$ litex-boards/litex_boards/targets/lambdaconcept_ecpix5.py --build \
                 --cpu-type rocket --cpu-variant linuxd --sys-clk-freq 50e6 \
                 --with-ethernet --with-sdcard
[...]
INFO:SoCIRQHandler:ethmac IRQ allocated at Location 2.
INFO:SoCDMABusHandler:sdblock2mem added as Bus Master.
INFO:SoCDMABusHandler:sdmem2block added as Bus Master.
INFO:SoCIRQHandler:sdirq IRQ allocated at Location 3.
Traceback (most recent call last):
  File "/home/somlo/LITEX/litex-boards/litex_boards/targets/lambdaconcept_ecpix5.py", line 268, in <module>
    main()
  File "/home/somlo/LITEX/litex-boards/litex_boards/targets/lambdaconcept_ecpix5.py", line 257, in main
    builder.build(**trellis_argdict(args))
  File "/home/somlo/LITEX/litex/litex/build/lattice/trellis.py", line 260, in trellis_argdict
    "freq":         float(args.ecppack_freq),
TypeError: float() argument must be a string or a real number, not 'NoneType'