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Lopez.Antonio
Lopez.Antonio
Associate II
March 22, 2018
Question

community.st.com

  • March 22, 2018
  • 1 reply
  • 1456 views
Posted on March 22, 2018 at 16:00

SPBT3.0DP2 Tx buffering

Hello,

I'm evaluating the SPBT3.0DP2 as a replacement for an AMBER AMB2300 module, which is used in a RS485 to Bluetooth converter device designed around 2007. This converter is used to communicate an Android mobile phone application with an automation controller. The Android application emulates a serial terminal, behaving like an old Televideo 905 device.

So the automation controller is continuosly sending streams of serial data for presenting it on the terminal, i.e. It is continuosly refreshing a display.

The problem I have is that the SPBT3.0DP2 module seems to buffer the data in big chunks before sending it via the BT radio, causing all kinds of display refreshing problems in the Android application, as some effects like blinking are achieved by alternating visualization fields between blank and not blank characters.

This problem doesn't happen when connecting through an AMBER module, as it seems to not buffer so much data before sending it via the BT radio.

My question is, is there a way to reduce the Tx buffering threshold of the SPBT3.0DP2 module? Or do you have any other suggestion to force the module to send the serial data via BT radio at shorter intervals?

Thank you in advance.

Regards.

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1 reply

Lopez.Antonio
Lopez.AntonioAuthor
Associate II
April 3, 2018
Posted on April 03, 2018 at 16:10

Hello,

I'm wondering if somebody from ST technical staff could give an answer to this question. I know this module is in NRND status, but I'm planning on making a last buy if I could manage it to work.

Thank you.

francesco rebucci_O
francesco rebucci_O
Visitor II
April 18, 2018
Posted on April 18, 2018 at 16:35

Hi,

indeed SPBT3.0DP2 module uses big transmit buffers to maximize throughput. If I get correct the application scenario, the solution would be buffering in Android application. You will increase delay, but avoid video refreshing issue.

At SPBT3.0DP2 side one suggestion is to use transmit data chunks of BT SPP packet size (1001 bytes).     

Lopez.Antonio
Lopez.AntonioAuthor
Associate II
April 19, 2018
Posted on April 19, 2018 at 10:40

Thank you for answering, Francesco.

We already tried to implement a delay in the Android application, to mimic the original behaviour of the RS232 connection which had about 1 msec per character refresh rate (at 9600 baud), but unfortunately it didn't solve the problem.

I'm afraid the only solution would be to reduce the transmit buffering level of the SPBT3.0DP2 module.

Do you think it would be possible for ST to provide a new firmware version implementing an AT+AB command for setting the Tx buffering level?

Kind regards.
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