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* ARM architected timer
ARM cores may have a per-core architected timer, which provides per-cpu timers,
or a memory mapped architected timer, which provides up to 8 frames with a
physical and optional virtual timer per frame.
The per-core architected timer is attached to a GIC to deliver its
per-processor interrupts via PPIs. The memory mapped timer is attached to a GIC
to deliver its interrupts via SPIs.
** CP15 Timer node properties:
- compatible : Should at least contain one of
"arm,armv7-timer"
"arm,armv8-timer"
- interrupts : Interrupt list for secure, non-secure, virtual and
hypervisor timers, in that order.
- clock-frequency : The frequency of the main counter, in Hz. Should be present
only where necessary to work around broken firmware which does not configure
CNTFRQ on all CPUs to a uniform correct value. Use of this property is
strongly discouraged; fix your firmware unless absolutely impossible.
- always-on : a boolean property. If present, the timer is powered through an
always-on power domain, therefore it never loses context.
- fsl,erratum-a008585 : A boolean property. Indicates the presence of
QorIQ erratum A-008585, which says that reading the counter is
unreliable unless the same value is returned by back-to-back reads.
This also affects writes to the tval register, due to the implicit
counter read.
** Optional properties:
- arm,cpu-registers-not-fw-configured : Firmware does not initialize
any of the generic timer CPU registers, which contain their
architecturally-defined reset values. Only supported for 32-bit
systems which follow the ARMv7 architected reset values.
- arm,no-tick-in-suspend : The main counter does not tick when the system is in
low-power system suspend on some SoCs. This behavior does not match the
Architecture Reference Manual's specification that the system counter "must
be implemented in an always-on power domain."
Example:
timer {
compatible = "arm,cortex-a15-timer",
"arm,armv7-timer";
interrupts = <1 13 0xf08>,
<1 14 0xf08>,
<1 11 0xf08>,
<1 10 0xf08>;
clock-frequency = <100000000>;
};
** Memory mapped timer node properties:
- compatible : Should at least contain "arm,armv7-timer-mem".
- clock-frequency : The frequency of the main counter, in Hz. Should be present
only when firmware has not configured the MMIO CNTFRQ registers.
- reg : The control frame base address.
Note that #address-cells, #size-cells, and ranges shall be present to ensure
the CPU can address a frame's registers.
A timer node has up to 8 frame sub-nodes, each with the following properties:
- frame-number: 0 to 7.
- interrupts : Interrupt list for physical and virtual timers in that order.
The virtual timer interrupt is optional.
- reg : The first and second view base addresses in that order. The second view
base address is optional.
- status : "disabled" indicates the frame is not available for use. Optional.
Example:
timer@f0000000 {
compatible = "arm,armv7-timer-mem";
#address-cells = <1>;
#size-cells = <1>;
ranges;
reg = <0xf0000000 0x1000>;
clock-frequency = <50000000>;
frame@f0001000 {
frame-number = <0>
interrupts = <0 13 0x8>,
<0 14 0x8>;
reg = <0xf0001000 0x1000>,
<0xf0002000 0x1000>;
};
frame@f0003000 {
frame-number = <1>
interrupts = <0 15 0x8>;
reg = <0xf0003000 0x1000>;
status = "disabled";
};
};
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