DP83261 datasheet(96/132 Pages) NSC

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70 Signal Descriptions (Continued)

State Descriptions

MR0 Not Ready

In this state the Ring Engine does not have a Service Op-

portunity If RQRCLS is not zero the Ring Engine is trying to

secure a Service Opportunity meeting the requested service

parameters

On a valid Service Opportunity the MR(01) transition is tak-

en The status signals TXED and TXABORT are cleared and

TXRDY is set to indicate that the Transmitter is ready to

service a request

MR1 Ready

In this state the Ring Engine has secured a Service Oppor-

tunity and is ready to service the current request The Trans-

mitter is sourcing Preamble Fill or internally generated Void

(from the Data state) Claim (from the Claim state) or Bea-

con (from the Beacon state) frames

The Service Opportunity is governed by the requested serv-

ice parameters If an unserviceable request is presented for

one or more cycles the Service Opportunity ends If THT

expires or a priority threshold is reached the Service Oppor-

tunity will end immediately or after the next frame depend-

ing on the state of the send window

The send window is an opportunity to send a frame without

being interrupted by time thresholds The Service Opportu-

nity may end during a send window if the service parame-

ters change

The send window opens each time TXRDY is asserted (en-

try to MR1) It remains open for a minimum of 6 byte times

The send window also opens if RQRDY is asserted while

TXRDY is asserted and if TXPASS is not asserted within

one byte time after RQRDY is asserted

The send window is held open until

1) RQSEND or RQFINAL is asserted or

2) until L

Max has expired (320 ms) a Void frame has

been sent (096 ms or 160 ms) and 7 more bytes of

preamble have been sent (056 ms)

(When Op-

tionIRPT e 1 this condition does not apply)

At any time after RQRDY has been asserted and the final

frame of the request has been sent RQFINAL may be as-

serted to indicate that a token of the Issue Token Class

should be transmitted at the end of the current Service Op-

portunity If the MR(10) transition occurs while RQFINAL is

asserted and all the other conditions for accepting RQFI-

NAL hold the transmitted token will be of the Issue Token

Class

After RQFINAL has been asserted no more frames can be

sent until RQRDY has been deasserted and then reassert-

ed RQRDY should be deasserted and the service parame-

ters updated to reflect the next request (if any) as soon as

possible to allow the Ring Engine to make better ring

scheduling decisions If RQRDY is not deasserted by the

end of the last frame of a Service Opportunity a Void frame

will be transmitted before the token

When the Service Opportunity ends the MR(10) transition is

taken and TXPASS is asserted to indicate the end of the

current Service Opportunity RQFINAL (and RQRDY) must

be asserted not later than one byte time after TXPASS to

insure that a token of the appropriate issue class is issued

When a frame can be sent from the interface the MR(12)

transition is taken and TXACK is set to indicate that the

Transmitter is sending the frame

The state diagram for the internal substates within state

MR1 is shown in

Figure 7-12

TLF10387 – 19

FIGURE 7-12 MR1 Substate Diagram

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