Indirect addressing with + and []

Question

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?

Answer 1

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