FRR Stack Header

Table 1 shows useful fields in the FRR stack header.

Table 1. Useful fields in an FRR Stack Header
Field Name	Offset into FRR Stack	Description
FRRSEMP	+X'0'	Address indicating an empty stack
FRRSLAST	+X'04'	Address of the last entry in the stack
FRRSELEN	+X'08'	Length of each FRR entry in the stack. This field contains a constant value of X'00000020'
FRRSCURR	+X'0C'	Address of current FRR entry. If this entry is equal to FRRSEMP at offset X'0' then the FRR stack is empty.
FRRSRTMW	+X'28'	Indicates whether RTM1 is active on the processor associated with this FRR. A non-zero value indicates that this FRR stack contains valid, current data. The error type is found at offset +2 into this field: X'01' - program check X'02' - restart key X'03' - SVC error. An SVC was issued while in locked, disabled, or SRB mode X'04' - DAT error X'05' - machine check X'06' - STERM reentry
FRRSRTMA	+X'38'	Pointer to the RT1WA control block. Useful fields in the RT1WA control block include: RT1WRTCA (RT1WA +X'2C') - Pointer to the SDWA control block currently in use. RT1WEED (RT1WA +X'30') - Pointer to the EED control blocks acquired. RT1WMODE (RT1WA +X'34') - Contains the mode at the time of entry to RTM1. The mode is one of the following: X'80' - supervisor control mode (PSASUPER≠0) X'40' - physically disabled mode X'20' - global spin lock held X'10' - global suspend lock held X'08' - local lock held X'04' - Type 1 SVC mode X'02' - SRB mode X'01' - unlocked task mode RT1WSRMD (RT1WA +X'35') - Contains the current system mode.
FRRSENTS	+X'58'	Beginning for FRR stack entries.