[time-nuts] Raspberry Pi NTP server

[Trent Piepho]

On Sat, Jul 11, 2020 at 7:37 PM jimlux <jimlux at earthlink.net> wrote:
>
> You might want to look into one of the "real time" linux kernels or
> other similar implementations - they might have "turned some of the
> knobs" to improve the handling of device data.

The real time kernel primarily is about trying to get closer to making
hard real time guarantees.  To put a hard maximum on latencies.  You
can't really do that on Linux, but the real time patches made it
better.  Mostly this is about finding a place where X could not happen
in time because the CPU was doing Y instead, and Y couldn't be
interrupted.  And find a way to interrupt Y so X doesn't have to wait.

One of the biggest changes was to thread all interrupts.  So that
interrupts can be interrupted.  If you are after low interrupt
latency, this actually makes things worse.  But it makes the worst
case much better than before, at the expense of the average case.


>
> There is a reason why USB support was late in coming to Linux compared
> to other devices. And there's a reason why everyone curses at serial

I thought Linux had USB support quite early.  I remember making a
cable so I could test the USB 1.0 in my 430HX based computer, the
first Intel chipset to have USB.  I believe it didn't work properly,
some kind of chipset problem.  Unless it was the 430FX, it's been so
long.  Google tells me the 430FX didn't have USB.  But I recall that
Intel's first chipset with USB had a broken controller and the
Ministry of Truth changed the advertising to "it never had USB."

A check shows there was Linux USB support in 1996, while Windows
didn't get it until 1997.  There was a big redesign of the Linux USB
stack by Linus in 1999.  I remember things working quite a bit better
after that was done.