Lowell Gilbert wrote:
> "Gilles Chanteperdrix" <[email protected]> writes:
>
>> Lopes, Alexandre wrote:
>>> Hello,
>>>
>>> I am trying to get Xenomai 3.0 rc4 with the 3.18.12 Linux Kernel and
>>> the
>>> corresponding ipipe patch to work on an ARM SoC.
>>> The device in question is a MitySoM module which is based on the
>>> Cyclone V
>>> from Altera and contains a dual core ARM Cortex A9.
>>>
>>> I have followed the "Porting Xenomai dual kernel to a new ARM SoC"
>>> guide. Even though Linux boots without any problems, Xenomai is not
>>> working.
>>>
>>> The output of dmesg | grep -E 'Xenomai|I-pipe' is the following:
>>>
>>> [ 0.000000] I-pipe, 200.000 MHz timer
>>> [ 0.123073] I-pipe, 200.000 MHz timer
>>> [ 0.249682] [Xenomai] scheduling class idle registered.
>>> [ 0.249689] [Xenomai] scheduling class rt registered.
>>> [ 0.249758] I-pipe: high-resolution clock not working
>>> [ 0.249789] [Xenomai] init failed, code -19
>>>
>>> Which seems to indicate a problem with the timer.
>>
>> Nope. clock != timer.
>>
>> On Cortex A9, the hardware timer used as clock is the "global timer"
>> normally. So, with recent kernels, you need the proper data in the
>> device
>> tree, and to enable the device in the kernel configuration. Look at what
>> the I-pipe patch does for OMAP4 and IMX-6.
>
>>> timer@fffec600 {
>>> compatible = "arm,cortex-a9-twd-timer";
>>> reg = <0xfffec600 0x100>;
>>> interrupts = <1 13 0xf04>;
>>> clocks = <&mpu_periph_clk>;
>>> };
>
> I believe that this *is* the global clock, and the settings are correct
> (although I wonder about it not having an interrupt-parent, which I get
> from Altera's hardware tools).
>
No. twd is the "timer watchdog", i.e. the cpu local timers.
The "global timer" by contrast is global to all cores.
The global timer register address is the address of the twd timer plus or
minus 0x400, I never remember.
The <mpu_periph_clk> is a clock, in the hardware sense, which indeed gets
the twds and global timer ticking (at cpufreq / 2). But this has nothing
to do with what the software calls a "clock". What the software calls a
clock is what Linux calls a clocksource, a counter that gives the current
time (usually since the boot-up).
--
Gilles.
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