1. 源由

为了利用手头的树莓派硬件，同时，搭建一个Rover FPV验证平台。

前期，在《msposd 开源代码之树莓派3B+ Bookworm部署》中已经基本完成。

但是，无法显示fps/bitrate数据，初步讨论结果：

• msposd 对树莓派暂未支持，且不支持FPS/bitrate的显示

2. 分析

经过简单的初步分析，我们了解到libcamera-vid打印日志中，含有或者间接含有相关数据。

例如：

• 帧 #34
• FPS 29.99 Hz
• 数据量 21008 Bytes

计算公式：

$Bitrate(bps)=(\text{Sum of buffer sizes (bytes)}\times 8)\times \text{fps}$
$Bitrate(bps)=(\text{21008 (bytes)}\times 8)\times \text{29.99}=5,040,239.36bps=5.04Mbps$

Viewfinder frame 34
#34 (29.99 fps) exp 33216.00 ag 8.00 dg 1.00
FileOutput: output buffer 0x7f9d73a000 size 21008

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3. 部署

3.1 下载

$ git clone https://github.com/SnapDragonfly/libcamera_mon.git

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3.2 编译

$ cd libcamera_mon
$ make
$ tree ./build/
./build/
├── libcamera_mon
├── libcamera_proc.ko
├── libcamera_proc.mod
├── libcamera_proc.mod.c
├── libcamera_proc.mod.o
├── libcamera_proc.o
├── modules.order
└── Module.symvers

1 directory, 8 files

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3.3 安装

$ sudo cp ./build/libcamera_mon /usr/local/bin/fpvdrone/
$ sudo cp ./build/libcamera_proc.ko /usr/local/bin/fpvdrone/
 $ tree /usr/local/bin/fpvdrone/
/usr/local/bin/fpvdrone/
├── font_ardu_hd.png
├── font_ardu.png
├── font_btfl_hd.png
├── font_btfl.png
├── font_inav_hd.png
├── font_inav.png
├── fpv-drone.sh
├── fpv-update.sh
├── libcamera_mon
├── libcamera_proc.ko
└── msposd

1 directory, 11 files

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3.4 配置

$ sudo nano /usr/local/bin/fpvdrone/fpv-drone.sh
$ cat /usr/local/bin/fpvdrone/fpv-drone.sh
#!/bin/bash

# Set up environment variables
export PATH=$PATH:/usr/local/bin:/usr/bin
export LD_LIBRARY_PATH=/usr/local/lib:/usr/lib

# Start the wfb_tx process
/usr/bin/wfb_tx \
  -p 17 \
  -u 14560 \
  -K /etc/drone.key \
  -B 20 \
  -M 1 \
  -S 1 \
  -L 1 \
  -G long \
  -k 1 \
  -n 2 \
  -T 0 \
  -i 7669206 \
  -f data \
  wfb-rf0 &

insmod /usr/local/bin/fpvdrone/libcamera_proc.ko

# Check if /tmp/libcamera/logs FIFO file exists, create it if not
if [ ! -p /tmp/libcamera/logs ]; then
  mkfifo /tmp/libcamera/logs
fi

/usr/local/bin/fpvdrone/libcamera_mon &

# Start libcamera-vid and pipe its output to GStreamer while logging to /tmp/libcamera/logs
/usr/bin/libcamera-vid \
  --verbose \
  --inline \
  --width 1920 \
  --height 1080 \
  --bitrate 4000000 \
  --framerate 30 \
  --hflip \
  --vflip \
  --timeout 0 \
  -o - 2> /tmp/libcamera/logs | \
  /usr/bin/gst-launch-1.0 \
    -v fdsrc ! h264parse ! rtph264pay config-interval=1 pt=35 ! udpsink sync=false host=127.0.0.1 port=5602 &

# Change to the FPVDrone directory and start the msposd process
cd /usr/local/bin/fpvdrone/
/usr/local/bin/fpvdrone/msposd \
  --master /dev/ttyUSB0 \
  --baudrate 115200 \
  --out 127.0.0.1:14560 \
  --matrix 11 \
  --ahi 1 \
  -r 30 \
  -c 7 \
  -c 9 &

# (Optional) Run the FPVDrone update script
# /usr/local/bin/fpvdrone/fpv-update.sh &

# Wait for all background processes to finish
wait

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注：要先加载libcamera_proc.ko，启动libcamera_mon进程，最后打开视频libcamera-vid，上述顺序不能错。

3.5 运行

启动fpv服务以后，使用测试脚本update.sh定时每秒获取当前的fps和bitrate。

$ sudo systemctl start fpvdrone
$ cat update.sh
#!/bin/bash

while true; do
  cat /proc/libcamera_proc
  sleep 1
done
$ ./update.sh
frame=-2, fps=30.00, size=16045, filtered=3.17 Mbps, bitrate=3.85 Mbps
frame=-2, fps=30.01, size=22336, filtered=3.86 Mbps, bitrate=5.36 Mbps
frame=-2, fps=30.01, size=22328, filtered=4.74 Mbps, bitrate=5.36 Mbps
frame=-2, fps=30.01, size=15911, filtered=3.61 Mbps, bitrate=3.82 Mbps
frame=-2, fps=30.00, size=16023, filtered=3.58 Mbps, bitrate=3.85 Mbps
frame=-2, fps=30.01, size=15981, filtered=3.79 Mbps, bitrate=3.84 Mbps
frame=-2, fps=30.01, size=15976, filtered=3.61 Mbps, bitrate=3.83 Mbps
frame=-2, fps=30.01, size=21637, filtered=4.04 Mbps, bitrate=5.19 Mbps
frame=-2, fps=30.01, size=15977, filtered=3.29 Mbps, bitrate=3.84 Mbps
frame=-2, fps=30.01, size=15972, filtered=3.86 Mbps, bitrate=3.83 Mbps
frame=-2, fps=30.01, size=16005, filtered=3.49 Mbps, bitrate=3.84 Mbps
frame=-2, fps=30.01, size=20713, filtered=3.96 Mbps, bitrate=4.97 Mbps
frame=-2, fps=30.01, size=12510, filtered=3.31 Mbps, bitrate=3.00 Mbps
frame=-2, fps=30.01, size=16658, filtered=3.64 Mbps, bitrate=4.00 Mbps
frame=-2, fps=30.00, size=11612, filtered=4.08 Mbps, bitrate=2.79 Mbps

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4. 总结

本文侧重部署libcamera_mon相关的部署，关于服务以及传输层方面的内容，详见：

• msposd 开源代码之树莓派3B+ Bookworm部署
• wfb-ng 开源代码之树莓派3B+ Bookworm无线配置

从数据的角度，可能也可以看出传输速率根据帧数据量的变化，bitrate会不断发生变化，当出现干扰，带宽受限，就会导致丢包率增加，此时很有丢帧情况发生。

在Adpative Link考虑中，更多要从丢包率、信号强度等等参数入手分析，这个，后续会跟进。前期已经简单介绍了一些资料，详见：

【1】OpenIPC开源FPV之Adaptive-Link工程解析
【2】OpenIPC开源FPV之Adaptive-Link天空端代码解析
【3】OpenIPC开源FPV之Adaptive-Link地面站代码解析

接下去，就是在msposd的代码中，类似·sigmastar· 和hisilicon 获取fps和bitrate即可。

5. 后续 - OSD显示FPS/bitrate

目前OpenIPC官网并没有将树莓派作为支持选项，因此提供以下代码和脚本，供需要的朋友使用。

• msposd, support raspberry pi - pr_pi3b_libcamera_vid_mon

$ git clone https://github.com/SnapDragonfly/msposd.git
$ cd msposd
$ git checkout pr_pi3b_libcamera_vid_mon 
$ ./build.sh raspberry
$ sudo cp msposd /usr/local/bin/fpvdrone/msposd

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• libcamera_mon, raspberry pi libcamera-vid monitor tool

$ git clone https://github.com/SnapDragonfly/libcamera_mon.git
$ cd libcamera_mon
$ make
$ sudo cp build/libcamera_mon /usr/local/bin/fpvdrone/libcamera_mon 

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• 打开Option命令行，自定义OSD显示

daniel@raspberrypi:~/msposd $ sudo nano /usr/local/bin/fpvdrone/fpv-drone.sh
daniel@raspberrypi:~/msposd $ cat /usr/local/bin/fpvdrone/fpv-drone.sh
#!/bin/bash

# Set up environment variables
export PATH=$PATH:/usr/local/bin:/usr/bin
export LD_LIBRARY_PATH=/usr/local/lib:/usr/lib

# Start the wfb_tx process
/usr/bin/wfb_tx \
  -p 17 \
  -u 14560 \
  -K /etc/drone.key \
  -B 20 \
  -M 1 \
  -S 1 \
  -L 1 \
  -G long \
  -k 1 \
  -n 2 \
  -T 0 \
  -i 7669206 \
  -f data \
  wfb-rf0 &

insmod /usr/local/bin/fpvdrone/libcamera_proc.ko

# Check if /tmp/libcamera/logs FIFO file exists, create it if not
if [ ! -p /tmp/libcamera/logs ]; then
  mkfifo /tmp/libcamera/logs
fi

/usr/local/bin/fpvdrone/libcamera_mon &

# Start libcamera-vid and pipe its output to GStreamer while logging to /tmp/libcamera/logs
/usr/bin/libcamera-vid \
  --verbose \
  --inline \
  --width 1920 \
  --height 1080 \
  --bitrate 4000000 \
  --framerate 30 \
  --hflip \
  --vflip \
  --timeout 0 \
  -o - 2> /tmp/libcamera/logs | \
  /usr/bin/gst-launch-1.0 \
    -v fdsrc ! h264parse ! rtph264pay config-interval=1 pt=35 ! udpsink sync=false host=127.0.0.1 port=5602 &

# Change to the FPVDrone directory and start the msposd process
cd /usr/local/bin/fpvdrone/
/usr/local/bin/fpvdrone/msposd \
  --master /dev/ttyUSB0 \
  --baudrate 115200 \
  --out 127.0.0.1:14560 \
  --matrix 11 \
  --ahi 1 \
  -r 30 \
  -c 7 \
  -c 9 &

# (Optional) Run the FPVDrone update script
/usr/local/bin/fpvdrone/fpv-update.sh &

# Wait for all background processes to finish
wait

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• change localtime instead of gmtime on OSD display #39

$ cat /usr/local/bin/fpvdrone/fpv-update.sh
#!/bin/bash

ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

while true; do
  echo "Monitor... &L24 &F28 &t CPU:&C &B Temp:&T" > /usr/local/bin/fpvdrone/MSPOSD.msg
  sleep 3
done

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