Cortex M7 vs. Parrot Bebop 2.

It is interesting to note that the CPU load running flight control on the STM32F7 on a single core is comparable to the CPU load  on a much faster single core of a Parrot Bebop 2:

Below is the load on Bebop (percentage in the list is a single core)

Mem: 66516K used, 230236K free, 0K shrd, 15268K buff, 22992K cached
CPU: 10.3% usr 21.7% sys 0.0% nic 67.4% idle 0.0% io 0.0% irq 0.5% sirq
Load average: 1.53 0.80 0.32 3/113 1221
 PID PPID USER STAT VSZ %VSZ CPU %CPU COMMAND
 1200 1187 root S 36468 12.2 0 26.1 px4 /home/root/ /home/root/px4.config

And here is the load on a Cortex M7 (STM32F7, complete system load)

Processes: 21 total, 4 running, 17 sleeping
CPU usage: 31.33% tasks, 1.39% sched, 67.28% idle
DMA Memory: 5120 total, 1536 used 1536 peak
Uptime: 91.005s total, 61.744s idle

The similar number despite of the advantage of the Parrot Bebop 2 in clock speed makes sense: Flight control consists of many short interleaving tasks and sensor driver access for which Linux is not designed specifically, while the NuttX RTOS is. It also sheds a light on why prosumer drone manufacturers like DJI and Yuneec as well as Intel have retained an independent microcontroller for flight control in their models. Qualcomm is offering a smart hybrid approach by running PX4 on the DSP of the Snapdragon SoC, leaving Linux to run computer vision.

 

© PX4 Dev Team