Atmel SAM4S Series, Preliminary Data Sheet

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104
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
11.6.4.7 PUSH and POP
Push registers onto, and pop registers off a full-descending stack.
Syntax
PUSH{cond} reglist
POP{cond} reglist
where:
cond is an optional condition code, see “Conditional Execution” .
reglist is a non-empty list of registers, enclosed in braces. It can contain register
ranges. It must be comma separated if it contains more than one register or
register range.
PUSH and POP are synonyms for STMDB and LDM (or LDMIA) with the memory addresses for
the access based on SP, and with the final address for the access written back to the SP. PUSH
and POP are the preferred mnemonics in these cases.
Operation
PUSH stores registers on the stack in order of decreasing the register numbers, with the highest
numbered register using the highest memory address and the lowest numbered register using
the lowest memory address.
POP loads registers from the stack in order of increasing register numbers, with the lowest num-
bered register using the lowest memory address and the highest numbered register using the
highest memory address.
See “LDM and STM” for more information.
Restrictions
In these instructions:
• reglist must not contain SP
• for the PUSH instruction, reglist must not contain PC
• for the POP instruction, reglist must not contain PC if it contains LR.
When PC is in reglist in a POP instruction:
• bit[0] of the value loaded to the PC must be 1 for correct execution, and a branch occurs to
this halfword-aligned address
• if the instruction is conditional, it must be the last instruction in the IT block.
Condition Flags
These instructions do not change the flags.
Examples
PUSH {R0,R4-R7}
PUSH {R2,LR}
POP {R0,R10,PC}