Samsung S3C2440A - Manual (Page 122)

S3C2440A RISC MICROPROCESSOR THUMB INSTRUCTION SET
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THUMB INSTRUCTION SET
THUMB INSTRUCTION SET FORMAT
The thumb instruction sets are 16-bit versions of ARM instruction sets (32-bit format). The ARM instructions are
reduced to 16-bit versions.Thumb instructions, at the cost of versatile functions of the ARM instruction sets. The
thumb instructions are decompressed to the ARM instructions by the Thumb decompressor inside the ARM920T
core.
As the Thumb instructions are compressed ARM instructions, the Thumb instructions have the 16-bit format
instructions and have some restrictions. The restriction by 16-bit format is fully notified for using the Thumb
instructions.