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S3C2501X
PROGRAMMER'S MODEL
2-3
2.4 INSTRUCTION LENGTH
Instructions are either 32 bits long (in ARM state) or 16 bits long (in THUMB state).
2.5 DATA
TYPES
ARM9TDMI 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.
2.6 OPERATING MODES
ARM9TDMI supports seven modes of operation:
User (usr):
The normal ARM program execution state
FIQ (fiq):
Designed to support a data transfer or channel process
IRQ (irq):
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.
Содержание S3C2501X
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Страница 275: ...MEMORY CONTROLLER S3C2501X 5 60 NOTES ...
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Страница 373: ...GDMA CONTROLLER S3C2501X 9 24 NOTES ...
Страница 435: ...I O PORTS S3C2501X 12 12 NOTES ...
Страница 463: ...ELECTRICAL DATA S3C2501X 15 6 NOTES ...