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Re: [bluetooth-dev] HCI RS-232 SEQ field



Oliver Kasten wrote:

> gordon,
>
>   the rs-232 transport layer is quite similar to the uart transport
> layer. the rs-232 transport layer implements mechanisms to detect errors
> on the serial line. the uart transport layer does not implement these
> mechanisms. quite obviously, implementig the rs-232 layer is more work.
>
> the error detection (recovery?) mechanisms are needed when you are using
> connections with high error rates, e.g. high data rates over long serial
> cables. connections on one-board implementations, where the uart (e.g.
> an rs-232 serial port) of the bt hardware is hardwired to the uart of
> the bt host, are very short and not prone to errors. (i should mention
> that an rs-232 serial port is an instance of class uart!) that's why you
> can do without the error checking mechanisms and therefore make do with
> the uart transport layer.
>
> so how come the rs-232 transport layer isn't used and implemented (it
> isn't, is it?)?
> firstly, the ericsson bt module (roc 101 007, many eval boards, kits,
> etc. are based on that module) only implements the uart and usb
> transport layers. so it wouldn't understand rs-232 packets anyway. and
> secondly, as i understand, the axis folkes are developing the stack to
> use it in their products (one-board implementations!). they simply don't
> need the rs-232 transport layer.
>
> if you run into trouble because of bit errors on the serial line,
> - use a slower bit rate
> - use a shorter serial cable, or
> - implement the rs-232 transport layer (and contribute ;) if you
>   have a bt-hardware that does implement the rs-232 transport layer.
> - use usb instead (you will probably have to upgrade to the latest
>   linux kernel)
>
> hope that helps!
>
> cheers,
> olli*
>
> Gordon McNutt wrote:
> >
> > Browsing the spec again. Noticed that in the HCI RS-232 chapter it
> > claims that HCI packets should prepend both a type and a sequence number
> > field to the HCI packet. HCI UART does not.
> >
> > It appears that the AXIS stack (and the devices we are using it with)
> > use the HCI UART-style packets. But the HCI UART chapter says this is
> > intended for communication between two UARTs on the same PCB. So what's
> > going on? Why aren't all these serial-connected hardware devices
> > expecting RS-232 style packets?
> >
> > --Gordon
> >
> > -
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>
> --
> Oliver Kasten                                phone: +41/ 1/ 63-2 06 63
> ETH-Zurich                                     fax: +41/ 1/ 63-2 16 59
> Haldeneggsteig 4, IFW D48.1                  email: kasten@xxxxxxx.ch
> CH-8092 Zuerich, Switzerland           http://www.inf.ethz.ch/~kasten/

I suspected as much. Thanks for confirming.

--Gordon

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