DIE characteristics
The entry environment is:
| Environmental factor | Requirement |
|---|---|
| Authorization: | Supervisor state and PSW key 0. |
| Dispatchable unit mode: | Task or SRB |
| Cross memory mode: | Any PASN, any HASN, any SASN |
| AMODE: | 24-bit or 31-bit depending on TQEXMODE bit when the DIE was set. |
| ASC mode: | Primary |
| Interrupt status: | Disabled for I/O and external interrupts |
| Locks: | The local, CMS, and/or CPU locks may be held. |
| Control parameters: | No requirement. |
Register contents upon entry are as follows:
- The contents of register 0 is unpredictable.
- Register 1 contains the address of the TQE. At this time the TQE is not enqueued upon the real time queue. Fields TQETCB and TQEASCB respectively contain a TCB address and an ASCB address, if previously set by the user on entry to the set DIE service routine.
- The low-order words of registers 2 - 12 are as they were upon entry to the set DIE service routine (or as changed by a previous DIE entry -- see DIE execution).
- The contents of register 13 is unpredictable.
- Register 14 contains the return address.
- Register 15 contains the entry point of the DIE routine.
- The contents of floating point registers are unpredictable.
The contents of vector registers
(VRs) are unpredictable. The DIE must not use VRs.
- Access registers and the high halves of general purpose registers are unpredictable on entry to a DIE routine.
While a system program has a TQE enqueued upon the real time queue, it must ensure that the associated DIE routine is available for the timer SLIH (second level interrupt handler) to access from any address space. Additionally, because the DIE is entered disabled, its code must be resident or fixed to avoid a page fault at entry.