gtps1m3lSystem Macros

LCPCC-Low Address Protect Set and Restore

Use this system macro to set the low address protect hardware feature. This feature protects the first 512 bytes of storage against alteration by a program regardless of the storage key used by the program.

Format




PROTECT
Specifies if low address protect should be turned on, turned off, or restored to its previous setting.

ON
Turns on the low address protect feature.

OFF
Turns off the low address protect feature. Control register 0 is saved in the location given by the CR0SAVE parameter.

RESTORE
Restores the protect key to that given in the address contained in the CR0SAVE parameter.

It is assumed that a call to LCPCC to turn off the low address protection bit is issued with the same save area as that used by a call to LCPCC to obtain status for the low address protect bit.

It is assumed that an LCPCC call was issued turning off the low address protection bit, using the same save area as the LCPCC call that obtained the low address protect status.

The low address protect bit is retrieved from CR0SAVE and loaded into control register 0. The other bits in the control register are unchanged. If other bits were modified in control register 0 between when LCPCC PROTECT=OFF was issued and when LCPCC PROTECT=RESTORE was issued, these bits are not be affected by this macro.

CR0SAVE=label
This label must refer to a 5-byte area beginning on a fullword boundary. It is used to save control register 0 when PROTECT=ON or PROTECT=OFF as well as to restore bit 3 of control register 0 when PROTECT=RESTORE.

Entry Requirements

E-type programs must be in supervisor state to run this macro. This requires a MONTC call and authorization to use it through correct program allocation.

Return Conditions

None.

Programming Considerations

Examples