Texas Instruments TMS320C6726, TMS320C6727, TMS320C6722 warranty Enhanced C67x+ CPU, CPU Data Paths

TMS320C6727, TMS320C6726, TMS320C6722

Floating-Point Digital Signal Processors

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SPRS268E –MAY 2005 –REVISED JANUARY 2007

2.2 Enhanced C67x+ CPU

The TMS320C672x floating-point digital signal processors are based on the new C67x+ CPU. This core is code-compatible with the C67x CPU core used on the TMS320C671x DSPs, but with significant enhancements including an increase in core operating frequency from 225 MHz to 300 MHz(2) while operating at 1.2 V.

The CPU fetches 256-bit-wide advanced very-long instruction word (VLIW) fetch packets that are composed of variable-length execute packets. The execute packets can supply from one to eight 32-bit instructions to the eight functional units during every clock cycle. The variable-length execute packets are a key memory-saving feature, distinguishing the C67x CPU from other VLIW architectures. Additionally, execute packets can now span fetch packets, providing a code size improvement over the C67x CPU core.

The CPU features two data paths, shown in Figure 2-1, each composed of four functional units (.D, .M, .S, and .L) and a register file. The .D unit in each data path is a data-addressing unit that is responsible for all data transfers between the register files and the memory. The .M functional units are dedicated for multiplies, and the .S and .L functional units perform a general set of arithmetic, logical, and branch functions. All instructions operate on registers as opposed to data in memory, but results stored in the 32-bit registers can be subsequently moved to memory as bytes, half-words, or words.

Data Path A

Register File A

Cross Paths

Data Path B

Register File B

.D1

.M1

.S1

.L1

.D2

.M2

.S2

.L2

Figure 2-1. CPU Data Paths

The register file in each data path contains 32 32-bit registers for a total of 64 general-purpose registers. This doubles the number of registers found on the C67x CPU core, allowing the optimizing C compiler to pipeline more complex loops by decreasing register pressure significantly.

The four functional units in each data path of the CPU can freely share the 32 registers belonging to that data path. Each data path also features a single cross path connected to the register file on the opposing data path. This allows each data path to source one cross-path operand per cycle from the opposing register file. On the C67x+ CPU, this single cross-path operand can be used by two functional units per cycle, an improvement over the C67x CPU in which only one functional unit could use the cross-path operand. In addition, the cross-path register read(s) are not counted as part of the limit of four reads of the same register in a single cycle.

The C67x+ CPU executes all C67x instructions plus new floating-point instructions to improve performance specifically during audio processing. These new instructions are listed in Table 2-2.

(2)CPU speed is device-dependent. See Table 2-1.

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