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S3C2440A RISC MICROPROCESSOR THUMB INSTRUCTION SET
4-37
FORMAT 18: UNCONDITIONAL BRANCH
[10:0] Immediate Value
15 0
1
14
11
13 12
11
Offset11
0
10
0
Figure 4-19. Format 18
OPERATION
This instruction performs a PC-relative Branch. The THUMB assembler syntax is shown below. The branch offset
must take account of the prefetch operation, which causes the PC to be 1 word (4 bytes) ahead of the current
instruction.
Table 4-19. Summary of Branch Instruction
THUMB assembler ARM equivalent Description
B label BAL label (halfword offset) Branch PC relative +/- Offset11 << 1, where label is
PC +/- 2048 bytes.
NOTE
The address specified by label is a full 12-bit two's complement address,
but must always be halfword aligned (ie bit 0 set to 0), since the assembler places label >> 1 in the Offset11 field.
EXAMPLES
here B here ; Branch onto itself. Assembles to 0xE7FE.
(Note effect of PC offset).
B jimmy ; Branch to 'jimmy'.
• Note that the THUMB opcode will contain the number of
•
• ; halfwords to offset.
jimmy
• Must be halfword aligned.