to use 16-bit software

structures for the descriptor ring

entries (BCR20, bits 7-0, SW-

STYLE is cleared to 0).

PAM

Physical Address Match is set by

the Am79C971 controller when it

accepts the received frame due

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