S3C4510B
PROGRAMMER'S MODEL
INSTRUCTION LENGTH
Instructions are either 32 bits long (in ARM state) or 16 bits long (in THUMB state).
Data Types
ARM7TDMI supports byte (8-bit), half-word (16-bit) and word (32-bit) data types. Words must be aligned to four-
byte boundaries and half words to two-byte boundaries.
OPERATING MODES
ARM7TDMI supports seven modes of operation:
— User (usr):
— FIQ (fiq):
— IRQ (irq):
The normal ARM program execution state
Designed to support a data transfer or channel process
Used for general-purpose interrupt handling
— Supervisor (svc): Protected mode for the operating system
— Abort mode (abt): Entered after a data or instruction prefetch abort
— System (sys):
A privileged user mode for the operating system
— Undefined (und): Entered when an undefined instruction is executed
Mode changes may be made under software control, or may be brought about by external interrupts or exception
processing. Most application programs will execute in User mode. The non-user modes known as privileged
modes-are entered in order to service interrupts or exceptions, or to access protected resources.
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SAMSUNG [ SAMSUNG ]
