Verify that only bank 14 I/O pins are functional on xc7k325tffg676-1 (QMTech)

[unbtorsten]

Based on observations in #7 and #8, we should be able to find unusable I/O on the QMTech board. @hansfbaier do you have schematics for the board and how it connects the I/O to the FPGA banks? A single example of an I/O that is not on bank 14 would prove the point. Also, is your proof-of-concept example using exclusively bank 14?

[hansfbaier]

https://github.com/ChinaQMTECH/QMTECH_XC7K325T_CORE_BOARD

[unbtorsten]

Thank you for the link. U11D on page 2 confirms that system clock and LEDs are indeed connected to bank 14:

The QMTech example is currently using pins F22 and J26, cf. https://github.com/kintex-chatter/xc7k325t-blinky-nextpnr/blob/main/blinky-qmtech.xdc)

[unbtorsten]

I modified the blinky design to be

module blinky (
    input aux,
    output led
    );

    assign led = aux;
endmodule

Interestingly, I seem to be able to place various I/O from e.g. banks 13 (pin R22), bank 15 (pin C16), or bank 16 (pin A9) with constraints such as these:

set_property LOC R22 [get_ports aux]
set_property IOSTANDARD LVCMOS33 [get_ports {aux}]

However, these pins are PCB-internal.

On the other hand, if I connect switch SW2 (connected to bank 33)

set_property LOC AF9 [get_ports aux]
set_property IOSTANDARD LVCMOS33 [get_ports {aux}]

I get the previously known pattern of an assertion failure:

terminate called after throwing an instance of 'nextpnr_xilinx::assertion_failure'
  what():  Assertion failure: s != -1 (nextpnr-xilinx/xilinx/arch.h:1602)
./makeit.sh: line 26: 273163 Aborted                 nextpnr-xilinx --chipdb ${CHIPDB_DIR}/${PART}.bin --xdc ${PROJECT_NAME}-${BOARD}.xdc --json ${PROJECT_NAME}.json --write ${PROJECT_NAME}_routed.json --fasm ${PROJECT_NAME}.fasm --verbose --debug

This supports @jrrk2's hypothesis and the discussion in #8.

[unbtorsten]

Questions answered, continue further discussion in #8.