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ANT Latency

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Joined 2014-02-03

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Dear All
I'm currently evaluating ANT protocol to transmit/receive MIDI.
My main concern is latency issue, I plan to use a CC2571 8 channels ANT transceiver, and was wondering if that ANT protocol could be use to transmit and receive data with low latencies (about 10ms or lower).

From what I've found in the data sheets, it seems the channels period could be as low as 5ms, does it mean a single transceiver could be polled by the master each 5ms ?

Anyone here experienced MIDI over ANT ?
Thanks for any tip or suggestion
Jerome      
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Total Posts: 235

Joined 2012-08-31

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Hi Jerome,

This is an interesting application for ANT, and I am not aware of anyone who has used ANT for MIDI so far. I do know of an application running at ~200Hz in commercial product, but this is not a common usage.

My guess is, that you may be able to get it to work, but it's near the limit of ANT bandwidth so you may need to tweak your setup to make it reliable. Make sure you have a high baud rate and can handle the data throughput to and from ANT.

I ran a quick test using a USB-m connected to ANTwareII and opened 3 channels at 200Hz. The first channel operated fine when it was the only one open. When I opened the second channel, both channels were mostly fine, except for a channel collision appearing every ~5 seconds or so. I then tried to open the 3rd channel and it wouldn't open. I didn't change any of the channel defaults other than the channel period.

I can get 2 channels running at 100Hz that don't appear to be colliding. Adding a third causes lots of collisions - the three channels aren't really working at this point.

It seems to work better if I open the channels at 4Hz, then increase the channel period to 100Hz or 200Hz - otherwise it seems that the second channel has difficulty finding a clear slot to transmit in and takes a long time to open.

The USB-m datasheet specifies a combined message rate up to 190Hz which seems consistent with this result, although I've pushed it a bit further than the part is designed for.

This assumes 8 byte payload, and my test used broadcast messages. If you will be using burst messages, you may run into problems sooner. You could also consider a lower channel period combined with burst messages. Advanced burst allows up to 60kbps.

So it depends how many devices you need to connect and how much data you need to send on each channel period.

I'm also curious about your topology - polling each transceiver by a master can be achieved using an ANT shared channel. More commonly in the ANT world the device that has most data to send is defined as the master and just transmits data every channel period. The receiving device(s) can then synchronize with the master's transmissions and do not need to poll it.

If you are not familiar with this already then the video on this page does a good job of illustrating the concept: http://www.thisisant.com/developer/

In addition you will need to read the ANT message protocol and usage document: http://www.thisisant.com/developer/

Good luck!