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: YosysHQ/apicula#177