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salix14
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PostPosted: Mon Apr 06, 2015 10:43 am    Post subject: PPP over PCIe Reply with quote

hi, I want to send ppp packets generated in linux ppp module over PCIe instead of serial port. and then through FPGA send packets out. can anyone give me a point to how can I do it? how can I send ppp packets to PCIe driver?[/topic]
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NeddySeagoon
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PostPosted: Mon Apr 06, 2015 4:41 pm    Post subject: Reply with quote

salix14,

Welcome to Gentoo.

PCIe is a serial interface. Well, single channel PCIe is anyway.
You can send PPP packets over any hardware channel you like, as long as something at both ends understanhs the encapsulating protocal.

Tell us the actual problem you want to solve, rather than your perceived solution. Someone here may know a better solution.
Indeed, there may already be an open source solution to your problem that you can build on.
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salix14
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PostPosted: Wed Apr 08, 2015 10:49 am    Post subject: Reply with quote

thanks NeddySeagoon

actually, I'm beginner in linux device driver. and I have no idea to how do this. I using RIFFA architecture for send and receive data to/from FPGA, RIFFA has library in user space to communicate with it's driver.
RIFFA site: https://sites.google.com/a/eng.ucsd.edu/matt-jacobsen/riffa
and: http://riffa.ucsd.edu/

you said that it's possible to send PPP packets over any hardware channel. how?

Is it possible to direct the output of the driver's PPP packets to a virtual file (e.g. /dev/myPPPout). Then write a user space program to read that device file and use the RIFFA user space library to send it to the FPGA? is this best solution?
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NeddySeagoon
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PostPosted: Wed Apr 08, 2015 7:55 pm    Post subject: Reply with quote

salix14,

All hardware communication links support some protocol or another. Some support several.

Pick a protocol and pack your PPP packets into it at one end and unpack it at the other end.
This may mean that you have to manage joins in the native protocol.

Lets take a real trivial example. You need to send a binary file over a data link that can only support printable ASCII characters. A space counts as a printable character.
At the transmitting end you take your binary file and reduce it to a sequence of bits.
Take the bits five at a time and add them to an ASCII space charater. Send the resulting character over the data link.
It must be a printable character as you can only have 2^5 or 32 different values.

At the receiving end, reverse the process.
There are a number of arbitary decisions to be made in the implementation but as long as both ends of the link do the same thing, it doesn't matter.
e.g. do you send ls bit first on ms bit. Which end of the file do you start ...

The above is called UUencoding/UUdecoding.
If you know that you can use the lowercase symbol set too, you can use 6 bit packing instead of 5 bit packing.
It does not matter what the physical implementation of the data link is, you have the constraint that it can only carry printable ASCII characters and the problem calls for binary data to be delivered.

Wikipedia shows more details an indicates thau UUencode is actually the 6 bit version.
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