From a44919038c76fe01f8f7412db8c14dca47c7cc96 Mon Sep 17 00:00:00 2001
From: Eduardo Montoya <edmont@users.noreply.github.com>
Date: Wed, 17 May 2023 22:29:14 +0200
Subject: [PATCH] [csl] split min receive window into MHR ahead and after times
 (#9041)

Existing `kMinCslWindow` does not account for needed radio on time
before MHR. Solve it by splitting the configuration option into both
ahead and after minimum times.
---
 src/core/config/mac.h                         | 25 +++++++++++++------
 .../config/openthread-core-config-check.h     |  5 ++++
 src/core/mac/sub_mac.cpp                      |  4 +--
 src/core/mac/sub_mac.hpp                      |  6 ++---
 4 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/src/core/config/mac.h b/src/core/config/mac.h
index 0358b22eb..2694e0dc8 100644
--- a/src/core/config/mac.h
+++ b/src/core/config/mac.h
@@ -489,16 +489,27 @@
 #endif
 
 /**
- * @def OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON
+ * @def OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AHEAD
  *
- * The minimum CSL receive window (in microseconds) required to receive an IEEE 802.15.4 frame.
- * - Maximum frame size with preamble: 6*2+127*2 symbols
- * - AIFS: 12 symbols
- * - Maximum ACK size with preamble: 6*2+33*2 symbols
+ * The minimum time (in microseconds) before the MHR start that the radio should be in receive state and ready to
+ * properly receive in order to properly receive any IEEE 802.15.4 frame. Defaults to the duration of SHR + PHR.
  *
  */
-#ifndef OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON
-#define OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON 356 * 16
+#ifndef OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AHEAD
+#define OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AHEAD (6 * 32)
+#endif
+
+/**
+ * @def OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AFTER
+ *
+ * The minimum time (in microseconds) after the MHR start that the radio should be in receive state in order
+ * to properly receive any IEEE 802.15.4 frame. Defaults to the duration of a maximum size frame, plus AIFS,
+ * plus the duration of maximum enh-ack frame. Platforms are encouraged to improve this value for energy
+ * efficiency purposes.
+ *
+ */
+#ifndef OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AFTER
+#define OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AFTER ((127 + 6 + 39) * 32)
 #endif
 
 /**
diff --git a/src/core/config/openthread-core-config-check.h b/src/core/config/openthread-core-config-check.h
index 67976e149..5d26a6e0f 100644
--- a/src/core/config/openthread-core-config-check.h
+++ b/src/core/config/openthread-core-config-check.h
@@ -668,4 +668,9 @@
        "OPENTHREAD_CONFIG_SRP_SERVER_DEFAULT_ADDRESS_MODE."
 #endif
 
+#ifdef OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON
+#error "OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON was replaced with "\
+        "OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AHEAD and OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AFTER"
+#endif
+
 #endif // OPENTHREAD_CORE_CONFIG_CHECK_H_
diff --git a/src/core/mac/sub_mac.cpp b/src/core/mac/sub_mac.cpp
index 7d7ac1750..755931cd2 100644
--- a/src/core/mac/sub_mac.cpp
+++ b/src/core/mac/sub_mac.cpp
@@ -1195,8 +1195,8 @@ void SubMac::GetCslWindowEdges(uint32_t &aAhead, uint32_t &aAfter)
                               (Get<Radio>().GetCslAccuracy() + mCslParentAccuracy.GetClockAccuracy()) / 1000000);
     semiWindow += mCslParentAccuracy.GetUncertaintyInMicrosec() + Get<Radio>().GetCslUncertainty() * 10;
 
-    aAhead = Min(semiPeriod, semiWindow + kCslReceiveTimeAhead);
-    aAfter = Min(semiPeriod, semiWindow + kMinCslWindow);
+    aAhead = Min(semiPeriod, semiWindow + kMinReceiveOnAhead + kCslReceiveTimeAhead);
+    aAfter = Min(semiPeriod, semiWindow + kMinReceiveOnAfter);
 }
 #endif // OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
 
diff --git a/src/core/mac/sub_mac.hpp b/src/core/mac/sub_mac.hpp
index e56321058..a4c55de80 100644
--- a/src/core/mac/sub_mac.hpp
+++ b/src/core/mac/sub_mac.hpp
@@ -573,9 +573,9 @@ private:
     };
 
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
-    // CSL receive window for the longest possible frame and
-    // ack duration.
-    static constexpr uint32_t kMinCslWindow = OPENTHREAD_CONFIG_CSL_MIN_RECEIVE_ON;
+    // Radio on times needed before and after MHR time for proper frame detection
+    static constexpr uint32_t kMinReceiveOnAhead = OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AHEAD;
+    static constexpr uint32_t kMinReceiveOnAfter = OPENTHREAD_CONFIG_MIN_RECEIVE_ON_AFTER;
 
     // CSL receivers would wake up `kCslReceiveTimeAhead` earlier
     // than expected sample window. The value is in usec.