PPP over serial

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quiver

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Hi there,
So I've researched this a bit and I'm having trouble finding real examples. PPP over serial is - I gather - how early dial-up modems worked.. the computer handled the PPP transaction itself. PPP over some manner of serial (usually SPI) is still used for ethernet and cellular interfaces, but it appears the PPP transaction is done in the interfacing chip itself (ethernet controller or cellular controller) which spares us mere mortals having to deal with any more layers of the OSI model than we absolutely need to.

But.. if I want to do PPP (and, by extension, lwIP) over conventional RS-232 or RS-485 from a Teensy, does such a library exist, or is it hiding in an existing library and I just haven't uncovered it yet?

Thanks in advance..
 
IIRC, SLIP was used in the dial-up.

PPP, again as IIRC, is simply a format which encapsulates the packet (anything, really).

It was based on HDLC, so it used a special flag character 7E which means you need hardware to bitstuff unless you want to spend all your microprocessor time doing the bitstuffing and extraction.

I think it added about 20 or so characters which were used to frame, ID, and checksum the packet.

It's pretty easy to accept packets and strip the PPP info, as well as create the PPP info, but if you need bitstuffing -- you really need the hardware to do that for you. (Unless you've got the cycles to burn)
 
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