ARM Cortex A9 - Page 118

Level 1 Memory System
ARM DDI 0388I Copyright © 2008-2012 ARM. All rights reserved. 7-7
ID073015 Non-Confidential
Return stack predictions
The return stack stores the address and the instruction execution state of the instruction after a
function-call type branch instruction. This address is equal to the link register value stored in
r14. The following instructions cause a return stack push if predicted:
•
BL immediate
•
BLX(1) immediate
•
BLX(2) register
•
HBL (ThumbEE state)
•
HBLP (ThumbEE state).
The following instructions cause a return stack pop if predicted:
•
BX r14
• MOV pc, r14
• LDM r13, {…pc}
• LDR pc, [r13] .
The
LDR instruction can use any of the addressing modes, as long as r13 is the base register.
Additionally, in ThumbEE state you can also use r9 as a stack pointer so the
LDR and LDM
instructions with pc as a destination and r9 as a base register are also treated as a return stack
pop.
Because return-from-exception instructions can change processor privilege mode and security
state, they are not predicted. This includes the
LDM(3) instruction, and the MOVS pc, r14
instruction.