Note the execution of an unlock control command

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Unformatted text preview: aced a ‘valid’ Transfer Frame (a Transfer Frame that has passed the Frame Validation Check defined in reference [3]) into a buffer of FARM-1. However, the following operation needs to be performed by FARM-1 before the FARM-1 State Table is applied: verifying that a Type-BC Transfer Frame contains one of the two COP-1 control commands (‘Unlock’ and ‘Set V(R)’). Included in the FARM-1 State Table are the following operations: a) checking the value of the ‘Bypass’ Flag; b) checking the value of the ‘Control Command’ Flag; c) checking the value of N(S) in Type-AD Transfer Frames. 6.3.2.2 Control Commands In table 6-1, Events E7 and E8 are concerned with the execution of, respectively, an ‘Unlock’ Control Command and a ‘Set V(R)’ Control Command. The specification of each action in each box is self-explanatory. The action described for Event E8 in State (S3) means that the ‘Set V(R)’ Control Command is not executed (FARM-1 must be ‘unlocked’ first), but its receipt is accounted for by means of the FARM-B_Counter since the control command was validated as ‘legal’ and found ‘executable’. NOTE – The execution of an ‘Unlock’ Control Command resets only FARM-1, not the Higher Procedures. Some mechanism should be provided to ensure that the data management functions of the Higher Procedures purge/reset their buffers as required for operations of the protocol. 6.3.2.3 Buffer Release Signal If an implementation provides a scheme for flow control between FARM-1 and the Higher Procedures and the flow control scheme ever results in the COP-1 Wait_Flag being set, the scheme must also provide a ‘Buffer Release Signal’, which corresponds to Event E10 in the FARM-1 State Table. In this case, FARM-1 shall be signaled when sufficient buffer space becomes available for at least one more maximum-size Frame. 6.3.2.4 CLCW FARM-1 constantly provides some information to be sent back to FOP-1 in the CLCW (Event E11 in the FARM-1 State Table). CCSDS 232.1-B-2 Page 6-8 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 6.3.3 FARM-1 STATE TRANSITIONS A summary of the way FARM-1 moves between states is depicted in figure 6-2. Table 6-1: FARM-1 State Table (Part 1) State Name WAIT LOCKOUT Main Feature of State Normal state accept frames Wait_Flag to is on Lockout_ Flag is on State Number Event Conditions OPEN S1 S2 S3 Event Number N(S) = V(R) A buffer is available for this frame E1 Accept frame, Not applica...
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