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assemblyaddressing-mode

Indirect addressing with + and []

Im a bit new to the asm stuff. Looking through asm generated from C for TI's C28x CPU and have the instruction 

MOVL *+XAR4[0],ACC

I know its a long operand move instruction that takes the value in the accumulator and puts it in the location pointed at by.... what?

XAR4 is auxiliary register 4 but what does the '+' and '[0]' do? Will they take extra cycles?

Solution

  • From section 5.6 "Indirect Addressing Modes" of the "TMS320C28x DSP CPU and Instruction Set Reference Guide":

    *+XARn[3bit]
32bitDataAddr(31:0) = XARn + 3bit
Note: The immediate value is treated as an unsigned 3-bit value.

    So it will store ACC at the memory location pointed to by XAR4 (XAR4+0 to be specific).

    When the 3-bit offset is 0 it's possible to leave it out:

    The assembler also accepts ”*XARn” as an addressing mode.
This is the same encoding as the ”*+XARn[0]” mode