Messages in this thread | | | Date | Tue, 07 Sep 2010 11:05:07 +0200 | From | Clemens Ladisch <> | Subject | Re: Hungry for hardware timers |
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Jaswinder Singh Rajput wrote: > On Tue, Sep 7, 2010 at 1:29 PM, Clemens Ladisch <clemens@ladisch.de> wrote: >> Jaswinder Singh Rajput wrote: >>> I am investigating how many hardware timers are available for kernel, >>> system applications and user applications for x86 platforms. >> >> Why would you want to have a separate timer for your application? > > I need a programmable periodic interrupt for an embedded project.
And why do you not want to use POSIX timers for this?
>>> HPET have 3 timers : >>> T0 and T2 is already used by Linux and T1 is used for RTC >> >> T2 shouldn't be used. > > [ 0.323613] hpet: hpet_msi_capability_lookup(621): > .. > [ 0.325323] hpet: T2: CFG_l: 0x0, CFG_h: 0xf00800 > [ 0.325483] hpet: T2: CMP_l: 0xffffffff, CMP_h: 0x0 > [ 0.325639] hpet: T2 ROUTE_l: 0x0, ROUTE_h: 0x0 > [ 0.325958] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0 > [ 0.326279] hpet0: 3 comparators, 64-bit 14.318180 MHz counter > [ 0.328003] hpet: hpet_late_init(951): > .. > [ 0.331006] hpet: T2: CFG_l: 0x0, CFG_h: 0xf00800 > [ 0.331167] hpet: T2: CMP_l: 0xdfe12a, CMP_h: 0x0 > [ 0.331327] hpet: T2 ROUTE_l: 0x0, ROUTE_h: 0x0 > > As you can see after hpet_late_init(951) T2 CMP_l is changed.
Strange; nobody should be accessing this. Do you need to use it before hpet_late_init?
>> What does /proc/interrupts say? > > $ cat /proc/interrupts > CPU0 CPU1 > 0: 192286 0 IO-APIC-edge timer > 1: 1039 0 IO-APIC-edge i8042 > 8: 50 0 IO-APIC-edge rtc0 > 9: 637 1903 IO-APIC-fasteoi acpi > 12: 163 515 IO-APIC-edge i8042 > 16: 21285 0 IO-APIC-fasteoi i915, ath9k, ehci_hcd:usb1, uhci_hcd:usb2 > 17: 0 0 IO-APIC-fasteoi uhci_hcd:usb3 > 18: 0 0 IO-APIC-fasteoi uhci_hcd:usb4 > 19: 0 0 IO-APIC-fasteoi uhci_hcd:usb5 > 44: 3511 9569 PCI-MSI-edge ahci > 45: 515 1569 PCI-MSI-edge hda_intel > 46: 2 0 PCI-MSI-edge eth0
Nobody is using /dev/hpet, you should be able to grab it for T2.
> By the way why I am getting this : > > [ 568.301571] CE: hpet increased min_delta_ns to 7500 nsec > [ 568.301736] CE: hpet increased min_delta_ns to 11250 nsec > [ 568.301888] CE: hpet increased min_delta_ns to 16875 nsec
On my AMD machine, this happens only if I have C1E enabled, and only up to 11250 ns. It seems your BIOS has installed a SMI.
Regards, Clemens
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