AM79C975VCW datasheet(206/304 Pages) AMD

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206

Am79C973/Am79C975

P R E L I M INARY

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

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

host

has

relin-

quished 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

the

Am79C973/Am79C975

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

Am79C973/Am79C975 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 Am79C973/

Am79C975

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

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.

BUFF

Buffer error is set any time the

Am79C973/Am79C975 controller

does not own the next buffer

Table 59. Receive Descriptor (SWSTYLE = 2)

Address

19-16

15-12

11-0

CRDA+00h

RBADR[31:0]

CRDA+04h OWN ERR

FRA

OFL

CRC

BUF

STP

ENP

BPE

PAM

LAFM

BAM

RES

1111

BCNT

CRDA+08h RES

RFRTAG[14:0]

0000

MCNT

CRDA+0Ch

USER SPACE

Table 60. Receive Descriptor (SWSTYLE = 3)

Address

22-16

15-12

11-0

CRDA+00h

RES

0000

MCNT

CRDA+04h

OWN

ERR

FRAM

OFLO

CRC

BUFF

STP

ENP

BPE

RES

1111

BCNT

CRDA+08h

RBADR[31:0]

CRDA+0Ch

USER SPACE

AM79C975VCW Datasheet(PDF) 206 Page - Advanced Micro Devices

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