A2.4
About the Generic Timer
The Generic Timer can schedule events and trigger interrupts that are based on an incrementing counter
value. It generates timer events as active-LOW interrupt outputs and event streams.
The Cortex
‑
A35 processor does not include the system counter. This resides in the SoC. The system
counter value is distributed to the Cortex
‑
A35 processor with a synchronous binary encoded 64-bit bus,
CNTVALUEB[63:0]
.
Because
CNTVALUEB[63:0]
is generated from a system counter that typically operates at a slower
frequency than the processor clock,
CLKIN
, the
CNTCLKEN
input is provided.
CNTCLKEN
is
registered inside the processor and then used as a clock enable for
CNTVALUEB[63:0]
. This allows a
multicycle path to be applied to the
CNTVALUEB[63:0]
. The following figure shows the interface.
Processor
Clock gate
CNTCLKEN
register
Architectural
counter
registers
CNTVALUEB[63:0]
CNTCLKEN
Figure A2-3 Generic Timer interface
The value on
CNTVALUEB[63:0]
is required to be stable whenever the internally registered version of
the
CNTCLKEN
clock enable is asserted.
CNTCLKEN
must be synchronous and balanced with
respect to
CLKIN
and must toggle at integer ratios of the processor
CLKIN
.
Related information
A.6 Generic Timer signals
on page Appx-A-855
A2 Technical Overview
A2.4 About the Generic Timer
100236_0100_00_en
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