nextpnr-gowin cannot route OSER10 to ELVDS_OBUF

[marsohod4you]

I am trying to use oss-cad-suite (oss-cad-suite-linux-x64-20230502.tgz) building projects for GoWIn chip. Issue is I cannot use OSER10 with ELVDS_OBUF (on IO pins which are not TLVDS).

Reproduce is easy: 1) git clone https://github.com/YosysHQ/apicula.git 2) cd apicula/examples/deser 3) For simplicity I modify oser10-tlvds.v and set number of channels to 1: `define CH 1 4) Try original project with commands: yosys -p "read_verilog oser10-tlvds.v; synth_gowin -json deser-oser10-tlvds-tec0117-synth.json" nextpnr-gowin --json deser-oser10-tlvds-tec0117-synth.json --write deser-oser10-tlvds-tec0117.json --device GW1NR-UV9QN88C6/I5 --cst oser10-tlvds-tec0117.cst gowin_pack -d GW1N-9 -o deser-oser10-tlvds-tec0117.fs deser-oser10-tlvds-tec0117.json

Those above commands seem work properly.

5) Now try to migrate other IO pins which do not support True LVDS by editing assignment file oser10-tlvds-tec0117.cst: //IO_LOC "q_o[0]" 29; //IO_PORT "q_o[0]" IO_TYPE=LVCMOS33; //IO_LOC "q_o[1]" 30; //IO_PORT "q_o[1]" IO_TYPE=LVCMOS33; IO_LOC "q_o[0]" 80; IO_PORT "q_o[0]" IO_TYPE=LVCMOS33; IO_LOC "q_o[1]" 79; IO_PORT "q_o[1]" IO_TYPE=LVCMOS33;

So migrate from IO pins 29,30 to 80,79. Those 80 and 79 are not true LVDS but can work as ELVDS (emulated LVDS) And also additionally edit oser10-tlvds.v file replacing TLVDS_OBUF with ELVDS_OBUF

6) Try to build with above minimal changes: yosys works properly but nextpnr-gowin crashes:

** nextpnr-gowin --json deser-oser10-tlvds-tec0117-synth.json --write deser-oser10-tlvds-tec0117.json --device GW1NR-UV9QN88C6/I5 --cst oser10-tlvds-tec0117.cst /home/nick/fpga/oss-cad-suite/bin/nextpnr-gowin: line 22: /home/nick/.config/yosyshq/fonts.conf: No such file or directory Info: Series:GW1N-9 Device:GW1NR-9 Package:QFN88 Speed:C6/I5 Info: Cell sd_out not found Info: Cell sd_out not found Info: Cell q_o[2] not found Info: Cell q_o[2] not found Info: Cell q_o[3] not found Info: Cell q_o[3] not found

Info: Packing constants.. Info: Packing Shadow RAM.. Info: Packing GSR.. Info: Packing IOs.. Info: Packing diff IOs.. Info: Packing IO logic.. terminate called after throwing an instance of 'nextpnr_gowin::assertion_failure' what(): Assertion failure: q0_dst != nullptr (/work/_builds/linux-x64/nextpnr-gowin/nextpnr/gowin/pack.cc:919) Aborted (core dumped) **

Is it possible to fix somehow? GoWin EDA builds project properly but I do not like GoWin EDA and want oss-cad-suite.

[mole99]

ELVDS is not supported yet, but afaik it is being worked on 🙂️

[mole99]

This is what your are waiting for: https://github.com/YosysHQ/apicula/pull/177