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THUMB INSTRUCTION SET S3C2440A RISC MICROPROCESSOR
4-30
FORMAT 13: ADD OFFSET TO STACK POINTER
[6:0] 7-bit Immediate Value
[7] Sign Flag
0 = Offset is positive
1 = Offset is negative
15 0
1
14
10
01
13 12
11
SWord 7
1 0 0
78
9
6
00S
Figure 4-14. Format 13
OPERATION
This instruction adds a 9-bit signed constant to the stack pointer. The following table shows the THUMB assembler
syntax.
Table 4-14. The ADD SP Instruction
L THUMB assembler ARM equivalent Description
0 ADD SP, #Imm ADD R13, R13, #Imm Add #Imm to the stack pointer (SP).
1 ADD SP, # -Imm SUB R13, R13, #Imm Add #-Imm to the stack pointer (SP).
NOTE
The offset specified by #Imm can be up to -/+ 508, but must be word-aligned (ie with bits 1:0 set to 0)
since the assembler converts #Imm to an 8-bit sign + magnitude number before placing it in field SWord7.
The condition codes are not set by this instruction.
INSTRUCTION CYCLE TIMES
All instructions in this format have an equivalent ARM instruction as shown in Table 4-14. The instruction cycle
times for the THUMB instruction are identical to that of the equivalent ARM instruction.
EXAMPLES
ADD SP, #268 ; SP (R13) := SP + 268, but don't set the condition codes.
Note that the THUMB opcode will contain 67 as the
Word7 value and S=0.
ADD SP, #-104 SP (R13) := SP - 104, but don't set the condition codes.
; Note that the THUMB opcode will contain 26 as the
Word7 value and S=1.