Use token bucket instead feedback rate limiting

core/examples/pc/hardware.rs

@@ -9,7 +9,7 @@ use std::sync::{
     atomic::{AtomicBool, Ordering},
     Arc, Mutex,
 };
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
+use std::time::{Duration, Instant};
 
 use rgy::{Key, Stream, VRAM_HEIGHT, VRAM_WIDTH};
 
@@ -23,6 +23,7 @@ pub struct Hardware {
     color: bool,
     gamepad: Arc<Mutex<Gilrs>>,
     gamepad_id: Option<GamepadId>,
+    instant: Instant,
 }
 
 struct Gui {
@@ -151,6 +152,7 @@ impl Hardware {
             escape,
             gamepad,
             gamepad_id: None,
+            instant: Instant::now(),
         }
     }
 
@@ -214,10 +216,7 @@ impl rgy::Hardware for Hardware {
     }
 
     fn clock(&mut self) -> u64 {
-        let epoch = SystemTime::now()
-            .duration_since(UNIX_EPOCH)
-            .expect("Couldn't get epoch");
-        epoch.as_micros() as u64
+        self.instant.elapsed().as_micros() as u64
     }
 
     fn load_ram(&mut self, size: usize) -> Vec<u8> {

core/examples/pc/main.rs

@@ -20,12 +20,9 @@ pub struct Opt {
     /// Cpu frequency
     #[structopt(short = "f", long = "freq", default_value = "4200000")]
     freq: u64,
-    /// Sampling rate for cpu frequency controller
-    #[structopt(short = "s", long = "sample", default_value = "4200")]
-    sample: u64,
-    /// Delay unit for cpu frequency controller
-    #[structopt(short = "u", long = "delayunit", default_value = "50")]
-    delay_unit: u64,
+    /// Interval to refill the token bucket for CPU rate-limiting.
+    #[structopt(short = "i", long = "interval", default_value = "20000")]
+    interval: u64,
     /// Don't adjust cpu frequency
     #[structopt(short = "n", long = "native")]
     native_speed: bool,
@@ -44,8 +41,7 @@ fn to_cfg(opt: Opt) -> rgy::Config {
     rgy::Config::new()
         .color(opt.color)
         .freq(opt.freq)
-        .sample(opt.sample)
-        .delay_unit(opt.delay_unit)
+        .rate_limit_interval(opt.interval)
         .native_speed(opt.native_speed)
 }
 

core/src/fc.rs

@@ -1,27 +1,22 @@
 use crate::hardware::HardwareHandle;
 use crate::system::Config;
-use log::*;
 
 pub struct FreqControl {
     hw: HardwareHandle,
     last: u64,
-    cycles: u64,
-    sample: u64,
-    delay: u64,
-    delay_unit: u64,
+    refill_interval: u64,
     target_freq: u64,
+    remaining_cycles: u64,
 }
 
 impl FreqControl {
     pub fn new(hw: HardwareHandle, cfg: &Config) -> Self {
         Self {
             hw,
             last: 0,
-            cycles: 0,
-            delay: 0,
-            sample: cfg.sample,
-            delay_unit: cfg.delay_unit,
+            refill_interval: cfg.rate_limit_interval,
             target_freq: cfg.freq,
+            remaining_cycles: 0,
         }
     }
 
@@ -30,35 +25,26 @@ impl FreqControl {
     }
 
     pub fn adjust(&mut self, time: usize) {
-        self.cycles += time as u64;
+        let consumed_cycles = time as u64;
 
-        for _ in 0..self.delay {
-            let _ = unsafe { core::ptr::read_volatile(&self.sample) };
-        }
-
-        if self.cycles > self.sample {
-            self.cycles -= self.sample;
+        self.try_fill();
 
-            let now = self.hw.get().borrow_mut().clock();
-            let (diff, of) = now.overflowing_sub(self.last);
-            if of || diff == 0 {
-                warn!("Overflow: {} - {}", self.last, now);
-                self.last = now;
-                return;
-            }
+        while self.remaining_cycles < consumed_cycles {
+            self.try_fill();
+        }
 
-            // get cycles per second
-            let freq = self.sample * 1_000_000 / diff;
+        self.remaining_cycles -= consumed_cycles;
+    }
 
-            debug!("Frequency: {}", freq);
+    fn try_fill(&mut self) {
+        let now = self.hw.get().borrow_mut().clock();
 
-            self.delay = if freq > self.target_freq {
-                self.delay.saturating_add(self.delay_unit)
-            } else {
-                self.delay.saturating_sub(self.delay_unit)
-            };
+        let diff = now.saturating_sub(self.last);
 
+        if diff >= self.refill_interval {
             self.last = now;
+
+            self.remaining_cycles += self.target_freq * diff / 1_000_000;
         }
     }
 }

core/src/system.rs

@@ -9,10 +9,8 @@ use log::*;
 pub struct Config {
     /// CPU frequency.
     pub(crate) freq: u64,
-    /// Cycle sampling count in the CPU frequency controller.
-    pub(crate) sample: u64,
-    /// Delay unit in CPU frequency controller.
-    pub(crate) delay_unit: u64,
+    /// Interval to refill tokens in the token bucket for CPU rate-limiting in micro-seconds.
+    pub(crate) rate_limit_interval: u64,
     /// Don't adjust CPU frequency.
     pub(crate) native_speed: bool,
     /// Emulate Gameboy Color
@@ -32,8 +30,7 @@ impl Config {
 
         Self {
             freq,
-            sample: freq / 1000,
-            delay_unit: 10,
+            rate_limit_interval: 20_000,
             native_speed: false,
             color: false,
         }
@@ -45,15 +42,9 @@ impl Config {
         self
     }
 
-    /// Set the sampling count of the CPU frequency controller.
-    pub fn sample(mut self, sample: u64) -> Self {
-        self.sample = sample;
-        self
-    }
-
-    /// Set the delay unit.
-    pub fn delay_unit(mut self, delay: u64) -> Self {
-        self.delay_unit = delay;
+    /// Interval to refill tokens in the token bucket for CPU rate-limiting in micro-seconds.
+    pub fn rate_limit_interval(mut self, interval: u64) -> Self {
+        self.rate_limit_interval = interval;
         self
     }