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Author Topic: CDC ACM Setting without Getting Line Coding and State  (Read 11310 times)

remixed123

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CDC ACM Setting without Getting Line Coding and State
« on: October 08, 2013, 10:55:05 am »
I am working with an embedded USB host that connects with only a few different USB devices.

These devices are all CDC ACM devices and I know all the settings they require for communication.

Hence, I was wondering can I skip the process of Getting Line Coding and Line State details from the device.
And just directly set the Line Coding and Line State as I know they will require?

Are there any issues to consider with this approach?

Glenn.
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Jan Axelson

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Re: CDC ACM Setting without Getting Line Coding and State
« Reply #1 on: October 08, 2013, 02:34:27 pm »
I don't see any issues with just setting the states.
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Bret

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Re: CDC ACM Setting without Getting Line Coding and State
« Reply #2 on: October 08, 2013, 06:35:03 pm »
There shouldn't be a problem with just setting the states, but some devices expect things to happen in a specific order/pattern and don't work correctly otherwise (Mass Storage Devices e.g. can be especially bad about that).  If it doesn't work, you may need to go back and download the "unnecessary" data just to keep the device happy.
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Barry Twycross

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Re: CDC ACM Setting without Getting Line Coding and State
« Reply #3 on: October 08, 2013, 07:20:34 pm »
My CDC devices just ignores those requests, they're more of an annoyance to me. Unless there's a uart somewhere, they really don't mean anything.

Bret's answer is the right one, you don't need to, unless the device gets upset by that.
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