Last year I looked at the source for Apple's CDC-ACM drivers, from 10.6 to 10.9.The diff from 10.9 to Yosemite shows that the memory allocation method for ring buffers changed. I do not know why the new method would cause the effects you see, and it might be something higher up in the USB driver. While it is tricky with permissions and codesigned kexts, you could try using the /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBCDCACMData.kext /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBCDCACMControl.kext
from 10.9 in 10.10 and see if the results are the same. ---------------------------------------------------------------------- Message: 1 Date: Wed, 18 Mar 2015 12:40:32 +0200 From: Kustaa Nyholm <[email protected]> To: [email protected] Subject: Yosemite USB CDC ACM Message-ID: <[email protected]> Content-Type: text/plain; charset="iso-8859-1"; Format="flowed" On a fresh install of Yosemite my USB CDC ACM device fails badly. Now the fact that it won't re-appear after re-plugging, suggest something is wrong on the device side firmware. With every other (than Yosemite) operating system I've tested the system the OS has no problem enumerating the device after a re-plug. However the primary problem is that something goes south during normal communication and this I'm not convinced is a device side issue. Of course it can be a device side firmware issue, not denying that. The USB CDC ACM 'stack' on the device is a bare minimum supporting only the absolutely mandatory features as per the USB spec. Googling around I see that several virtual devices both custom driver based (FTDI) and Apple driver based (ie real USB CDC ACM devices) have experienced problems with Yosemite. Now I'm looking for ideas on how to debug this further and also fishing for info on what has changed on Yosemite and hunches about what could be the problem. br Kusti
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