Functional Description
The processor should read RBCH, RBCL after each RPF, RME interrupt. If after an
RPF or RME the byte count exceeds 528 then CMDR:RRES should be written (abort
of frame). The frame was invalid in this case but it was not a frame rejection condition.
If after a RME the byte count was between 260 and 528 inclusively and no other
invalidity condition according to section 1 applies or a data overflow according to
section 2 occurred then a frame rejection condition is detected.
Necessary Software Reactions
The software can find out all frame rejection conditions either by receiving PCE or by checking
RSTA, SAPR, RHCR, RBCH, RBCL after a RME interrupt, and RBCH, RBCL after an RPF
interrupt. In case of U-frames it has to be checked before, whether or not it is an invalid frame
and has only to be discarded or, whether it was valid but leads to a frame rejection condition.
(Only valid frames can lead to frame rejection conditions according to § 5.8.4 of Q.921).
In case of a frame rejection condition the software has to take the actions defined in § 5.7.2
and issue a MDL-ERROR-INDICATION.
The particular action in § 5.7.2 reads:
§ 5.7.2 Procedures
In all re-establishment situations, the data link layer entity shall follow the procedures defined
in § 5.5.1. All locally generated conditions for re-establishment will cause the transmission of
the SABME.
In case of data link layer and peer initiated re-establishments, the data link layer entity shall
also
– Issue a MDL-ERROR-INDICATION primitive to the connection management entity: and
– rf V(S) > V(A) prior to re-establishment issue a DL-ESTABLISH-INDICATION primitive
to layer 3 and discard all l queues.
In case of layer-3 initiated re-establishment, or if a DL-ESTABLISH-REQUEST primitive
occurs pending re-establishment, the DL-ESTABLISH-CONFIRM primitive shall be used.
A frame rejection condition is not a peer initiated re-establishment.
§ 5.5.1 is pretty voluminous. Here just the necessary actions to be done with the ISAC-S shall
be given, in case the re-establishment is successful at once:
– the software should set the ISAC-S into non-auto mode by writing the Mode register
MODE: 6x . Further actions that result from switching to non-auto mode should also be
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taken according.
– it should write FIFO : 76 , 6F , CMDR : XTF to send a SABME-command with p = 1.
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– upon having received a correct UA-frame it should
– write CMDR : XRES, RRES to set V(S) = V(A) = V(R) = 0
– write MODE: 3x to re-enter auto mode for the multiple-frame established state.
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If the re-establishment is not successful at once, in the non-auto-mode further software actions
according to § 5.5.1 have to be taken.
Semiconductor Group
128
INFINEON [ Infineon ]
