Hi Andrew,
Thanks for answering this question. I was curious about interrupts
as well. If I understand you correctly, a timer exists and it is only
used when a driver or a program requests it.
So, when we come up in a basic UEFI Shell the system is essentially
tickless?
Thanks,
Stephen
Andrew Fish wrote:
>
> On May 16, 2013, at 7:16 AM, "zzhh.happy" <zzhh.ha...@163.com
> <mailto:zzhh.ha...@163.com>> wrote:
>
>> Hi all,
>>
>> I'm fresh man for studying UEFI,and there are some questions ,is there
>> anyone can help,thanks!
>> as we know there is only on interrupt that is the timer,it works as
>> the heartbeat timer.but in X86 platform i can't find the
>> timer interrupt handle function. except bellow
>> service *CoreTimerTick,*but there is a input
>> parameter *Duration,*never heard that interrupt service have input
>> parameter,if yes, who pass it in?
>> and there are my question:
>>
> UEFI does not define how the timer works, just that it exists. The UEFI
> Platform Initialization Specification 1.2.1
> <http://www.uefi.org/specs/platform_agreement> (also called PI spec)
> defines how the timer works in the edk2 http://www.uefi.org/specs/.
>
> The PI defines a set of Architectural Protocol that produce the hardware
> services needed to produce the EFI services. If you look
> in
> https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/MdeModulePkg/Core/Dxe/DxeMain/DxeProtocolNotify.c
>
> you will see the mArchProtocols array that contains a list of these
> architectural protocols, and some globals that filled in when the
> protocols are registered.
>
> So basically the CPU AP, gEfiCpuArchProtocolGuid, abstracts interrupt
> handling in a processor agnostic way (Same DXE Core source works for
> Itainum, IA32, X64, and ARM). The Timer AP, gEfiTimerArchProtocolGuid,
> depends on the CPU AP and produces the timer tick for the platform.
>> 1.in x86 platform what is the heartbeat,is it the leagcy 8254?
> It can be any timer. It is what ever Timer AP driver gets included in
> the firmware. Search for drivers installing gEfiTimerArchProtocolGuid.
>> 2.what is the interrupt vector number?
> There is not a standard. It is platform specific and set by the driver.
> Some drivers may offer a PCD config setting to change the vector.
>> 3.where is the IDT table exist in memery after the timer start ticking
> The CPU AP driver sets up the IDT. For X64/IA32 the IDT is not at a
> fixed address. Search for a driver installing gEfiCpuArchProtocolGuid.
> Note: There is an assemble instruction that lets you know the address,
> but it is probably a very bad idea to patch anything into the table
> directly as debuggers need to cooperate with the CPU AP to hook vectors,
> so you may break the debugger or the CPU AP. You can use
> gEfiCpuArchProtocolGuid services to hook an interrupt vector if that is
> what you need to do.
> There are C functions that implement common assembly instruction in the
> BaseLib. So AsmReadIdtr().
>> 4.what is the heartbeat service handle,and how it registered to the
>> cpu's interrupt verctor table.
> https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/MdeModulePkg/Core/Dxe/DxeMain/DxeProtocolNotify.c
>
> When the Timer AP service is registered the DXE Core does:
>
> gTimer->RegisterHandler (gTimer, CoreTimerTick);
>
> Which registers the DXE Cores timer callback.
>
> This is an example gEfiCpuArchProtocolGuid driver:
> https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/UefiCpuPkg/CpuDxe/
> This is not the driver you would find on a real platform as there is a
> large amount of processor specific initialization that is required, but
> it shows the general concepts.
>
> Thanks,
>
> Andrew Fish
>>
>> thanks very much.
>>
>>
>> VOID
>> EFIAPI
>> *CoreTimerTick* (
>> IN UINT64 Duration
>> )
>> /*++
>> Routine Description:
>> Called by the platform code to process a tick.
>> Arguments: Duration - The number of 100ns elasped since the last
>> call to TimerTick
>> Returns: None
>> --*/
>> {
>> IEVENT *Event;
>> // Check runtiem flag in case there are ticks while exiting boot
>> services
>> CoreAcquireLock (&mEfiSystemTimeLock);
>> // Update the system time
>> mEfiSystemTime += Duration;
>> // If the head of the list is expired, fire the timer event
>> // to process it
>> if (!IsListEmpty (&mEfiTimerList)) {
>> Event = CR (mEfiTimerList.ForwardLink, IEVENT, u.Timer.Link,
>> EVENT_SIGNATURE);
>> if (Event->u.Timer.TriggerTime <= mEfiSystemTime) {
>> CoreSignalEvent (mEfiCheckTimerEvent);
>> }
>> }
>> CoreReleaseLock (&mEfiSystemTimeLock);
>> }
>> 2013-05-16
>> ------------------------------------------------------------------------
>> zzhh.happy
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>
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