Reducing Latency in UDP Communications

8 次查看（过去 30 天）
Michael
Michael 2015-8-13
编辑： Uladzimir 2015-8-18
I am working on a project where we are flying a quadcopter with an onboard Raspberry Pi which communicates with a host PC. I am currently developing the communications between the two systems using UDP protocols. I am using two Simulink models, one on the PC and one built onto the Pi, that both use the Raspberry Pi UDP Send and Receive blocks. There is very little else in the models - just a clock to generate a signal to send back and forth, and byte pack and unpack blocks. While I have been able to successfully send information back and forth, the latency has been extremely high, ranging anywhere from 2-7 seconds. Obviously, this is not practical for real-time applications. This latency is approximately the same, independent of whether both computers are communicating over WiFi or connected to a router via Ethernet. In addition, ping times between the two systems are low (<5 ms), so I don't believe the hardware configuration to be a problem.
Would anyone be able to provide a few tips or pointers towards helping to reduce the messaging latency?
Thanks.
  2 个评论
Walter Roberson
Walter Roberson 2015-8-13
Is the packet size variable? Did you specify the exact number of values expected for the packet?
If you were using the MATLAB routines directly I would have you check your DatagramTerminateMode
Unfortunately I am having difficulty finding specific documentation on the Raspberry Pi UDP Receive block; I see it exists but the documentation basically says "Open the library and take a look"
Michael
Michael 2015-8-14
The package size is fixed. As of right now, I am just sending one double value back and forth. Both receive blocks are expecting a packet of that size, and receive it correctly, just with high latency.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Uladzimir
Uladzimir 2015-8-14
Dear Michael, You should run your models in external mode. According to mathworks manual for real-time windows target, it provides efficiency up to 20 kHz. For this you need to set discrete fixed step solver, set up rtwin.tlc file in code generation options, then build model and run it in external mode. You could use Packet Input and Packet Output blocks, tuned as standard udp device. Our model worked with 1..3 ms delay.
  5 个评论
显示 3更早的评论
Uladzimir
Uladzimir 2015-8-18
I got your point. There is a lot to think about. What solver do you use? I used discrete, fixed-step. Also, you could try real-tyme sync block, it shows amount of missed ticks.
Uladzimir
Uladzimir 2015-8-18
编辑：Uladzimir 2015-8-18
P.S. I've just looked through my normal-mode model and noticed that here UDP SEND Binary and Receive Binary blocks were used. It have a size of the packet option. Also I remember, that there were troubles with byte alignment on the embedded side.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Run on Target Hardware 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by