Generating an SVC

This form of MODESET, which executes as APF-authorized, in supervisor state, or under PSW key 0-7, changes the status of programs between supervisor state and problem program state, and key zero and non-key zero. The parameters that must be specified to perform the changes are MODE and KEY respectively.

The MODE parameter specifies whether bit 15 of the PSW is to be set to one or zero. When PSW bit 15 is one, the processor is in the problem state. For problem state, the caller’s PSW Key Mask (PKM) is set according to the following rules:

The bit matching the resulting PSW key is set on.
The bit matching key 9 is set on.
For a task attached with ATTACHX using the KEY=NINE parameter, the bits that were on in the PKM of the ATTACHX issuer are set on.
All other bits are set off.

When PSW bit 15 is zero, the processor is in supervisor state and the PSW Key Mask is unchanged.

The KEY parameter specifies whether bits 8-11 are to be set to zero or set to the value in the caller's TCB. Bits 8-11 form the processor protection key. The key is matched against a key in storage whenever information is stored, or whenever information is fetched from a location that is protected against fetching.