Texas Instruments TMS320C67X/C67X+ DSP manual Addressing Modes, Linear Addressing Mode

Addressing Modes

3.8 Addressing Modes

The addressing modes on the C67x DSP are linear, circular using BK0, and circular using BK1. The addressing mode is specified by the addressing mode register (AMR), described in section 2.7.3.

All registers can perform linear addressing. Only eight registers can perform circular addressing: A4−A7 are used by the .D1 unit and B4−B7 are used by the .D2 unit. No other units can perform circular addressing. LDB(U)/LDH(U)/LDW, STB/STH/STW, ADDAB/ADDAH/ADDAW/ADDAD, and SUBAB/SUBAH/SUBAW instructions all use AMR to determine what type of address calculations are performed for these registers.

3.8.1Linear Addressing Mode

3.8.1.1LD and ST Instructions

For load and store instructions, linear mode simply shifts the offsetR/cst operand to the left by 3, 2, 1, or 0 for doubleword, word, halfword, or byte access, respectively; and then performs an add or a subtract to baseR (depending on the operation specified).

For the preincrement, predecrement, positive offset, and negative offset address generation options, the result of the calculation is the address to be accessed in memory. For postincrement or postdecrement addressing, the value of baseR before the addition or subtraction is the address to be accessed from memory.

3.8.1.2ADDA and SUBA Instructions

For integer addition and subtraction instructions, linear mode simply shifts the src1/cst operand to the left by 3, 2, 1, or 0 for doubleword, word, halfword, or byte data sizes, respectively, and then performs the add or subtract specified.

3-30 Instruction Set SPRU733