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Strange failure mode on MacBook Pro Bluetooth. 50ms delays between writes.
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Strange failure mode on MacBook Pro Bluetooth. 50ms delays between writes.


  • Subject: Strange failure mode on MacBook Pro Bluetooth. 50ms delays between writes.
  • From: Donald Ness <email@hidden>
  • Date: Fri, 03 Jul 2015 11:20:39 -0600

I’m developing a Bluetooth application on a Late 2012 MacBook Pro running Yosemite 10.10.4 and I’m experiencing a strange issue where there are ~50ms delays between every 100 bytes or so sent from the Mac to the Bluetooth device. Here is a screenshot from the logic analyzer attached to the Bluetooth device’s RX pin that shows the behavior:

https://cloud.githubusercontent.com/assets/622192/8443465/2b8cf544-1f44-11e5-9301-65af70fbdadd.png

The embedded platform I’m using is an AVR micro with an AmpedRF Bluetooth radio. For the test, I wrote a very simple program for the micro that just reads the bytes from the USART as fast as possible and discards them.

The device is not asserting its RTS pin, so flow control does not appear to be the issue.

In fact, I’ve run this exact same test on another Late 2012 MacBook Pro also running Yosemite, and did not experience the issue. The bytes come in continuously, with no delays:

https://cloud.githubusercontent.com/assets/622192/8443423/d8c97274-1f43-11e5-9a0a-f2ff205de71a.png

This makes me think that either I have some misconfigured Bluetooth settings on my Mac, or my Mac’s Bluetooth hardware is exhibiting a strange failure mode. I’ve tried wiping my /Library/Preferences/com.apple.Bluetooth.plist as well as all my /Library/Preferences/SystemConfiguration/*.plist to no avail.

What other settings could I check? Could this be a hardware failure?

Thanks,

Donald
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