How to carry OM-D E-M5 to be accessible when backpacking?

I'm thinking about getting an OM-D E-M5 for backpacking and I'm wondering what the options are for carrying it in a way that it is easily accessible while backpacking without removing the pack, that would be handsfree carry (both hands will be on trekking poles) and would provide some security/protection so that the camera isn't going to swing around and bump into things.  It also needs to not interfere or complicate taking the backpack on/off.

Any ideas for how to best carry it?

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John
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