Transport Triggered Architecture - Benefits in Comparison To VLIW Architectures

Benefits in Comparison To VLIW Architectures

TTAs can be seen as "exposed datapath" VLIW architectures. While VLIW is programmed using operations, TTA splits the operation execution to multiple move operations. The low level programming model enables several benefits in comparison to the standard VLIW. For example, a TTA architecture can provide more parallelism with simpler register files than with VLIW. As the programmer is in control of the timing of the operand and result data transports, the complexity (the number of input and output ports) of the register file (RF) need not be scaled according to the worst case issue/completion scenario of the multiple parallel instructions.

An important unique software optimization enabled by the transport programming is called software bypassing. In case of software bypassing, the programmer bypasses the register file write back by moving data directly to the next functional unit's operand ports. When this optimization is applied aggressively, the original move that transports the result to the register file can be eliminated completely, thus reducing both the register file port pressure and freeing a general purpose register for other temporary variables. The reduced RF pressure, in addition simplifying the required complexity of the RF hardware, can lead to significant energy savings, an important benefit especially in mobile embedded systems.