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    SubjectRe: [OT] high precision hardware (was Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt)
    On Fri, 15 Jul 2005, Paul Jakma wrote:

    > On Thu, 14 Jul 2005, Christoph Lameter wrote:
    >
    > > Linux can already provide a response time within < 3 usecs from user space
    > > using f.e. the Altix RTC driver which can generate an interrupt that then
    > > sends a signal to an application. The Altix RTC clock is supported via POSIX
    > > timer syscalls and can be accessed using CLOCK_SGI_CYCLE. This has been
    > > available in Linux since last fall and events can be specified with 50
    > > nanoseconds accurary.
    >
    > Out of curiosity, are there any cheap and 'embeddable' linux supported
    > architectures which support such response times (User or kernel space)?

    Well, just implement the proper hooks for the HPET so that you can use
    CLOCK_HPET from user space.

    > Input comes in at anywhere from 6kHz to 100kHz (variable), (T0 say),
    > requirement is to assert an output line Ta seconds after each T0, Ta needs to
    > be accurate to about 6us in the extreme case (how long the output is held has
    > similar accuracy requirement).

    Well the interrupt latency depends on many things in the linux kernel.
    Worst case is much greater than 6us. You probably need the RT patches as
    well.

    > What kind of hardware is capable of this? Even in microcontroller space it's
    > difficult to do (eg looked at some ARM microcontrollers, which still have
    > several usec of interrupt latency - even with no OS, still likely cant use
    > timers and interrupts.).

    Try HPET which is pretty standard these days.


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