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ARM Load/Store Instructions

ARM Load/Store Instructions. The ARM is a Load/Store Architecture: Only load and store instructions can access memory Does not support memory to memory data processing operations. Must move data values into registers before using them. ARM Load/Store Instructions.

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ARM Load/Store Instructions

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  1. ARM Load/Store Instructions • The ARM is a Load/Store Architecture: • Only load and store instructions can access memory • Does not support memory to memory data processing operations. • Must move data values into registers before using them.

  2. ARM Load/Store Instructions • ARM has three sets of instructions which interact with main memory. These are: • Single register data transfer (LDR/STR) • Block data transfer (LDM/STM) • Single Data Swap (SWP)

  3. ARM Load/Store Instructions • The basic load and store instructions are: LDR STR Word LDRB STRB Byte LDRH STRH Halfword LDRSB Signed byte load LDRSH Signed halfwordload

  4. ARM Load/Store Instructions • Memory system must support all access sizes • Syntax: • LDR{<cond>}{<size>} Rd, <address> • STR{<cond>}{<size>} Rd, <address> e.g. LDR R0, [R1] STR R0, [R1] LDREQB R0, [R1]

  5. Data Transfer: Memory to Register (load) • To transfer a word of data, we need to specify two things: • Register: r0-r15 • Memory address: more difficult • Think of memory as a single one-dimensional array, so we can address it simply by supplying a pointer to a memory address. • There are times when we will want to offset from this pointer.

  6. ARM Addressing Modes There are basically two types of addressing modes available in ARM • Pre-indexex addressing: the address generated is used immediately • Post-indexex addressing: the address generated later replaces the base register

  7. r0 r1 DestinationRegisterfor ldr 0x5 0x200 0x200 ARM Addressing Modes . . . . .

  8. r1 188 r2 27 200 DestinationRegisterfor ldr ARM Addressing Modes . . .

  9. ARM Addressing Modes

  10. ARM Addressing Modes

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  13. ARM Addressing Modes

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