Semihost

Semihost is used when host implements lwip at its own, and firmware takes response of 802.11 SME/MLME, all its network frames except EAPoL frames are passed up to host.

Usage

Firmware

modify CFG_HOSTED=CONFIG_SEMI_HOSTED in sys_config_bk7231u.h.

/* Host based SDIO/USB/PCI/SPI Wifi Support */
/* fully hosted: no lwip, all mgmt located at host */
#define CONFIG_FULLY_HOSTED                               1
/* semi hosted: no lwip, all mgmt located at host */
#define CONFIG_SEMI_HOSTED                                2
/* CFG_HOSTED: 0 disabled, CONFIG_FULLY_HOSTED, CONFIG_SEMI_HOSTED */
#define CFG_HOSTED                                 CONFIG_SEMI_HOSTED

compile

$ make bk7231u -j8   # add V=1 to show verbose log

burn firmware via GUI or CLI
run firmware

It's high recommended to change the default mac address, now login into the demo board.

# mac c8478c723101                     # change mac address to c8:47:8c:72:31:01

Host

This demo only runs on Linux. MacOS may also works.

compile serial-tap

$ cd tools/semihost/serial-tap
$ cmake .
$ make

This will generate an excutable binary named serial_tun.

setup a tap device

$ sudo ./setup-tapif   # add a tap0 network adapter
$ sudo ip link set address c8:47:8c:72:31:01 dev tap0     # set tap0's mac address equals to firmware
$ sudo ./serial_tun -i tap0 -p /dev/ttyUSB0

If acts as a softap, you must change tap0's mac address the same as softap's mac address, and setup a dhcp server. For example, udhcpd can be used.

$ sudo udhcpd udhcpd.conf    # setup an dhcp server

Limitation

Now UART is used as the physical layer, and the throughput is very low due to UART's low rate.

Debug

Tools such as wireshark, tcpdump can be used to analysis packet at link layer.
TAP devices' mac address must equal to firmware's mac address