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Cycle Timings and Interlock Behavior
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 14-21
ID013010 Non-Confidential, Unrestricted Access
14.13 Load and Store Multiple instructions
This section describes the cycle timing behavior for the
LDM
,
STM
,
PUSH
, and
POP
instructions.
These instructions take multiple cycles to issue, and then use multiple memory cycles to load
and store all the registers. Because the memory datapath is 64-bits wide, two registers can be
loaded or stored on each cycle.
This section describes:
• Load and Store Multiples, other than load multiples including the PC
• Load Multiples, where the PC is in the register list on page 14-22
• Example Interlocks on page 14-22
14.13.1 Load and Store Multiples, other than load multiples including the PC
In all cases the base register,
<Rn>
, is a Very Early Reg.
Table 14-17 shows the cycle timing behavior of load and store multiples including the PC.
Note
The Cycle timing behavior that Table 14-17 shows also covers
PUSH
and
POP
instructions that
behave like store and load multiple instructions with base register write-back.
Table 14-17 Cycle timing behavior of Load and Store Multiples, other than load multiples including the PC
Example instruction Cycles
Cycles
with base
register
write-back
Memory
cycles
Result latency
(LDM)
Result latency
(base register)
First address 64-bit aligned
LDMIA <Rn>,{R1}
11 1 2 1
LDMIA <Rn>,{R1,R2}
12 1 2,2 2
LDMIA <Rn>,{R1,R2,R3}
22 2 2,2,3 2
LDMIA <Rn>,{R1,R2,R3,R4}
2 3 2 2,2,3,3 3
LDMIA <Rn>,{R1,R2,R3,R4,R5}
3 3 3 2,2,3,3,4 3
LDMIA <Rn>,{R1,R2,R3,R4,R5,R6}
3 4 3 2,2,3,3,4,4 4
LDMIA
<Rn>,{R1,R2,R3,R4,R5,R6,R7}
4 4 4 2,2,3,3,4,4,5 4
First address not 64-bit aligned
LDMIA <Rn>,{R1}
12 1 2 2
LDMIA <Rn>,{R1,R2}
22 2 2,3 2
LDMIA <Rn>,{R1,R2,R3}
23 2 2,3,3 3
LDMIA <Rn>,{R1,R2,R3,R4}
3 3 3 2,3,3,4 3
LDMIA <Rn>,{R1,R2,R3,R4,R5}
3 4 3 2,3,3,4,4 4
LDMIA <Rn>,{R1,R2,R3,R4,R5,R6}
4 4 4 2,3,3,4,4,5 4
LDMIA
<Rn>,{R1,R2,R3,R4,R5,R6,R7}
4 5 4 2,3,3,4,4,5,5 5