DP83266 datasheet(27/152 Pages) NSC

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50 Functional Description

(Ring Engine) (Continued)

On the PHY Request interface parity is generated for inter-

nally sourced fields (such as the SA or FCS on frames when

not using SA or FCS transparency and internally generated

Beacon Claim and Void frames) Odd parity is always gen-

erated for PRP This allows through parity support at the

PHY interface even if parity is not used at the MAC inter-

face This is very desirable since every byte of data that

traverses the ring travels across the PHY Interface which is

actually part of the ring

Through parity is not supported in the Control Interface Reg-

isters and the Parameter RAM Parity is generated and

stripped at the Control Interface

Handling Parity Errors

Parity errors are reported in the Exception Status Register

when parity on that interface is enabled

A parity error at the PHY interface (when ModePIP is set) is

treated as a code violation and ESRPPE is set If the parity

error occurs in the middle of token or frame reception the

token or frame is stripped a Format Error is signalled

(FOERROR) and the Lost Count is incremented

A parity error at the MAC Interface (when ModeMRP is set)

during a frame transmission from the MAC interface (while

TXACK is asserted) causes the frame transmission to be

aborted When a frame is aborted a Void frame is transmit-

ted to reset every station’s TVX timer A parity error (when

enabled) causes ESRMPE to be set

A parity error at the Control Interface (when ModeCBP is

set) will cancel the current write access ESRCPE is set to

indicate that a parity error occurred and ESRCCE is set to

indicate that the write was not performed

512 HANDLING INTERNAL ERRORS

Errors internal to the Ring Engine cause a MAC Reset This

includes detecting illegal states in the state machines Inter-

nal Errors are reported in the Internal Error Latch Register

(IELR) After an internal state machine error is detected and

reported

(IELRRSMERR

for

the

receiver

and

IELRTSMERR for the transmitter) the current state regis-

ters continue to be updated as always

In diagnose mode the Current Receive and Transmit Status

Registers are frozen with the errored state until the internal

state machine error condition is cleared (IELRRSMERR

andor IELRTSMERR)

60 Functional Description

(Service Engine)

61 OVERVIEW

The Service Engine consists of two major blocks the Indi-

cate Machine and the Request Machine These blocks

share the Bus Interface Unit StatusSpace Machine Point-

er RAM and Limit RAM blocks

The Service Engine provides an interface between the Ring

Engine FDDI Media Access Control Protocol block and a

host system The Service Engine transfers FDDI frames be-

tween the FDDI device and host memory

611 Indicate Machine

On the Receive side (from the ring) the Indicate Machine

sequences through the incoming byte stream from the Ring

Engine Received frames are sorted onto Indicate Channels

and a decision is made whether or not to copy them to host

memory The Indicate Machine uses the control signals pro-

vided by the Ring Engine Receive State Machine on the

MAC Indicate Interface to make this decision

612 Request Machine

On the Transmit side (to the ring) the Request Machine pre-

pares one or more frames from host memory for transmis-

sion to the Ring Engine The Request Machine provides all

the control signals to drive the Ring Engine Request Inter-

face

62 OPERATION

621 Indicate Operation

The Indicate Block accepts data from the Ring Engine as a

byte stream

Upon receiving the data the Indicate Block performs the

following functions

Decodes the Frame Control field to determine the frame

type

Sorts the received frames onto Channels according to

the Sort Mode

Optionally Filters identical MAC frames

Filters Void frames

Copies the received frames to memory according to

Copy Criteria

Writes status for the received frames to the Indicate

Status Queue

Issues interrupts to the host on host-defined status

breakpoints

The Indicate Machine decodes the Frame Control (FC) field

to determine the type of frame The following types of

frames are recognized Logical Link Control (LLC) Restrict-

ed Token Unrestricted Token Reserved Station Manage-

ment (SMT) SMT Next Station Addressing MAC Beacon

MAC Claim Other MAC and Implementer

The Indicate Machine sorts incoming frames onto Indicate

Channels according to the frame’s FC field the state of the

AFLAG signal from the Ring Engine (which indicates that

the MACSI device had an internal address match) and the

host-defined sorting mode programmed in the Sort Mode

field of the Indicate Mode Register SMT and MAC frames

are always sorted onto Indicate Channel 0 On Indicate

Channels 1 and 2 frames can be sorted according to

whether they are synchronous or asynchronous or whether

they are high-priority asynchronous or low-priority asynchro-

nous Frames can also be sorted by whether their address

matches an internal (MACSI device) or external address or

based on header and Information fields for all non-MAC

SMT frames

The SynchronousAsynchronous Sort Mode is intended for

use in end-stations or applications using synchronous trans-

mission

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