From 1d51c12bc1021370ee8a68770d457cb3f115d106 Mon Sep 17 00:00:00 2001
From: Naxdy <naxdy@naxdy.org>
Date: Fri, 19 Apr 2024 14:20:14 +0200
Subject: [PATCH] feat(hid): implement lower-latency consistency algo

---
 src/gcc_hid.rs | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/gcc_hid.rs b/src/gcc_hid.rs
index e5b3bff..72bcf03 100644
--- a/src/gcc_hid.rs
+++ b/src/gcc_hid.rs
@@ -13,7 +13,7 @@ use embassy_rp::{
 };
 
 use embassy_sync::{blocking_mutex::raw::CriticalSectionRawMutex, mutex::Mutex, signal::Signal};
-use embassy_time::{Duration, Instant, Ticker, Timer};
+use embassy_time::{Duration, Instant, Timer};
 use embassy_usb::{
     class::hid::{HidReaderWriter, ReportId, RequestHandler, State},
     control::OutResponse,
@@ -361,7 +361,8 @@ pub async fn usb_transfer_task(raw_serial: [u8; 8], driver: Driver<'static, USB>
         let mut gcc_subscriber = CHANNEL_GCC_STATE.subscriber().unwrap();
 
         let mut last_report_time = Instant::now();
-        let mut ticker = Ticker::every(Duration::from_micros(8333));
+        let mut frame_ready_time = Instant::now() + Duration::from_micros(8333);
+        let mut usb_ready_time = Instant::now() + Duration::from_millis(8);
 
         loop {
             // This is what we like to call a "hack".
@@ -383,9 +384,18 @@ pub async fn usb_transfer_task(raw_serial: [u8; 8], driver: Driver<'static, USB>
                     Timer::at(last_report_time + Duration::from_micros(8100)).await;
                 }
                 InputConsistencyMode::ConsistencyHack => {
-                    // Ticker better maintains a consistent interval than Timer, so
-                    // we prefer it for consistency mode, where we send reports regularly.
-                    ticker.next().await;
+                    // Ensure we report in multiples of 1 (not in decimals, like 8.33ms)
+                    Timer::at(usb_ready_time).await;
+                    while Instant::now() < frame_ready_time {
+                        Timer::after_micros(1000).await;
+                    }
+                    // has to be done this way in case we're behind through e.g. suspends
+                    while frame_ready_time < Instant::now() {
+                        frame_ready_time += Duration::from_micros(8333);
+                    }
+                    while usb_ready_time < Instant::now() {
+                        usb_ready_time += Duration::from_millis(8);
+                    }
                 }
                 InputConsistencyMode::Original => {}
             }
@@ -404,13 +414,6 @@ pub async fn usb_transfer_task(raw_serial: [u8; 8], driver: Driver<'static, USB>
                     let polltime = currtime.duration_since(last_report_time);
                     let micros = polltime.as_micros();
                     debug!("Report written in {}us", micros);
-                    // If we're sending reports too fast in regular consistency mode, reset the ticker.
-                    // This might happen right after plug-in, or after suspend.
-                    if input_consistency_mode == InputConsistencyMode::ConsistencyHack
-                        && micros < 8150
-                    {
-                        ticker.reset()
-                    }
                     last_report_time = currtime;
                 }
                 Err(e) => warn!("Failed to send report: {:?}", e),