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YosysHQ / nextpnr

nextpnr portable FPGA place and route tool
ISC License
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ECP5: Add support for REGMODE parameters on DP16KD #422

Closed rschlaikjer closed 4 years ago

rschlaikjer commented 4 years ago

When manually instantiating the DP16KD primitive with the REGMODE_A or REGMODE_B parameter set to OUTREG, the value is ignored and the DP16KD is instantiated as though the register mode was still set to the default (unregistered). This results in a propagation delay for the bram of 5.8ns, compared to the expected 0.95ns for a bram with registered output.

Sample instantiation that exhibits the problem: https://gist.github.com/rschlaikjer/37e605571beb1a9ca0b0700328aa76ec

Sample timing output: https://gist.github.com/rschlaikjer/720d2755b7fcb432b1ef652bffdc8787

rschlaikjer commented 4 years ago

PR for this here: https://github.com/YosysHQ/nextpnr/pull/423