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SubjectRe: Telecom Clock driver for MPCBL0010 ATCA compute blade.
Date
On Wednesday 31 August 2005 12:11, Pavel Machek wrote:
> Hi!
>
> > The following is a driver I would like to see included in the base kernel.
> >
> > It allows OS controll of a device that synchronizes signaling hardware
across a ATCA chassis.
> >
> > The telecom clock hardware doesn't interact much with the operating
system, and is controlled
> > via registers in the FPGA on the hardware. It is hardware that is unique
to this computer.
>
> Now... it is probably not feasible, but: why does it need special interface
to userland?
> Could not it simply act as yet another timesource, and be controlled via
get/settimeofday?
>

The telcom clock is a special circuit, line card PLL, that provids a mechanism
for synchronization of hardware across the backplane of a chassis of multiple
computers with similar specail curcits. In this case the synchronization
signals get routed to multiple places, typically to pins on expansion slots
for hardware that knows what to do with this signal. (SONET, G.813, stratum
3...) and similar signaling applications found in telcom sites can use this
type of thing.

The actual device is hidden behind the FPGA on the motherboar, and is
connected to the FPGA via I2C. This driver only talks to the FPGA registers.

I suppose it could be configured to have the FPGA fire an interrupt ever ytime
some count of clocks come in off the back plane. The hardware really wasn't
designed to do this and I would worry that as the interrupt source is really
the FPGA getting I2C / traffic from the actual telcom clock hardware that
there would be some latencies and funny business that would make it less than
good for hard core applications.

I really don't know but, it might be possible to make it "short of work" as a
time source to the OS. I'm not going to bother trying. ;)

--mgross

> Pavel

--
--mgross
BTW: This may or may not be the opinion of my employer, more likely not.
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