This is a nice feature if you want to use QEMU to debug a NuttX board and learn more about its initialization.
Configure NuttX to use the stellaris lm3s6965-ek board with qemu-flat config:
$ ./tools/configure.sh lm3s6965-ek:qemu-flat
Run QEMU with the generated "nuttx" ELF file: $ qemu-system-arm -net nic,model=stellaris -net user,hostfwd=tcp:127.0.0.1:10023-10.0.2.15:23,hostfwd=tcp:127.0.0.1:10021-10.0.2.15:21 -M lm3s6965evb -kernel nuttx -nographic -s -S
$ arm-none-eabi-gdb -i=mi -ix=./tools/nuttx-gdbinit nuttx (gdb) target extended-remote:1234 (gdb) c
You can connect to board using telnet:
$ telnet localhost 10023
Connected to localhost.
Escape character is '^]'.
NuttShell (NSH) NuttX-10.0.1
Note: 10.0.2.15 is the internal IP of the emulated lm3s6965evb ethernet on QEMU. The hostfwd command just forward the access to the localhost port 10023 to 23 (telnet) of the emulated board. Same to port 10021 and 21 (ftp).
Note 2: You can exit QEMU pressing: Ctrl A + x