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<== Date ==> <== Thread ==>

Subject: Re: Linux USB serial questions
From: Guy Jennings <jennings@anl.gov>
To: Andrew Johnson <anj@aps.anl.gov>
Cc: tech-talk@aps.anl.gov
Date: Thu, 18 Apr 2013 18:04:11 -0500

On Apr 18, 2013, at 5:12 PM, Andrew Johnson wrote:

Hi Mark,

On 2013-04-18 Mark Rivers wrote:
I don't have a serious need for this device, but there is an EPICS user at NIH, Andrew Gomella who needs to control 18 of the model 3006 devices,
which he is planning to do from a single Linux box.

Is this possible, even in kernel 3.8?

It should be possible even with your kernel version. The issue that Guy described is that the driver can only talk to one *type* of device at once; so as long as all 18 are the same model 3006 with the same product ID he should
be fine.

Not quite what I meant - the ftdi_sio module can handle a mixture of devices from those device types it has compiled in, and ONE additional vendor:product
combination passed as an option.


The other question is whether it provides a serial number attribute that can be used in a udev configuration file to ensure that the /dev/ttyUSB* nodes always map to the same physical devices. If there is no such attribute then unplugging 2 devices and plugging them back in could cause the mapping to change, which could be disastrous. Of course managing all 18 units and
replacing them with spares still becomes a rather complicated chore.

If it doesn't provide a serial number he's in big trouble! I think that the order in which USB ports are scanned is deterministic, so as long as he doesn't unplug or replug a device the mapping might stay constant - but I wouldn't like to rely
on it!

Guy


- Andrew
--
It is difficult to get a man to understand something, when his salary
depends upon his not understanding it. -- Upton Sinclair


References:
Linux USB serial questions Mark Rivers
Re: Linux USB serial questions J. Lewis Muir
RE: Linux USB serial questions Mark Rivers
Re: Linux USB serial questions Andrew Johnson

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