gtpn1m0s | Non-SNA Data Communications Reference |
Input CCP adds all LCBs except for ENQ to the input LCB queue and activates link controller if it is not already active. ENQ LCBs and message blocks are added either to the input list or post interrupt (Ready) list dependent upon a system parameter. The branch vector is set to direct them to link OPZO, which adds them to the channel input block queue. Input message handler directs ENQs to link controller and assembles a complete message which is then passed to the SLC component of the communications source program. Link controller is entered to send ACK or NAK according to the state of the block received by input message handler. Blocks are checked for an ETB and if none is found a system error is generated. Link or channel conditions which prevent acceptance of message blocks are tested and, if necessary, the blocks are discarded. Blocks are then checked for parity or TSI sequence errors and the link controller is entered to generate and transmit a NAK LCB if either has occurred. Blocks of multi-block messages are filled with the file address of the previous block placed in it, that is, they are chained together in reverse order to that in which they were received. When the last block is received (that is, the message is complete), the constituent blocks are retrieved from file and reassembled in the correct order according to the MBI prior to entering communications source.
SLC communications source translates the message text from line transmission code to EBCDIC according to the translate code that is indicated in the ACI or in the link keypoint and then reformats the text for type A or type B messages. Type B messages are placed in XM0RL format and passed to XIMA. Type A messages are placed in AM0SG format, and a routing control parameter list (RC0PL) is constructed and placed in the ECB. Type A traffic containing a pseudo line number is passed to the common component of the Communications Source Program. Type A traffic not containing a pseudo line number is passed to the message router, if it exists in the system, or a user defined application program.