nextpnr-xilinx crash when using 1.8V input pin on a Kintex 7 325T fpga

[infphyny]

I have made a simple blinky example for a xc7k325tffg676-1 fpga with a reset input on a pin with constraint IOSTANDARD LVCMOS18 . The reset input is located at pin AF9 . A repro can be provided upon request.
If I remove the reset pin, I can generate bitstream and program successfully fpga.

The output of nextpnr-xilinx is:

nextpnr-xilinx -r --chipdb /usr/local/share/nextpnr/xilinx-chipdb/xc7k325tffg676-1.bin --xdc data/constraints.xdc --json blinky.json --write blinky_routed.json --fasm blinky.fasm --freq 50
Info: Packing constants..
Info: Inserting IO buffers..
Info:     IO port 'i_clock_50MHz' driven by IBUF '$iopadmap$Top.i_clock_50MHz'
Info:     IO port 'i_reset_n' driven by IBUF '$iopadmap$Top.i_reset_n'
Info:     IO port 'o_leds[0]' driven by OBUF '$iopadmap$Top.o_leds'
Info:     IO port 'o_leds[1]' driven by OBUF '$iopadmap$Top.o_leds_1'
Info:     IO port 'o_leds[2]' driven by OBUF '$iopadmap$Top.o_leds_2'
Info:     Constraining 'i_clock_50MHz' to site 'IOB_X0Y126'
Info:     Constraining 'i_reset_n' to site 'IOB_X1Y51'
Info:     Constraining 'o_leds[0]' to site 'IOB_X0Y114'
Info:     Constraining 'o_leds[1]' to site 'IOB_X0Y113'
Info:     Constraining 'o_leds[2]' to site 'IOB_X0Y231'
Info: Generating input buffer for '$iopadmap$Top.i_clock_50MHz'
Info: Generating input buffer for '$iopadmap$Top.i_reset_n'
terminate called after throwing an instance of 'nextpnr_xilinx::assertion_failure'
  what():  Assertion failure: s != -1 (/nextpnr-xilinx/xilinx/arch.h:1602)
make: *** [Makefile:21: blinky.fasm] Abandon (core dump créé)

The problem seem that nexpnr-xilinx automatically add "/IOB33/PAD" to all site and don't seem to check for io voltage.
Inside pack_io_xc7.cc XC7Packer::pack_io() function

pad->attrs[ctx->id("BEL")] = std::string(site + "/IOB33/PAD");

I think for pin AF9 or all other pin with 1.8V logic level there should be code like this :

pad->attrs[ctx->id("BEL")] = std::string(site + "/IOB18/PAD");

I have added code in file pack_io_xc7.cc to print additional information to show the site and pad attribute information. here is the output for pin AF9 with 1.8V io :

pack_io_xc7.cc::pack_io LOC: AF9
Pin name: AF9
pack_io_xc7.cc::pack_io SITE: IOB_X1Y51
Info:     Constraining 'i_reset_n' to site 'IOB_X1Y51'
pack_io_xc7.cc::pack_io pad->attrs[ctx->id("BEL")] : IOB_X1Y51/IOB33/PAD

Then in the file prjxray-db/kintex7/xc7k325t/tilegrid.json For pin AF9 at site IOB_X1Y51 is defined as

tilegrid.json:1331353:            "IOB_X1Y51": "IO_L24N_T3_33",
tilegrid.json:1331358:            "IOB_X1Y51": "IOB18S",

Here are the other 3.3V pins for comparison that nextpnr-xilinx place successfully.

Pin i_clock_50MHz at site IOB_X0Y126:

pack_io_xc7.cc::pack_io LOC: F22
Pin name: F22
pack_io_xc7.cc::pack_io SITE: IOB_X0Y126
Info:     Constraining 'i_clock_50MHz' to site 'IOB_X0Y126'
pack_io_xc7.cc::pack_io pad->attrs[ctx->id("BEL")] : IOB_X0Y126/IOB33/PAD

Tile grid definition:

tilegrid.json:1235714:            "IOB_X0Y126": "IO_L12P_T1_MRCC_14"
tilegrid.json:1235719:            "IOB_X0Y126": "IOB33M"

---

Pin o_leds[0] at site IOB_X0Y114

pack_io_xc7.cc::pack_io LOC: J26
Pin name: J26
pack_io_xc7.cc::pack_io SITE: IOB_X0Y114
Info:     Constraining 'o_leds[0]' to site 'IOB_X0Y114'
pack_io_xc7.cc::pack_io pad->attrs[ctx->id("BEL")] : IOB_X0Y114/IOB33/PAD

Tilegrid definition:

tilegrid.json:1235576:            "IOB_X0Y114": "IO_L18P_T2_A12_D28_14"
tilegrid.json:1235581:            "IOB_X0Y114": "IOB33M"

---

Pin o_leds[1] at site IOB_X0Y113

pack_io_xc7.cc::pack_io LOC: H26
Pin name: H26
pack_io_xc7.cc::pack_io SITE: IOB_X0Y113
Info:     Constraining 'o_leds[1]' to site 'IOB_X0Y113'
pack_io_xc7.cc::pack_io pad->attrs[ctx->id("BEL")] : IOB_X0Y113/IOB33/PAD

Tilegrid definition:

tilegrid.json:1235575:            "IOB_X0Y113": "IO_L18N_T2_A11_D27_14",
tilegrid.json:1235580:            "IOB_X0Y113": "IOB33S",

---

Pin o_leds[2] at site IOB_X0Y231

pack_io_xc7.cc::pack_io LOC: A8
Pin name: A8
pack_io_xc7.cc::pack_io SITE: IOB_X0Y231
Info:     Constraining 'o_leds[2]' to site 'IOB_X0Y231'
pack_io_xc7.cc::pack_io pad->attrs[ctx->id("BEL")] : IOB_X0Y231/IOB33/PAD

Tilegrid definition

tilegrid.json:1236886:            "IOB_X0Y231": "IO_L9N_T1_DQS_16",
tilegrid.json:1236891:            "IOB_X0Y231": "IOB33S",

Thanks.