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



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
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