IBM 5280 Distributed Data System - Index of

User Defined Error RecoveryWhen a program instruction loads a data set into another partition, or if the loadtakes place through a common function, the load instruction can indicate that userdefined error recovery procedures will handle error recovery. If the load operationis successful, control returns to the second instruction following the load instruction.If an error occurs during the load operation, the main microprocessor placesthe error code into a system binary register (BR16) and returns control to the firstinstruction following the load instruction. This instruction usually branches to theerror recovery procedures.Main Microprocessor Error RecoveryThere are four types of error recovery procedures, depending on the type of loadtaking place when the error occurred. When any type of error occurs, the mainmicroprocessor sends an error message to the screen and waits for the operator topress the Reset key. After the reset, error recovery is as follows for the differenttypes of loads:Global load, prompts for the load parameters to be entered from the keyboard.After reset, the load prompt is redisplayed with the original information that wasentered. The operator can then enter the correct information.Program instruction reloading the same partition, with the standard load promptin the common functions area available. After reset, the load instruction ~ replacedwith the standard load prompt, which prompts for the load parameters to be loadedfrom the keyboard.Program instruction reloading the same partition, with no standard load promptavailable. There is no way to retry this type of load. The main microprocessorissues an exit instruction and goes to the next partition. The partition that wasbeing loaded is available to be loaded by another partition.Program instruction loading another partition. After reset, the load instruction isnot retried. The partition that was being loaded is made available to be loaded byanother load instruction or by the standard load processor. Control returns to theinstruction following the load instruction.SUBROUTINESThe 5280 supports a variable-length address stack for use during subroutine callsand returns. The assembler places the address (relative to the start of the partition)of the address stack into B R 18. During program execution when a subroutine callis executed, the main microprocessor places the 2-byte absolute address of the nextsequential instruction into the address stack pointed to by BR18. Then the contentof B R 18 is incremented by 2 so that it points to the next available 2-byte entry inthe address stack. When a return is executed, the content of BR18 is decrementedby 2, and the address stored in the address stack at the location pointed to by BR18is taken as the return address.5280 Functions and Storage Overview 15