Vigiair / wifibroadcast

tinkering with befinitiv's wifibroadcast project

tinkering with befinitiv's wifibroadcast project

• (send video thru 802.11 STA via packet injection, for RC FPV)
• https://bitbucket.org/befi/wifibroadcast
• https://befinitiv.wordpress.com/

##Added Features

• careful backoff and retry when adapter falls behind pcap_inject()
• enhanced timing stats (instantaneous and average kbps, mbit/s)
• a driver that runtime patches ath9k_htc driver, the ath fw (work in progress)
  • fw patch at fw load to insert new rate
  • driver patch to up tx power to 30db
  • change internal chipset register values for max throughput

##How Does WifiBroadcast Work?

• raspbian comes with a utility that reads video: raspivid
• raspivid's output gets piped into the tx portion of this project

##Steps

• install libpcap sudo apt-get install libpcap-dev
• install iw sudo apt-get install iw
• patch firmware sudo cp ./patches/AR9271/firmware/htc_9271.fw over /lib/firmware/htc_9271.fw
• compile lib ilclient cd /opt/vc/src/libs/ilclient && make
• compile hello_video cd /opt/vc/src/hello_video && make
• compile wifibroadcast cd <wifibroadcast_dir> && make
• remove avahi-daemon sudo apt-get remove avahi-daemon
• kill other interface meddling processes pkill dhcpcd pkill ntpd
• run it ./tx or ./rx (see ./scripts/tx.sh for example)
  • ifconfig wlan0 down
  • iw dev wlan0 set monitor otherbss fcsfail
  • ifconfig wlan0 up
  • iwconfig wlan0 channel 11
• setup auto start (see ./scripts/systemd)

##Other Notes ###testing in linux mplayer can play h264 from stdin: mplayer - -fps 48 (or whatever $FPS is defined in the scripts)

###getting .config from running raspi board

sudo modprobe configs
zcat /proc/config.gz

###testing the TL-WN722N (AR9271 Rev:1) in Ubuntu

ifconfig wlan0 down
iw dev wlan0 set monitor otherbss fcsfail
ifconfig wlan0 up
iwconfig wlan0 channel 11

and now verify packets using tcpdump or wireshark

###mounting partitions within raspi images

• fdisk -l TX_2015-09-24-raspbian-jessie.img (should show FAT boot and Linux/ext4 system)
• example:

                                              Device Boot      Start         End      Blocks   Id  System
/home/a/Downloads/TX_2015-09-24-raspbian-jessie.img1            8192      122879       57344    c  W95 FAT32 (LBA)
/home/a/Downloads/TX_2015-09-24-raspbian-jessie.img2          122880     8447999     4162560   83  Linux

• Start/End/Blocks are in 512-byte units, so multiply to get file offset (8192512 and 122880512)
• mount -v -o offset=4194304 -t vfat whatever.img /mnt/raspi_boot
• mount -v -o offset=62914560 -t ext4 whatever.img /mnt/raspi_system