We're loosing serial bytes from PC to phone

Harald Welte laforge at gnumonks.org
Sun Mar 21 09:35:10 UTC 2010


Hi!

It seems we're loosing serial characters on their way from the (Linux)
PC to the phone.

I think I've seen this at some point in the past, but now I'm seeing it
constantly.

Let's assume we're trying to send the following sequence of bytes from
the PC side to the phone in one of the HLDC connections:
> send_to_phone(dlci=5): 0a 00 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d
> 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25
> 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 

what we actually get from the sercomm callback on the phone is:

> l1a_l23_rx_cb: 0a 00 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12
> 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 27 28 29 2a
> 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 

as you can see, there is a '00 01' missing between the '00' and the '02'.

Interestingly, putting a usleep(10000) after every serial write does not
solve the problem, so it is not timing related.  We don't get any UART
overflows on the calypso, either.

If I change the data pattern, then the first bytes are transmitted fine,
but as soon as there is one 00 bytes, two characters are missing from
the stream.

If I strace osmocon, it is clear that we write every character,
including the null-bytes, and all of the writes are successfully.

I've again looked at (and played with) the termios settings, but could
not find any problem (nor solution).

It's also not the sercomm layer that is loosing bytes, as I the
characters appear already lost when printing them from within the
calypso UART driver, as you can see here:

getchar_nb(1) = 7e	// flag character
getchar_nb(1) = 05	// hdlc
getchar_nb(1) = 03	// hdlc
getchar_nb(1) = 0a	// l1ctl_hdr (undefined msg_type 10)
getchar_nb(1) = 00	// padding
getchar_nb(1) = 02	// here should be 00, 01, 02...
getchar_nb(1) = 03
getchar_nb(1) = 04
getchar_nb(1) = 05
[...]

Any ideas? It's really strange and I don't really know what else to do.
I'm quite sure our binaries contain multiple successive null-bytes and
their download is working great...

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)




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