Cycle-time-measurement-POWERLINK-on-raspberry-pi-2

 

OBJECTIVE

 

To measure performance of the pcap POWERLINK demo while

  • IO data is exchanged in the isochronous phase and
  • A video is streamed over the asynchronous phase
 
The video demonstration shows a master connected with two slaves through a switch. Master runs at 50ms cycle time and transmits payload through Process Data Object (PDO).  
 

DEMO SETUP

 

Figure – 1 Environment Set up

 

PERFORMANCE NUMBERS

 

Configuration

  • Cycle Time: 50 ms
  • Isochronous Data Size: 1 Byte Tx & 1 Byte Rx
  • Asynchronous Data Size: 1500 Bytes
  • The demo C program on the slave receives the data and loops it back into the network
 

Performance

  • The master is able to receive the data is sent into the network after the loop back at a delay of 200ms i.e. 4 cycles.
 

Demo-Powerlink

Figure – 2 Round trip time of a PDO

 
  • During the process master streams a video with the resolution of 176×144 @ 25fps into the network. One of the slaves in the network receives the streamed video with the delay of 2 seconds. The persistence (jitter) between the cycles was measured to be 4ms during the process.
 

img3

Figure – 3 Jitter measurements

 

OBSERVATION

 
  • We see that the network is stable and deterministic at 50 ms
  • To further reduce the cycle time, we can port the ethernet driver into the Linux kernel and try using RtPreempt