Microsemi SmartFusion2 - Page 98

Cortex-M3 Processor (Reference Material)
UG0331 User Guide Revision 15.0 64
happens in order of increasing register numbers, with the lowest numbered register using the lowest
memory address and the highest number register using the highest memory address. If the writeback
suffix is specified, the value of Rn + 4 * ( n -1) is written back to Rn .
For
LDMDB , LDMEA , STMDB , and STMFD the memory addresses used for the accesses are at 4-byte
intervals ranging from Rn to Rn - 4 * ( n -1), where n is the number of registers in reglist . The accesses
happen in order of decreasing register numbers, with the highest numbered register using the highest
memory address and the lowest number register using the lowest memory address. If the writeback
suffix is specified, the value of
Rn - 4 * ( n -1) is written back to Rn .
The
PUSH and POP instructions can be expressed in this form. See PUSH and POP, page 65 for details.
3.6.4.6.3 Restrictions
In these instructions:
•
Rn must not be PC
• reglist must not contain SP
• in any
STM instruction, reglist must not contain PC
• in any LDM instruction, reglist must not contain PC if it contains LR
• reglist must not contain Rn if you specify the writeback suffix.
When PC is in reglist in an LDM 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.
3.6.4.6.4 Condition Flags
These instructions do not change the flags.
Examples
LDM R8,{R0,R2,R9} ; LDMIA is a synonym for LDM
TMDB R1!,{R3-R6,R11,R12}
Incorrect Examples
STM R5!,{R5,R4,R9} ; Value stored for R5 is unpredictable
LDM R2, {} ; There must be at least one register in the list.
3.6.4.7 PUSH and POP
Push registers onto, and pop registers off a full-descending stack.
3.6.4.7.1 Syntax
PUSH{cond} reglist
POP{cond} reglist
where:
cond is an optional condition code, see Conditional Execution, page 55.
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.
3.6.4.7.2 Operation
PUSH stores registers on the stack, with the lowest numbered register using the lowest memory address
and the highest numbered register using the highest memory address.
POP loads registers from the stack, with the lowest numbered register using the lowest memory address
and the highest numbered register using the highest memory address.