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/***********************************************************************************************************************
 * Copyright (c) 2019 by the authors
 *
 * Author: André Borrmann
 * License: Apache License 2.0
 **********************************************************************************************************************/
#![doc(html_root_url = "https://docs.rs/ruspiro-timer/0.3.0")]
#![no_std]
#![feature(asm)]
//! # Timer functions
//!
//! This crate provides simple timing functions to pause the actual core for a specific amount of time.
//!
//! # Usage
//!
//! ```no_run
//! use ruspiro_timer as timer;
//!
//! fn foo() {
//!     timer::sleep(1000); // pause for 1 milli second
//!     timer::sleepcycles(200); // pause for 200 CPU cycles
//! }
//!
//! ```
//!
//! # Features
//!
//! - ``ruspiro_pi3`` is active by default and ensures the proper timer MMIO base memory address is
//! used for Raspberry Pi 3
//!

use ruspiro_register::{define_mmio_register, system::nop};

pub type Useconds = u64;

/// Pause the current execution for the given amount of micro seconds
pub fn sleep(usec: Useconds) {
    let wait_until = now() + usec;

    while !is_due(wait_until) {}
}

/// Pause the current execution for the given amount of CPU cycles
pub fn sleepcycles(cycles: u32) {
    for _ in 0..cycles {
        nop();
    }
}

// MMIO peripheral base address based on the target family provided with the custom target config file.
#[cfg(feature = "ruspiro_pi3")]
const PERIPHERAL_BASE: u32 = 0x3F00_0000;

// Base address of timer MMIO register
const TIMER_BASE: u32 = PERIPHERAL_BASE + 0x0000_3000;

define_mmio_register! [
    TIMERCLO<ReadOnly<u32>@(TIMER_BASE + 0x04)>,
    TIMERCHI<ReadOnly<u32>@(TIMER_BASE + 0x08)>
];

/// Get the current time as free running counter value of the system timer
fn now() -> Useconds {
    let t_low = TIMERCLO::Register.get() as u64;
    let t_high = TIMERCHI::Register.get() as u64;

    (t_high << 32) | t_low
}

/// Compare the given time as free running counter value with the current time.
/// Returns true if the current time is later than the time passed into this function.
fn is_due(time: Useconds) -> bool {
    if time == 0 {
        // if no valid time is given, time is always due
        true
    } else {
        // returns true if we have reached the current time (counter)
        now() >= time
    }
}