programming-model - CSE 379 ARM Programming Model The...

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CSE 379 ARM Programming Model The Register Bank 37 Registers Registers are banked 20 of the 37 are hidden from program Mode determines which registers are visible Accessing a Register The register number is preceded by an ‘r’ Examples r0 r13 Stack Pointer User Mode Current Program Status Register (CPSR) Stores condition codes Condition Code Flags Negative (N) - Negative Result Zero (Z) - Zero Result Carry (C) - Carry Out Overflow (V) - Overflow into Sign Bit Processor Mode (Mode) Instruction Set (T) Interrupt Enables (IF) Fast or Normal r0 User Mode r1 r2 r3 r4 r5 r6 r7 r8 r8_fiq Fast Interrupt Request r9 r9_fiq r10 r10_fiq r11 r11_fiq r12 r12_fiq Interrupt Request Abort Supervisor Undefined r13 SP r13_fiq r13_irq r13_abt r13_svc r13_und r14 LR r14_fiq r14_irq r14_abt r14_svc r14_und r15 PC CPSR SPSR_fiq SPSR_irq SPSR_abt SPSR_svc SPSR_unf System Modes Only Only Usable in User Mode 28 27 8 7 6 5 4 3 2 1 0 29 30 31 C V I F T Mode Unused Z N
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User Mode vs. Supervisor Mode Supervisor Mode Protected Ensures user code cannot gain supervisor privileges without certain checks taking place to prevent code from executing illegal operations System-level functions can only be accessed through supervisor calls which typically comprise: Accesses to hardware peripheral registers
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programming-model - CSE 379 ARM Programming Model The...

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