ECP5: Replicate OE FF for each output bit #578
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nextpnr can only pack OE FFs into IOLOGIC when there's one OFS1P3DX per output, rather than one shared instance.
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Coverage 81.50% 81.50%
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Files 49 49
Lines 6461 6461
Branches 1287 1287
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Partials 187 187 Continue to review full report at Codecov.
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whitequark
approved these changes
Jan 23, 2021
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My design has a SDR 16-bit bidirectional I/O, and currently nmigen emits a single OFS1P3DX instance for the OE signal, and its output is used for all 16 BB instances. nextpnr then complains:
The problem seems to be having one instance of OFS1P3DX, which yosys marks syn_useioff, but it can't be packed because it's needed in 16 places. This PR updates
lattice_ecp5.pyto generate n OFS1P3DX for the OE (well, T) signal instead, which nextpnr does then pack into IOLOGIC successfully. I've also tried this with DDR OE outputs which were also packed successfully, so I removed that comment too.Happy to hear if you'd rather make a wider OE signal and use the normal
get_oregwith it instead, or anything like that.