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Re: [lwip-users] lwip-users Digest, Vol 214, Issue 6

From: Bas Prins
Subject: Re: [lwip-users] lwip-users Digest, Vol 214, Issue 6
Date: Mon, 7 Jun 2021 22:43:06 +0200
Dear Rüdiger ,

Thanks for the detailed answer and the link (haven't read that, learned a lot from reading).

When I read this, I understand what you mentioned, and that the sender is allowed to omit the TRAILING 0x7e byte. But in my case, it's not really the trailing byte (or I am still missing the obvious here... :))

It might be hard to digest from the CSV data, but this is what I can see in my logic analyzer:

STM starts (after modem reaches data mode): 
0x7e ..... 0x7e - send first packet, wrapped in 0x7e bytes.

After roughly 500us the peer replies: 
0x7e ...... 0x7e - again a ppp packet wrapped in 0x7e bytes

STM responds and sends a second packet: 
0xFF .. 0x7e : This is what struck me. Shouldn't this BEGIN with a 0x7e?

It already sent it's "omitable leading 0x7e byte" to enclose the first packet. So it should start with a 0x7e byte now, right? Or does the peer accept the trailing 0x7e byte of the FIRST sent packet as leading 0x7e for the second packet??

I interpreted this part as the FIRST 0x7e byte of the second sent PPP packet is omitted. 

What am I still missing?

Best regards, bas





Op ma 7 jun. 2021 om 21:28 schreef <lwip-users-request@nongnu.org>:
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Today's Topics:

   1. Re: pppos sent packets optionally start with 0x7e, why?
      (Rüdiger Asche)


----------------------------------------------------------------------

Message: 1
Date: Mon, 7 Jun 2021 21:27:33 +0200
From: Rüdiger Asche <ruediger_asche@t-online.de>
To: "Mailing list for lwIP users" <lwip-users@nongnu.org>
Subject: Re: [lwip-users] pppos sent packets optionally start with
        0x7e, why?
Message-ID: <F01ACCC173FC4DFB8EC67D8A6C1E9859@RACTOMCOVE>
Content-Type: text/plain; charset="utf-8"

Hi there Bas,

have you looked at the HDLC encoding rules? In https://en.wikipedia.org/wiki/Point-to-Point_Protocol , about half way down, it reads

"0x7E, omitted for successive PPP packets"

for the frame END character. So to me it looks as if it's not the leading frame character but the trailing one that's missing, which is specification compliant. Makes sense too to omit it because the inner structure of a frame past the sync char allows for full parsing of a well formed packet (of course taking into account the negotiated PFC and AFC compression restrictions). Note that the first LCP packet (decoded here) is still fully framed:

ff03 c021 1 1                      => LCP conf request
              0 14                 => length
                   2 6 0 0 0 0     =>
                   5 6 40 b1 9c e9 => magic number
                   7 2             => Protocol field compression
                   8 2             => AFC compression
38 b7           =>                 => frame checksum


Afterwards, both sides have all the information they need to parse a peer's frame without a trailing framing character.



  ----- Original Message -----
  From: Bas Prins
  To: lwip-users@nongnu.org
  Sent: Monday, June 07, 2021 7:00 PM
  Subject: Re: [lwip-users] pppos sent packets optionally start with 0x7e, why?


  I think the CSV attachment was dropped by server. Trying to add the CSV as plain text below.


  Async Serial == RX
  Async Serial [1] == TX


  Leading 0x7E byte is not provided by LWIP in when it calls sio_write.






        name type start_time duration data

        Async Serial [1] data 5.80629 8.25E-05 0x41

        Async Serial [1] data 5.806378 8.25E-05 0x54

        Async Serial [1] data 5.806466 8.25E-05 0x0D

        Async Serial [1] data 6.936377 8.25E-05 0x2B

        Async Serial [1] data 6.946236 8.25E-05 0x2B

        Async Serial [1] data 6.95636 8.25E-05 0x2B

        Async Serial data 7.865252 8.25E-05 0x0D

        Async Serial data 7.865339 8.25E-05 0x0A

        Async Serial data 7.865426 8.25E-05 0x4F

        Async Serial data 7.865513 8.25E-05 0x4B

        Async Serial data 7.865599 8.25E-05 0x0D

        Async Serial data 7.865686 8.25E-05 0x0A

        Async Serial [1] data 7.869666 8.25E-05 0x41

        Async Serial [1] data 7.869754 8.25E-05 0x54

        Async Serial [1] data 7.869842 8.25E-05 0x4F

        Async Serial [1] data 7.86993 8.25E-05 0x0D

        Async Serial data 7.871056 8.25E-05 0x0D

        Async Serial data 7.871143 8.25E-05 0x0A

        Async Serial data 7.87123 8.25E-05 0x43

        Async Serial data 7.871317 8.25E-05 0x4F

        Async Serial data 7.871403 8.25E-05 0x4E

        Async Serial data 7.87149 8.25E-05 0x4E

        Async Serial data 7.871577 8.25E-05 0x45

        Async Serial data 7.871664 8.25E-05 0x43

        Async Serial data 7.871751 8.25E-05 0x54

        Async Serial data 7.871837 8.25E-05 0x20

        Async Serial data 7.871924 8.25E-05 0x31

        Async Serial data 7.872011 8.25E-05 0x31

        Async Serial data 7.872098 8.25E-05 0x35

        Async Serial data 7.872185 8.25E-05 0x32

        Async Serial data 7.872271 8.25E-05 0x30

        Async Serial data 7.872358 8.25E-05 0x30

        Async Serial data 7.872445 8.25E-05 0x0D

        Async Serial data 7.872532 8.25E-05 0x0A up until here is AT commands to put modem in ppp. That succeeded here.
        Async Serial [1] data 7.895673 8.25E-05 0x7E First packet sent over uart from STM
        Async Serial [1] data 7.895761 8.25E-05 0xFF

        Async Serial [1] data 7.895849 8.25E-05 0x7D

        Async Serial [1] data 7.895937 8.25E-05 0x23

        Async Serial [1] data 7.896025 8.25E-05 0xC0

        Async Serial [1] data 7.896113 8.25E-05 0x21

        Async Serial [1] data 7.896201 8.25E-05 0x7D

        Async Serial [1] data 7.896289 8.25E-05 0x21

        Async Serial [1] data 7.896377 8.25E-05 0x7D

        Async Serial [1] data 7.896465 8.25E-05 0x21

        Async Serial [1] data 7.896553 8.25E-05 0x7D

        Async Serial [1] data 7.896641 8.25E-05 0x20

        Async Serial [1] data 7.896729 8.25E-05 0x7D

        Async Serial [1] data 7.896817 8.25E-05 0x34

        Async Serial [1] data 7.896905 8.25E-05 0x7D

        Async Serial [1] data 7.896993 8.25E-05 0x22

        Async Serial [1] data 7.897081 8.25E-05 0x7D

        Async Serial [1] data 7.897169 8.25E-05 0x26

        Async Serial [1] data 7.897257 8.25E-05 0x7D

        Async Serial [1] data 7.897345 8.25E-05 0x20

        Async Serial [1] data 7.897433 8.25E-05 0x7D

        Async Serial [1] data 7.897521 8.25E-05 0x20

        Async Serial [1] data 7.897609 8.25E-05 0x7D

        Async Serial [1] data 7.897697 8.25E-05 0x20

        Async Serial [1] data 7.897785 8.25E-05 0x7D

        Async Serial [1] data 7.897872 8.25E-05 0x20

        Async Serial [1] data 7.89796 8.25E-05 0x7D

        Async Serial [1] data 7.898048 8.25E-05 0x25

        Async Serial [1] data 7.898136 8.25E-05 0x7D

        Async Serial [1] data 7.898224 8.25E-05 0x26

        Async Serial [1] data 7.898312 8.25E-05 0x40

        Async Serial [1] data 7.8984 8.25E-05 0xB1

        Async Serial [1] data 7.898488 8.25E-05 0x9C

        Async Serial [1] data 7.898576 8.25E-05 0xE9

        Async Serial [1] data 7.898664 8.25E-05 0x7D

        Async Serial [1] data 7.898752 8.25E-05 0x27

        Async Serial [1] data 7.89884 8.25E-05 0x7D

        Async Serial [1] data 7.898928 8.25E-05 0x22

        Async Serial [1] data 7.899017 8.25E-05 0x7D

        Async Serial [1] data 7.899105 8.25E-05 0x28

        Async Serial [1] data 7.899193 8.25E-05 0x7D

        Async Serial [1] data 7.899281 8.25E-05 0x22

        Async Serial [1] data 7.899369 8.25E-05 0x38

        Async Serial [1] data 7.899457 8.25E-05 0xB7

        Async Serial [1] data 7.899545 8.25E-05 0x7E end first packet
        Async Serial data 7.900403 8.25E-05 0x7E first received ppp packet on rx line
        Async Serial data 7.90049 8.25E-05 0xFF

        Async Serial data 7.900576 8.25E-05 0x7D

        Async Serial data 7.900663 8.25E-05 0x23

        Async Serial data 7.90075 8.25E-05 0xC0

        Async Serial data 7.900837 8.25E-05 0x21

        Async Serial data 7.900924 8.25E-05 0x7D

        Async Serial data 7.90101 8.25E-05 0x21

        Async Serial data 7.901097 8.25E-05 0xE5

        Async Serial data 7.901184 8.25E-05 0x7D

        Async Serial data 7.901271 8.25E-05 0x20

        Async Serial data 7.901358 8.25E-05 0x7D

        Async Serial data 7.901444 8.25E-05 0x39

        Async Serial data 7.901531 8.25E-05 0x7D

        Async Serial data 7.901618 8.25E-05 0x22

        Async Serial data 7.901705 8.25E-05 0x7D

        Async Serial data 7.901792 8.25E-05 0x26

        Async Serial data 7.901878 8.25E-05 0x7D

        Async Serial data 7.901965 8.25E-05 0x20

        Async Serial data 7.902052 8.25E-05 0x7D

        Async Serial data 7.902139 8.25E-05 0x20

        Async Serial data 7.902226 8.25E-05 0x7D

        Async Serial data 7.902312 8.25E-05 0x20

        Async Serial data 7.902399 8.25E-05 0x7D

        Async Serial data 7.902486 8.25E-05 0x20

        Async Serial data 7.902573 8.25E-05 0x7D

        Async Serial data 7.90266 8.25E-05 0x23

        Async Serial data 7.902746 8.25E-05 0x7D

        Async Serial data 7.902833 8.25E-05 0x25

        Async Serial data 7.90292 8.25E-05 0xC2

        Async Serial data 7.903007 8.25E-05 0x23

        Async Serial data 7.903094 8.25E-05 0x7D

        Async Serial data 7.90318 8.25E-05 0x25

        Async Serial data 7.903267 8.25E-05 0x7D

        Async Serial data 7.903354 8.25E-05 0x25

        Async Serial data 7.903441 8.25E-05 0x7D

        Async Serial data 7.903528 8.25E-05 0x26

        Async Serial data 7.903614 8.25E-05 0x26

        Async Serial data 7.903701 8.25E-05 0xA6

        Async Serial data 7.903788 8.25E-05 0x32

        Async Serial data 7.903875 8.25E-05 0x2F

        Async Serial data 7.903962 8.25E-05 0x7D

        Async Serial data 7.904049 8.25E-05 0x27

        Async Serial data 7.904135 8.25E-05 0x7D

        Async Serial data 7.904222 8.25E-05 0x22

        Async Serial data 7.904309 8.25E-05 0x7D

        Async Serial data 7.904396 8.25E-05 0x28

        Async Serial data 7.904483 8.25E-05 0x7D

        Async Serial data 7.904569 8.25E-05 0x22

        Async Serial data 7.904656 8.25E-05 0xD7

        Async Serial data 7.904743 8.25E-05 0x73

        Async Serial data 7.90483 8.25E-05 0x7E

        Async Serial data 7.904917 8.25E-05 0x7E

        Async Serial data 7.905003 8.25E-05 0xFF

        Async Serial data 7.90509 8.25E-05 0x7D

        Async Serial data 7.905177 8.25E-05 0x23

        Async Serial data 7.905264 8.25E-05 0xC0

        Async Serial data 7.905351 8.25E-05 0x21

        Async Serial data 7.905437 8.25E-05 0x7D

        Async Serial data 7.905524 8.25E-05 0x22

        Async Serial data 7.905611 8.25E-05 0x7D

        Async Serial data 7.905698 8.25E-05 0x21

        Async Serial data 7.905785 8.25E-05 0x7D

        Async Serial data 7.905871 8.25E-05 0x20

        Async Serial data 7.905958 8.25E-05 0x7D

        Async Serial data 7.906045 8.25E-05 0x34

        Async Serial data 7.906132 8.25E-05 0x7D

        Async Serial data 7.906219 8.25E-05 0x22

        Async Serial data 7.906305 8.25E-05 0x7D

        Async Serial data 7.906392 8.25E-05 0x26

        Async Serial data 7.906479 8.25E-05 0x7D

        Async Serial data 7.906566 8.25E-05 0x20

        Async Serial data 7.906653 8.25E-05 0x7D

        Async Serial data 7.906739 8.25E-05 0x20

        Async Serial data 7.906826 8.25E-05 0x7D

        Async Serial data 7.906913 8.25E-05 0x20

        Async Serial data 7.907 8.25E-05 0x7D

        Async Serial data 7.907087 8.25E-05 0x20

        Async Serial data 7.907173 8.25E-05 0x7D

        Async Serial data 7.90726 8.25E-05 0x25

        Async Serial data 7.907347 8.25E-05 0x7D

        Async Serial data 7.907434 8.25E-05 0x26

        Async Serial data 7.907521 8.25E-05 0x40

        Async Serial data 7.907608 8.25E-05 0xB1

        Async Serial data 7.907694 8.25E-05 0x9C

        Async Serial data 7.907781 8.25E-05 0xE9

        Async Serial data 7.907868 8.25E-05 0x7D

        Async Serial data 7.907955 8.25E-05 0x27

        Async Serial data 7.908042 8.25E-05 0x7D

        Async Serial data 7.908128 8.25E-05 0x22

        Async Serial data 7.908215 8.25E-05 0x7D

        Async Serial data 7.908302 8.25E-05 0x28

        Async Serial data 7.908389 8.25E-05 0x7D

        Async Serial data 7.908476 8.25E-05 0x22

        Async Serial data 7.908562 8.25E-05 0xD3

        Async Serial data 7.908649 8.25E-05 0xDE

        Async Serial data 7.908736 8.25E-05 0x7E end first received ppp packet
        Async Serial [1] data 7.913322 8.25E-05 0xFF second ppp packet sent by STM, why is the 0x7E byte ommitted? I also attached debugger to get data bytes provided by LWIP, first byte is -0xFF
        Async Serial [1] data 7.91341 8.25E-05 0x7D

        Async Serial [1] data 7.913498 8.25E-05 0x23

        Async Serial [1] data 7.913586 8.25E-05 0xC0

        Async Serial [1] data 7.913674 8.25E-05 0x21

        Async Serial [1] data 7.913762 8.25E-05 0x7D

        Async Serial [1] data 7.91385 8.25E-05 0x24

        Async Serial [1] data 7.913938 8.25E-05 0xE5

        Async Serial [1] data 7.914026 8.25E-05 0x7D

        Async Serial [1] data 7.914114 8.25E-05 0x20

        Async Serial [1] data 7.914202 8.25E-05 0x7D

        Async Serial [1] data 7.91429 8.25E-05 0x29

        Async Serial [1] data 7.914378 8.25E-05 0x7D

        Async Serial [1] data 7.914466 8.25E-05 0x23

        Async Serial [1] data 7.914554 8.25E-05 0x7D

        Async Serial [1] data 7.914642 8.25E-05 0x25

        Async Serial [1] data 7.91473 8.25E-05 0xC2

        Async Serial [1] data 7.914818 8.25E-05 0x23

        Async Serial [1] data 7.914906 8.25E-05 0x7D

        Async Serial [1] data 7.914994 8.25E-05 0x25

        Async Serial [1] data 7.915082 8.25E-05 0x7A

        Async Serial [1] data 7.91517 8.25E-05 0xEF

        Async Serial [1] data 7.915258 8.25E-05 0x7E

        Async Serial data 7.915929 8.25E-05 0x7E

        Async Serial data 7.916016 8.25E-05 0xFF

        Async Serial data 7.916102 8.25E-05 0x7D

        Async Serial data 7.916189 8.25E-05 0x23

        Async Serial data 7.916276 8.25E-05 0xC0

        Async Serial data 7.916363 8.25E-05 0x21

        Async Serial data 7.91645 8.25E-05 0x7D

        Async Serial data 7.916536 8.25E-05 0x21

        Async Serial data 7.916623 8.25E-05 0xE6

        Async Serial data 7.91671 8.25E-05 0x7D

        Async Serial data 7.916797 8.25E-05 0x20

        Async Serial data 7.916884 8.25E-05 0x7D

        Async Serial data 7.916971 8.25E-05 0x34

        Async Serial data 7.917057 8.25E-05 0x7D

        Async Serial data 7.917144 8.25E-05 0x22

        Async Serial data 7.917231 8.25E-05 0x7D

        Async Serial data 7.917318 8.25E-05 0x26

        Async Serial data 7.917405 8.25E-05 0x7D

        Async Serial data 7.917491 8.25E-05 0x20

        Async Serial data 7.917578 8.25E-05 0x7D

        Async Serial data 7.917665 8.25E-05 0x20

        Async Serial data 7.917752 8.25E-05 0x7D

        Async Serial data 7.917839 8.25E-05 0x20

        Async Serial data 7.917925 8.25E-05 0x7D

        Async Serial data 7.918012 8.25E-05 0x20

        Async Serial data 7.918099 8.25E-05 0x7D

        Async Serial data 7.918186 8.25E-05 0x25

        Async Serial data 7.918273 8.25E-05 0x7D

        Async Serial data 7.918359 8.25E-05 0x26

        Async Serial data 7.918446 8.25E-05 0x26

        Async Serial data 7.918533 8.25E-05 0xA6

        Async Serial data 7.91862 8.25E-05 0x32

        Async Serial data 7.918707 8.25E-05 0x2F

        Async Serial data 7.918793 8.25E-05 0x7D

        Async Serial data 7.91888 8.25E-05 0x27

        Async Serial data 7.918967 8.25E-05 0x7D

        Async Serial data 7.919054 8.25E-05 0x22

        Async Serial data 7.919141 8.25E-05 0x7D

        Async Serial data 7.919227 8.25E-05 0x28

        Async Serial data 7.919314 8.25E-05 0x7D

        Async Serial data 7.919401 8.25E-05 0x22

        Async Serial data 7.919488 8.25E-05 0x46

        Async Serial data 7.919575 8.25E-05 0xDA

        Async Serial data 7.919661 8.25E-05 0x7E

        Async Serial [1] data 7.9253 8.25E-05 0xFF

        Async Serial [1] data 7.925388 8.25E-05 0x7D

        Async Serial [1] data 7.925476 8.25E-05 0x23

        Async Serial [1] data 7.925564 8.25E-05 0xC0

        Async Serial [1] data 7.925652 8.25E-05 0x21

        Async Serial [1] data 7.92574 8.25E-05 0x7D

        Async Serial [1] data 7.925828 8.25E-05 0x22

        Async Serial [1] data 7.925916 8.25E-05 0xE6

        Async Serial [1] data 7.926004 8.25E-05 0x7D

        Async Serial [1] data 7.926092 8.25E-05 0x20

        Async Serial [1] data 7.92618 8.25E-05 0x7D

        Async Serial [1] data 7.926268 8.25E-05 0x34

        Async Serial [1] data 7.926356 8.25E-05 0x7D

        Async Serial [1] data 7.926444 8.25E-05 0x22

        Async Serial [1] data 7.926532 8.25E-05 0x7D

        Async Serial [1] data 7.92662 8.25E-05 0x26

        Async Serial [1] data 7.926708 8.25E-05 0x7D

        Async Serial [1] data 7.926796 8.25E-05 0x20

        Async Serial [1] data 7.926884 8.25E-05 0x7D

        Async Serial [1] data 7.926972 8.25E-05 0x20

        Async Serial [1] data 7.92706 8.25E-05 0x7D

        Async Serial [1] data 7.927149 8.25E-05 0x20

        Async Serial [1] data 7.927237 8.25E-05 0x7D

        Async Serial [1] data 7.927325 8.25E-05 0x20

        Async Serial [1] data 7.927413 8.25E-05 0x7D

        Async Serial [1] data 7.927501 8.25E-05 0x25

        Async Serial [1] data 7.927589 8.25E-05 0x7D

        Async Serial [1] data 7.927677 8.25E-05 0x26

        Async Serial [1] data 7.927765 8.25E-05 0x26

        Async Serial [1] data 7.927853 8.25E-05 0xA6

        Async Serial [1] data 7.927941 8.25E-05 0x32

        Async Serial [1] data 7.928029 8.25E-05 0x2F

        Async Serial [1] data 7.928117 8.25E-05 0x7D

        Async Serial [1] data 7.928205 8.25E-05 0x27

        Async Serial [1] data 7.928293 8.25E-05 0x7D

        Async Serial [1] data 7.928381 8.25E-05 0x22

        Async Serial [1] data 7.928469 8.25E-05 0x7D

        Async Serial [1] data 7.928557 8.25E-05 0x28

        Async Serial [1] data 7.928645 8.25E-05 0x7D

        Async Serial [1] data 7.928733 8.25E-05 0x22

        Async Serial [1] data 7.928821 8.25E-05 0xAD

        Async Serial [1] data 7.928909 8.25E-05 0xB3

        Async Serial [1] data 7.928997 8.25E-05 0x7E

        Async Serial [1] data 7.929411 8.25E-05 0xFF

        Async Serial [1] data 7.929499 8.25E-05 0x03

        Async Serial [1] data 7.929587 8.25E-05 0x80

        Async Serial data 7.929658 8.25E-05 0x7E

        Async Serial [1] data 7.929675 8.25E-05 0x21

        Async Serial data 7.929744 8.25E-05 0xFF

        Async Serial [1] data 7.929763 8.25E-05 0x01

        Async Serial data 7.929831 8.25E-05 0x7D

        Async Serial [1] data 7.929851 8.25E-05 0x01

        Async Serial data 7.929918 8.25E-05 0x23

        Async Serial [1] data 7.929939 8.25E-05 0x00

        Async Serial data 7.930005 8.25E-05 0xC0

        Async Serial [1] data 7.930027 8.25E-05 0x0A

        Async Serial data 7.930092 8.25E-05 0x21

        Async Serial [1] data 7.930115 8.25E-05 0x03

        Async Serial data 7.930178 8.25E-05 0x7D

        Async Serial [1] data 7.930203 8.25E-05 0x06

        Async Serial data 7.930265 8.25E-05 0x2B

        Async Serial [1] data 7.930291 8.25E-05 0x00

        Async Serial data 7.930352 8.25E-05 0xE7

        Async Serial [1] data 7.930379 8.25E-05 0x00

        Async Serial data 7.930439 8.25E-05 0x7D

        Async Serial [1] data 7.930467 8.25E-05 0x00

        Async Serial data 7.930526 8.25E-05 0x20

        Async Serial [1] data 7.930555 8.25E-05 0x00

        Async Serial data 7.930612 8.25E-05 0x7D

        Async Serial data 7.930699 8.25E-05 0x28

        Async Serial data 7.930786 8.25E-05 0x26

        Async Serial data 7.930873 8.25E-05 0xA6

        Async Serial data 7.93096 8.25E-05 0x32

        Async Serial data 7.931046 8.25E-05 0x2F

        Async Serial data 7.931133 8.25E-05 0x74

        Async Serial data 7.93122 8.25E-05 0xC1

        Async Serial data 7.931307 8.25E-05 0x7E

        Async Serial [1] data 7.931541 8.25E-05 0x13

        Async Serial [1] data 7.931629 8.25E-05 0x28

        Async Serial [1] data 7.931717 8.25E-05 0x7E

        Async Serial data 7.93236 8.25E-05 0x7E

        Async Serial data 7.932447 8.25E-05 0x80

        Async Serial data 7.932534 8.25E-05 0x21

        Async Serial data 7.93262 8.25E-05 0x01

        Async Serial data 7.932707 8.25E-05 0xFD

        Async Serial data 7.932794 8.25E-05 0x00

        Async Serial data 7.932881 8.25E-05 0x04

        Async Serial data 7.932968 8.25E-05 0x2C

        Async Serial data 7.933054 8.25E-05 0xB0

        Async Serial data 7.933141 8.25E-05 0x7E

        Async Serial data 7.933228 8.25E-05 0x7E

        Async Serial data 7.933315 8.25E-05 0x80

        Async Serial data 7.933402 8.25E-05 0x21

        Async Serial data 7.933488 8.25E-05 0x03

        Async Serial data 7.933575 8.25E-05 0x01

        Async Serial data 7.933662 8.25E-05 0x00

        Async Serial data 7.933749 8.25E-05 0x0A

        Async Serial data 7.933836 8.25E-05 0x03

        Async Serial data 7.933922 8.25E-05 0x06

        Async Serial data 7.934009 8.25E-05 0x0A

        Async Serial data 7.934096 8.25E-05 0x81

        Async Serial data 7.934183 8.25E-05 0x4B

        Async Serial data 7.93427 8.25E-05 0x67

        Async Serial data 7.934356 8.25E-05 0xCA

        Async Serial data 7.934443 8.25E-05 0xA1

        Async Serial data 7.93453 8.25E-05 0x7E

        Async Serial [1] data 7.939163 8.25E-05 0xFF

        Async Serial [1] data 7.939251 8.25E-05 0x03

        Async Serial [1] data 7.939339 8.25E-05 0x80

        Async Serial [1] data 7.939427 8.25E-05 0x21

        Async Serial [1] data 7.939515 8.25E-05 0x03

        Async Serial [1] data 7.939603 8.25E-05 0xFD

        Async Serial [1] data 7.939691 8.25E-05 0x00

        Async Serial [1] data 7.939779 8.25E-05 0x0A

        Async Serial [1] data 7.939867 8.25E-05 0x03

        Async Serial [1] data 7.939955 8.25E-05 0x06

        Async Serial [1] data 7.940043 8.25E-05 0x00

        Async Serial [1] data 7.940131 8.25E-05 0x00

        Async Serial [1] data 7.940219 8.25E-05 0x00

        Async Serial [1] data 7.940307 8.25E-05 0x00

        Async Serial [1] data 7.940395 8.25E-05 0x6B

        Async Serial [1] data 7.940483 8.25E-05 0x1A

        Async Serial [1] data 7.940571 8.25E-05 0x7E

        Async Serial [1] data 7.941107 8.25E-05 0xFF

        Async Serial [1] data 7.941195 8.25E-05 0x03

        Async Serial data 7.9412 8.25E-05 0x7E

        Async Serial [1] data 7.941283 8.25E-05 0x80

        Async Serial data 7.941287 8.25E-05 0x80

        Async Serial [1] data 7.941371 8.25E-05 0x21

        Async Serial data 7.941374 8.25E-05 0x21

        Async Serial [1] data 7.94146 8.25E-05 0x01

        Async Serial data 7.94146 8.25E-05 0x01

        Async Serial data 7.941547 8.25E-05 0xFE

        Async Serial [1] data 7.941548 8.25E-05 0x02

        Async Serial data 7.941634 8.25E-05 0x00

        Async Serial [1] data 7.941636 8.25E-05 0x00

        Async Serial data 7.941721 8.25E-05 0x04

        Async Serial data 7.941808 8.25E-05 0x48

        Async Serial data 7.941894 8.25E-05 0x5F

        Async Serial data 7.941981 8.25E-05 0x7E

        Async Serial [1] data 7.942683 8.25E-05 0x0A

        Async Serial [1] data 7.942771 8.25E-05 0x03

        Async Serial [1] data 7.942859 8.25E-05 0x06

        Async Serial [1] data 7.942947 8.25E-05 0x0A

        Async Serial [1] data 7.943035 8.25E-05 0x81

        Async Serial [1] data 7.943123 8.25E-05 0x4B

        Async Serial [1] data 7.943211 8.25E-05 0x67

        Async Serial [1] data 7.943299 8.25E-05 0xFD

        Async Serial [1] data 7.943387 8.25E-05 0xC1

        Async Serial [1] data 7.943475 8.25E-05 0x7E

        Async Serial data 7.944092 8.25E-05 0x7E

        Async Serial data 7.944178 8.25E-05 0x80

        Async Serial data 7.944265 8.25E-05 0x21

        Async Serial data 7.944352 8.25E-05 0x02

        Async Serial data 7.944439 8.25E-05 0x02

        Async Serial data 7.944526 8.25E-05 0x00

        Async Serial data 7.944612 8.25E-05 0x0A

        Async Serial data 7.944699 8.25E-05 0x03

        Async Serial data 7.944786 8.25E-05 0x06

        Async Serial data 7.944873 8.25E-05 0x0A

        Async Serial data 7.94496 8.25E-05 0x81

        Async Serial data 7.945046 8.25E-05 0x4B

        Async Serial data 7.945133 8.25E-05 0x67

        Async Serial data 7.94522 8.25E-05 0xEA

        Async Serial data 7.945307 8.25E-05 0x5B

        Async Serial data 7.945394 8.25E-05 0x7E

        Async Serial [1] data 7.949159 8.25E-05 0xFF

        Async Serial [1] data 7.949247 8.25E-05 0x03

        Async Serial [1] data 7.949335 8.25E-05 0x80

        Async Serial [1] data 7.949423 8.25E-05 0x21

        Async Serial [1] data 7.949511 8.25E-05 0x02

        Async Serial [1] data 7.949599 8.25E-05 0xFE

        Async Serial [1] data 7.949687 8.25E-05 0x00

        Async Serial [1] data 7.949775 8.25E-05 0x04

        Async Serial [1] data 7.949863 8.25E-05 0x3E

        Async Serial [1] data 7.949951 8.25E-05 0x54

        Async Serial [1] data 7.950039 8.25E-05 0x7E




  Op ma 7 jun. 2021 om 16:19 schreef Bas Prins <bas.prins3@gmail.com>:

    Dear,


    I was looking at the data being sent/received over uart when ppp is being negotiated. I was surprised to see that the received byte stream is always wrapped in 0x7e bytes (leading + trailing).



    But for some reason this is not the case for the bytes lwip sends (/provides to my sio_write function). Even stronger, sometimes it does start with a leading 0x7e, sometimes it doesn't.



    On the wiki I read:


    "PPP packets all start and end with 0x7E. If you don't see these, something is wrong with your low level driver"


    When I look at fsm.c where the PPP header is created, I don't see 0x7e being added as part of the opening header.



    pppos works, lwip works, I can open sockets, download from FTP, etc. So what's the deal with this? Should I investigate further and is there a bug sitting in my code? Or is this "perfectly normal" behavior and is the wiki wrong?


    I added the logic analyzer export to this email.


    Hopefully someone can shed some light on this.


    best regards, bas













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