dts/bindings/timer/riscv,machine-timer.yaml

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

description: RISC-V Machine timer

compatible: "riscv,machine-timer"

include: base.yaml

properties:
    clk-divider:
      type: int
      required: false
      description: |
        clk-divider specifies the division ratio to the CPU frequency that
        clock used by machine timer.
        This property supports the case that the machine 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 machine 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 machine 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-machine-timer.h header file.