[TUHS] Origins of PPP

Lawrence Stewart stewart at serissa.com
Fri Dec 6 12:05:37 AEST 2019

At the other end of PPP history, I’ve always felt that the best part of IP is that it will run, more or less, over a piece of wet string.

In 2006 at SiCortex we were building a modest supercomputer with 972 six-core MIPS-64 chips connected by a rather nice high speed interconnect.  The chips were booted over JTAG, which is another story, but in addition the chip had a “communications register” that could be written and read in I/O space from the kernel and over JTAG from the module level coldfire microcontroller.

This was at first used for the console, and all 972 console streams were collected on a front end machine.  However, it was a small step from there to multiplexing the comm register to provide two serial ports.  We used the second one for PPP using a standard driver on the MIPS end and a somewhat strange JTAG driver on the coldfire end.  This scheme let us SSH into the machine nodes when the high speed interconnect needed debugging.  In spite of the bit-banging JTAG-ness of it all, it was usably fast at 100 Kbps or so.

It was much easier to spin up PPP than to write a new network driver for this low-speed application.


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