BC127 SPP retransmission mode

We are using BC127 to communicate with smart phone using Bluetooth SPP. And we found out that not all data are received. Some data are dropped during the transmission. I think the default L2CAP configuration of BC127 is not set to reliable transmission. Is there any method I can configure the L2CAP parameters of BC127?

Hi @yt.chen

All commands for BC127, it was available in “Melody Audio 7.x User Guide” document, but I cannot find any command in this document to configure the L2CAP parameters.
Let’s feel free to leave question if you have any concern.

Thanks.

I recorded the HCI log of Android device. And found that the configuration of L2CAP of BC127 turned the streaming mode on. Which means the data will not be retransmitted. The application of our product uses BC127 to transmit important data to the smartphones. We need reliable transmission instead of streaming. We also recorded another product using another Bluetooth module witch provides reliable transmission. No data is dropped during the transmission. And I think this is most of SPP application wanted. Can this parameters become configurable?

Hi @yt.chen

Have you tried to use an application on your phone to open SPP profile? It looks like your question is similar with the topic below. Please take a look and share your result.
BC127 - SPP problem

Thanks.

Hi @jerdung ,

Thanks for response. We did set the BC127 to SPP profile and also enter the data mode when transmit the data packets. In Android app, we use the RFCOMM to connect the device. Data can be transmitted to the Android device. But not reliable.

Hi @yt.chen

What does it mean? The phone cannot receive data or a part of the data received on phone was missed?

I tried to send data from the BC127 device to the Phone without any issue.

Thanks

Hi @jerdung ,

Your sample shows that you are using normal command mode to send and receive data. But in our case, we opened the data mode and high speed mode to transmit SPP data. The data flow will be:

DATA => UART => BC127 => Bluetooth SPP Profile => Android

In data mode, data will pass through UART to BC127 to Bluetooth without entering any AT CMD (transparent). And our Bluetooth data drops in high speed transmission. In our case the data rate is 192kbps.

Thanks,
Jackal

Hi @yt.chen ,
Basically, BT is not the best choice to transfer files. I also have ever really reached a high rate when sending files data over the link either with the BC127 or for instance my smartphone to the others a file transfer so I think from the experience it might be more the limitation than the device issue. Sierra developer team was aware of this behavior happens on BC127 v2 and works fine on BC127 v3.
Thanks

Hi @Vianney,

Thanks for the response. We used BC127 Bluetooth SPP to transmit continuous digital data generated from sensors. Data drops is not acceptable in our application. The average data rate we transmit by BC127 SPP is about 200 kbps.

We have tried another product which used another Bluetooth module. They transmit similar data with the slimier data rate using Bluetooth SPP and there is no data dropped. Data will be re-tx and once re-tx counts reach to the max. Connection will lost.

Here is an easy method to reproduce SPP data drops issue:

  1. Continue to transmit data from BC127 to Android device using SPP (Data mode with HIGH SPEED mode)
  2. In Android, enable WiFi hotspot. Use another device to connect hotspot wifi and watch YouTube.
  3. There will be a lot of interference generated from Android phone and you will see that SPP data drops.

I have Android HCI logs (both BC127 and another module). If Sierra Wireless needs the log to analysis. Just contact me by email.

Hi @Vianney ,

We already brought a lot of BC127 v2 in the inventory. We don’t have v3. And there is not way for us to choose v2 or v3 when we buy the modules.

I think the data drop issue is due to the FW instead of the HW. Can this be fixed by FW upgrade? Since we already used a lot of BC 127 v2. We hope the issue can be solved.

Hi @yt.chen

Sierra developer team was aware of this behavior happens on BC127 v2. With latest FW, this issue is not happen on BC127 v3 and there are not plan to fix this issue on BC127 v2.
I think you should be contact to your distributor for supported.

Thanks.

Hi @Vianney ,

Since we may need to use MFi to connect with iOS device. Is BC127 v3 also support MFi? And all the pin mapping is the same as BC127 v2?

Hi @yt.chen

Sierra supports MFI on BC127 following the specific FW named Melody 7.x MFI. you should contact Sierra Wireless Account Manager to obtain this version. So please discuss with your distributor before making any order

I am attaching “BC127 Discovery Board BC127DISKIT001r1.pdf” which describes the necessary information (https://source.sierrawireless.com/resources/airprime/hardware_specs_user_guides/bc127-discovery-kit-manual/#sthash.m1YYlnmg.dpbs).
Please take a look. I cannot find any information relates BC127v2 and v3. So, please confirm with your distributor that the official document is capatible with BC127v3

Thanks.