dts/bindings/timer/nuclei,systimer.yaml

# Copyright (c) 2021 TOKITA Hiroshi <tokita.hiroshi@gmail.com>
# SPDX-License-Identifier: Apache-2.0

description: |
  Nuclei System Timer

  The Nuclei system timer provides RISC-V privileged mtime and mtimecmp
  registers.

compatible: "nuclei,systimer"

include: base.yaml

properties:
  reg:
    required: true

  interrupts:
    required: true

  clk-divider:
    type: int
    description: |
      clk-divider specifies the division ratio to the CPU frequency that
      clock used by the system timer.
      This property supports the case that the system timer and CPU use
      different clock sources.
      This configuration is used sometimes for such as low power consumption.

      For example, the CPU clock frequency is 108MHz, and the system timer
      uses 27MHz, which is the CPU clock divided by 4.
      In this case, the CPU clock frequency is defined in the CPU node
      as follows

         clock-frequency = <108000000>;

      This property takes exponent of the power of 2.
      The relationship with the frequency division ratio is as
      following equation.

         division_ratio = 2^n
         n = log_2(division_ratio)

      Setting clk-divider to 2 specifies the system timer uses the clock
      that CPU clock frequency divided by (2^2=)4, or 27MHz.

      Devision ratio constants can be found in the
      dt-bindings/timer/nuclei-systimer.h header file.