xilinx_dsp - Xilinx: pack resources into DSPs¶
- yosys> help xilinx_dsp¶
xilinx_dsp [options] [selection]
Pack input registers (A2, A1, B2, B1, C, D, AD; with optional enable/reset), pipeline registers (M; with optional enable/reset), output registers (P; with optional enable/reset), pre-adder and/or post-adder into Xilinx DSP resources. Multiply-accumulate operations using the post-adder with feedback on the 'C' input will be folded into the DSP. In this scenario only, the 'C' input can be used to override the current accumulation result with a new value, which will be added to the multiplier result to form the next accumulation result. Use of the dedicated 'PCOUT' -> 'PCIN' cascade path is detected for 'P' -> 'C' connections (optionally, where 'P' is right-shifted by 17-bits and used as an input to the post-adder -- a pattern common for summing partial products to implement wide multipliers). Limited support also exists for similar cascading for A and B using '[AB]COUT' -> '[AB]CIN'. Currently, cascade chains are limited to a maximum length of 20 cells, corresponding to the smallest Xilinx 7 Series device. This pass is a no-op if the scratchpad variable 'xilinx_dsp.multonly' is set to 1. Experimental feature: addition/subtractions less than 12 or 24 bits with the '(* use_dsp="simd" *)' attribute attached to the output wire or attached to the add/subtract operator will cause those operations to be implemented using the 'SIMD' feature of DSPs. Experimental feature: the presence of a `$ge' cell attached to the registered P output implementing the operation "(P >= <power-of-2>)" will be transformed into using the DSP48E1's pattern detector feature for overflow detection.
-family {xcup|xcu|xc7|xc6v|xc5v|xc4v|xc6s|xc3sda}
select the family to target default: xc7