Texas Instruments TMS320C67X/C67X+ DSP manual Functional Units

Functional Units

2.3 Functional Units

The eight functional units in the C6000 data paths can be divided into two groups of four; each functional unit in one data path is almost identical to the corresponding unit in the other data path. The functional units are described in Table 2−2.

Most data lines in the CPU support 32-bit operands, and some support long (40-bit) and double word (64-bit) operands. Each functional unit has its own 32-bit write port into a general-purpose register file (Refer to Figure 2−1). All units ending in 1 (for example, .L1) write to register file A, and all units ending in 2 write to register file B. Each functional unit has two 32-bit read ports for source operands src1 and src2. Four units (.L1, .L2, .S1, and .S2) have an extra 8-bit-wide port for 40-bit long writes, as well as an 8-bit input for 40-bit long reads. Because each unit has its own 32-bit write port, when performing 32-bit operations all eight units can be used in parallel every cycle.

See Appendix B for a list of the instructions that execute on each functional unit.

Table 2−2. Functional Units and Operations Performed

Functional Unit	Fixed-Point Operations	Floating-Point Operations
.L unit (.L1, .L2)	32/40-bit arithmetic and compare operations	Arithmetic operations
	32-bit logical operations	DP → SP, INT → DP, INT → SP
	Leftmost 1 or 0 counting for 32 bits	conversion operations
	Normalization count for 32 and 40 bits
.S unit (.S1, .S2)	32-bit arithmetic operations	Compare
	32/40-bit shifts and 32-bit bit-field operations	Reciprocal and reciprocal square-root
	32-bit logical operations	operations
	Branches	Absolute value operations
		SP → DP conversion operations
	Constant generation
	Register transfers to/from control register	SPand DP adds and subtracts
	file (.S2 only)	SP and DP reverse subtracts (src2 − src1)
.M unit (.M1, .M2)	16 ⋅ 16-bit multiply operations	Floating-point multiply operations
	32 ⋅ 32-bit multiply operations	Mixed-precision multiply operations
.D unit (.D1, .D2)	32-bit add, subtract, linear and circular	Load doubleword with 5-bit constant
	address calculation	offset
	Loads and stores with 5-bit constant offset
	Loads and stores with 15-bit constant
	offset (.D2 only)

SPRU733 CPU Data Paths and Control 2-5