loading firmware over serial
$ lxterm --kernel firmware/firmware.bin /dev/cu.usbserial-A600K743
$ litex_server --uart --uart-port /dev/cu.usbserial-142401 --uart-baudrate 3000000
$ lxterm --kernel ../firmware/firmware.bin crossover
$ litex_server --uart --uart-port /dev/cu.usbserial-142401 --uart-baudrate 3000000
$ (cd build; litescope_cli)
$ (cd build; litescope_cli -f ps2_keyboard_clk)
$ wishbone-tool --serial /dev/cu.usbserial-142401 --baud 3000000 -s gdb
$ riscv64-unknown-elf-gdb firmware.elf -ex 'target remote localhost:3333'