Use this system macro to allocate a specific number of 4 KB frames as
contiguous storage in the system heap.
Format
- label
- A symbolic name can be assigned to the macro statement.
- FRAMES=Rm
- The FRAMES parameter specifies the number of contiguous 4 KB pages to be
allocated. The general register used must be R0-R12, R14, or
R15.
- TOKEN=Rn
- The TOKEN parameter specifies the address of an 8-character string that
the TPF system uses to identify the allocated storage. The general
register used must be R0-R12, R14, or R15.
- SAVREG
- The specified volatile registers will be saved by the macro in
the stack area or in the registers specified by the WKREG parameter. Up
to 3 registers can be specified. Those registers are R0, R1, R2.
If this keyword is omitted, none of the 3 registers will be saved. You
should not save a volatile register if you expect it to contain an output
parameter. The register will be overwritten with its original contents,
since the reload is the last thing performed by the macro.
- WKREG
- The specified symbolic register names are free to be used by the macro to
save the volatile registers coded on the SAVREG parameter.
Up to 3 registers can be specified, but the standard linkage registers R13
through R2 cannot be used here. This parameter is used in conjunction
with the SAVREG parameter to generate efficient code and enhance the
performance of the macro. The number of registers specified by WKREG
should be less than or equal to the number of registers specified by
SAVREG. If this parameter is omitted or not used to its maximum
capacity, code optimization is sacrificed.
Entry Requirements
- This macro is for use in the control program (CP) only while running in
key 0 and supervisor state.
- You can use this macro in entry control block (ECB) virtual memory (EVM)
or system virtual memory (SVM) address modes.
Return Conditions
- The register specified by FRAMES contains the starting address of the
allocated storage.
- The register specified by FRAMES contains 0 if:
- The FRAMES parameter register contains zero.
- The system heap does not contain enough storage to satisfy the allocation
request.
- The address specified by the TOKEN parameter is not in the range of
addressable memory.
- Control is not returned if there is not enough real storage to satisfy the
request. The TPF system issues an error and recovers through an
automatic IPL.
Programming Considerations
- This macro is restricted to CP use only.
- Real storage may not be contiguous.
- The amount of virtual storage available for the system heap is defined in
CTKA.
- Storage acquired must be released by the RSYSC or $RSYSC macro
when it is no longer needed. If the storage is not released, it remains
in use until you IPL the TPF system again.
- The address returned is a 31-bit address.
- The storage key is set to X'C'.
Examples
The following example shows how the length of a block is converted into a
number of 4 KB frames before requesting storage from the system heap.
The return code is checked before trying to use the address in R14.
ITUUTL REG1=R14 CONNECT WITH TABLE UPDATE DSECT
LA R14,ITULEN GET THE LENGTH OF A BLOCK
LA R14,4095(R14) ROUND TO THE NEXT 4 KB
LR R7,R14 SAVE NUMBER OF FRAMES
SRL R14,12 DETERMINE NUMBER OF 4 KB FRAMES
LA R6,MY_TABLE
$GSYSC FRAMES=R14,TOKEN=R6 ALLOCATE THE STORAGE
LTR R14,R14 CHECK THE RETURN CODE
BZ NO_STORAGE_AVAIL BRANCH TO PROCESS ERROR
.
.
routine that uses the storage
.
.
RELEASE_STORAGE DS 0H
LA R6,MY_TABLE
$RSYSC ADDRESS=R14,FRAMES=R7,TOKEN=R6 RELEASE THE STORAGE
LTR R15,R15 CHECK THE RETURN CODE
BNZ RELEASE_ERROR BRANCH TO PROCESS ERROR
.
.
.
.
MY_TABLE DC CL8'MY_TABLE'