DSP Core Reference Manual

A-372 SC140 DSP Core Reference Manual

RTSD

RTSD Return From Subroutine With Delay Slot (AGU) RTSD

Description

Status and Conditions that Affect Instruction

Status and Conditions Changed by Instruction

None.

Example

rtsd

Operation Assembler Syntax

If (RAS valid), then RAS → PC;

else (SP – 8) → PC;

always SP – 8 → SP

RTSD

Returns from a subroutine after executing the execution set in the delay slot. If the RAS is valid, the PC is

restored from the RAS. Otherwise, the PC is popped from the active stack in memory as a 32-bit long

word. The implicit pop is done before the execution set in the delay slot is executed. The stack pointer

always decrements by 8, RAS becomes invalid, and program execution continues at the address specified

in the PC.

Note: Because RTSD uses the RAS mechanism, returning from an exception using RTSD is illegal. The

result is undefined.

SR[18] EXP Determines which stack pointer is used.

Instruction Comment

Initially ESP = $2000

jsr SUB Jump to subroutine at SUB.

- - - Skip over these instructions.

SUB MOVE.w #$20,d1 Execute the subroutine here. PC and SR pushed onto the

stack at $2000 and $2004.

- - -

rtsd move.w #$47,d9

inc d9

Execute the $47 to d9 and increment d9 to $48, the instruc-

tion in the delay slot. Return from the subroutine. PC and

SR popped from the stack.