3.1.3.2 DSP MAC Indirect Addressing Modes

A special class of Indirect Addressing modes is utilized by the DSP MAC instructions. As is described later in DSP MAC Instructions, the DSP MAC class of instructions is capable of performing two fetches from memory using Effective Addressing. Since DSP algorithms frequently demand a broader range of address updates, the addressing modes offered by the DSP MAC instructions provide greater range in the size of the Effective Address update which may be made. The following table shows that both X and Y prefetches support Post-Increment and Post-Decrement Addressing modes with updates of two, four and six bytes. Since DSP instructions only execute in Word/Long-word mode, no provisions are made for odd-sized EA updates.

Table 3-3. DSP MAC Indirect Addressing Modes
Addressing Mode Word-ModeLong-Word Mode
X MemoryY Memory X MemoryY Memory
Indirect with No Modification EA = [Wx] EA = [Wy]EA = [Wx] EA = [Wy]
Indirect with Post-Increment by two EA = [Wx] + = 2 EA = [Wy] + = 2EA = [Wx] + = 4 EA = [Wy] + = 4
Indirect with Post-Increment by four EA = [Wx] + = 4 EA = [Wy] + = 4EA = [Wx] + = 8EA = [Wy] + = 8
Indirect with Post-Increment by six EA = [Wx] + = 6 EA = [Wy] + = 6EA = [Wx] + = 12EA = [Wy] + = 12
Indirect with Post-Decrement by two EA = [Wx] – = 2 EA = [Wy] – = 2EA = [Wx] – = 4 EA = [Wy] – = 4
Indirect with Post-Decrement by four EA = [Wx] – = 4 EA = [Wy] – = 4EA = [Wx] – = 8EA = [Wy] – = 8
Indirect with Post-Decrement by six EA = [Wx] – = 6 EA = [Wy] – = 6EA = [Wx] – = 12EA = [Wy] – = 12
Indirect with Register Offset EA = [W9 + W12] EA = [W11 + W12]EA = [W9 + W12] EA = [W11 + W12]