json2dcp: replace deprecated RapidWright API; fix cell placement and routing

[hansemro]

json2dcp has not been maintained for some time but could be useful for post-placement/routing validation and DRC in Vivado. While replacing deprecated RapidWright API is fairly straightforward, it will be less trivial to fix json2dcp to handle a post-route netlist json file produced with more recent versions of nextpnr-xilinx.

From what I have experimented so far, the following needs work:

• IOB PAD/IBUF/OBUF cell instantiation/placement and routing
  • createAndPlaceIOB should be used to create IBUF/OBUF cells but require specifying IOSTANDARD and PACKAGE_PIN attributes which are retained in PAD cells.
  • Need to investigate how to configure IOB sites for differential IO pins
• inter-site and intra-site net/PIP routing
  • In general, when handling intra-site (SITEWIRE/<SITE>/<SRCNET> to SITEWIRE/<SITE>/<SNKNET>) routing, we can use routeIntraSiteNet
  • Inter-site/tile routing involves defining a set of PIPs that establishes a routed net
• Enhancement: ingest a post-placement netlist, skip routing processing, and produce DCP with just cell placement.
  • This could be useful for testing routing feasibility using Vivado's router as we test with more congested designs.

Experimental branch: https://github.com/hansemro/nextpnr-xilinx/commits/rapidwright-2024.1.0/

• Tested RapidWright commit: https://github.com/Xilinx/RapidWright/commits/1432ed645b129225f4af1f7111b1fa3d28511e02
• GSON 2.11.0: https://github.com/google/gson/releases/tag/gson-parent-2.11.0
• Currently does not yet handle IOB cells properly so designs with them will fail...
  • json2dcp should be able to process primitive-tests/clb-tests/jtag-test without debug LEDs.
• To enable json2dcp build, specify the following cmake options: -DRAPIDWRIGHT_PATH=/path/to/RapidWright -DGSON_PATH=/path/to/gson.jar

[hansemro]

Ported json2dcp to python jupyter notebook with IOB PAD/IBUF/OBUF and routing handling improvements: https://github.com/hansemro/json2dcp-notebook/blob/main/json2dcp.ipynb

This should hopefully help out anyone interested in experimenting with this work.

[hansemro]

Experimental branch with inter-site/tile net routing: https://github.com/hansemro/json2dcp-notebook/tree/inter-site-routing-dev

Partially routed jtag-test design:

Now focusing on identifying remaining routing and DRC issues...

[hansemro]

Currently, createIBUFDS only supports Ultrascale series with DIFFINBUF+IBUFCTRL BELs, so we will need to find a different way to support 7 series.

[hansemro]

I am seeing some bogus PIPs in the nextpnr netlist:

• incorrect INT tile name for GND_WIRE and VCC_WIRE routing nodes (from TIEOFF sites)
  • Example of invalid PIP: INT_L_X0Y134/VCC_WIRE->INT_R_X25Y134/FAN_ALT7
    • Note that the horizontal position is off (and possibly why the prefix between source and sink tiles do not match)
    • Incorrect position may have derived from the following: NULL_X0Y260/PSEUDO_VCC_WIRE_GLBL->INT_L_X0Y134/VCC_WIRE
  • json2dcp workaround: use sink tile name when retrieving source GND_WIRE/VCC_WIRE routing nodes.
    • https://github.com/hansemro/json2dcp-notebook/commit/a7a449749867ce40497cbd8b8b6565a21b0ffba5
• invalid site pin destination in some CLB tile to site routings:
  • Bogus PIP (D5 != D1): CLBLM_R_X25Y133/CLBLM_M_D5->SITEWIRE/SLICE_X36Y133/D1

clb jtag test json netlist: https://gist.github.com/hansemro/dea2b6b9eac13566f113f7a91474b5d1

Currently, createIBUFDS only supports Ultrascale series with DIFFINBUF+IBUFCTRL BELs, so we will need to find a different way to support 7 series.

IBUFDS support for 7 series being experimented in https://gist.github.com/hansemro/24adef209d9ff91f2c01b6f053990861

[hansemro]

Finally got around to handling IBUFDS in https://github.com/hansemro/json2dcp-notebook/commit/9a41b8296c2e49593eaddbc3cd49eaad1034fa92.