Number of Slaves supported in BTLE and ANT?

John,

I am not sure about the exact numbers. I'll check with some members on the team. We work on CC256x/CC2570 products.

For ANT, some information about the possible topology is here:

http://www.thisisant.com/technology/feature-highlights

"For a given star network, if each link needs an independent ANT channel, the maximum number of devices is the channel capability of the ANT device used by the hub, which can be 8 if using AP2 or AT3 products."

I believe that we should at least match with the CC2570 AP2 or AT3 and I don't believe your throughput requirements are a problem.

Gustavo

Some additional research into BTLE yielded the following:

"A master Bluetooth device can communicate with up to seven devices in a piconet. (An ad-hoc computer network using Bluetooth technology) The devices can switch roles, by agreement, and the slave can become the master at any time."

So it looks like BTLE and ANT are more or less identical in terms of # of devices and range.

Hi John,

Just to comment some on BLE v ANT.    For BLE you can have a huge number of slaves supported >200. This is limited by connection interval, data throughput, and implementation of the master.  In the case of CC2540, out master will support up to 4 slaves. This is mainly an memory issue, as the CC2540 is really designed to be the sensor with low MCU and power requirements.  BLE in devices such as phones and computers will likely support many simultaneous slave connections.  In our current stack implementation for CC2540, the device will have to stay either slave or master as these are different libraries.

For ANT the 2571 has 8 nodes which can be either master or slave, these can be configured. The 2570 will only have one node which can be switched between master and slave.   BLE only supports star network, whereas the ANT solution supports star as well many other topologies. 

Another big diff is that CC2540 is SOC, and CC257x requires an external MCU to control it.

-Greg

Thanks for the clarification.  It's easy to get lost in this stuff.

Just to chime in on the ANT side of things here, ANT sends 8 byte packets (data payload), and has a max of 8 simultaneous channels / connections per device (when using the 8 channel variant). I imagine just like BLE, these channels share the same physical radio, so the more active channels you add, the less bandwidth each channel has to operate with. As a rough guide, we say that an ANT device running a single channel can do about 200 Hz max. With 8 channels running, each channel could probably do 8 Hz (meeting the original requirement of 4 bytes at 16 Hz with 8 slaves). However, when you get into high data rates like this, other factors tend to come into play that limit the speed - namely mcu and serial port speed.

Hi, 

sorry for cross posting in an old thread, but we are facing some problems with the TI USB dongle (CC2540F256) using more than 3 slaves and we aren't able to understand what is causing these packet loss problems. Now in your post I read that the CC2540 master is able to support only up to four slaves... I'd like, if possible, to know more about this restriction and what are the memory limitations that are forcing the limit of 4 slave nodes.

Thank you.

Best regards,

Samuele Forconi.

Does the new CC2540 stack available for download? (the one predicted to be available this summer)

Because the old one permits only 1 estabilished connection in the same moment, the 4 was a feature for this new version ...

Or You are using only 1 estabilished connection, using the slaves one by one?

br,

Brown

Hi Brown,

thanks for your reply.

We currently have 4 slave nodes in advertising for 100ms once per second.

What's happening is that with 4 slave nodes the master hangs and receives the advertising data only of three of them simultaneously. 

I tested this behaviour using B-Tool, with 4 slaves and 1 master (TI USB dongle) - each time I perform a Device Dicovery B-Tool reports only 3 device found. 

With only 2 or 3 devices this problem is not present, B-Tool discovers the right number of devices.

I can't understand what's happening.

Thanks.

Regards,
Samuele Forconi. 

Hm - are you sure not BTool sets this way?

I just checked BTool and the first message looks like this:

[1] : <Tx> - 01:00:45.408

-Type : 0x01 (Command)

-Opcode : 0xFE00 (GAP_DeviceInit)

-Data Length : 0x26 byte(s)

 ProfileRole : 0x08 (Central)

 MaxScanRsps : 0x03

 IRK : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 

 CSRK : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 

 SignCounter : 0x00000001

Just found it - go in BTool to the Adv. commands tab

Search for Gap/Gap_DeviceInit

Modify maxscanrsps to 4 (or bigger)

Rightclick on Gap_DeviceInit and Send

And see what happens.

B.

You're right,

that was the issue. 

Now I'm able to see all my devices working!

Thank you very much!

Regards,

Samuele.

Hello,

I'm interested in your conversation, because I want to design a star network based on BLE technology, so my question is : what is the actual limit of slaves that we can associate in a BLE star network ? I read in the document "Texas Instruments CC2540/41 Bluetooth® Low Energy Software Developer’s Guide v1.2" that the maximum is 3, and I find here that we can associate more than 3 !? 

Mehdi