Features and Functional Modes

The DSP Engine can operate in a number of functional modes. Some highlights of the functionality include:

• 27 × 24 + 58 two’s complement multiply-accumulator with 27-bit pre-addition and optional product negation.
• 18 × 18 + 58 two’s complement complex multiply-accumulator using two back-to-back DSP58s, each of the two complex inputs can be optionally conjugated.
• Single-precision floating-point (binary32) accumulation.
• Mixed-precision floating-point multiply-accumulator with multiplicand and multiplier statically and independently selectable to be either binary16 or binary32, and binary32 biasing and accumulation.
• Three-element two’s complement vector dot product with accumulate or post-add in INT8 mode.
• Power saving 27-bit pre-adder that optimizes symmetrical filter applications and reduces DSP logic requirements.
• 58-bit accumulator that can be cascaded to build 116-bit and larger accumulators, adders, and counters.
• Single-instruction-multiple-data (SIMD) arithmetic unit with dual 24-bit or quad 12-bit add/subtract/accumulate.
• 58-bit logic unit: bitwise AND, OR, NOT, NAND, NOR, XOR, and XNOR.
• Pattern detector: terminal counts, overflow/underflow, convergent/symmetric rounding support, and 116-bit wide AND/NOR when combined with logic unit to detect if output matches a pattern.
• Optional pipeline registers and dedicated buses for cascading multiple DSP58s in a column for hierarchical/composite functions such as systolic FIR filters.

The new CLB contains exactly 50% LUTRAM/SRL capable LUTs to provide single port distributed SRAMs to the DSP. This structure can be replicated through the device to maximize ease of timing closure.

Figure 1. Two Back-to-Back DSP58 Supertiles

The two back-to-back DSP58s form one complex arithmetic unit with their DSP_MODE attributes set to CINT18 (see the following figure). The right DSP58 in a dual-DSP58 complex arithmetic unit computes the real result P_RE. Concurrently, the left DSP58 computes the imaginary result P_IM. Shared signals (for example, CLK and ASYNC_RST) are routed only to the interconnect interface of the left DSP58.

Figure 2. One DSP58 Complex Mode Supertile

Details on the various functional modes are provided in the following chapters.