delay / esp_delay: transparently manage recurrent scheduled functions (#8802)

Recurrent scheduled functions will always be running in background.

esp_delay()'s interval (intvl_ms) is internally kept to its highest value allowing to honor recurrent scheduled functions requirements.

It transparently allows to keep with the arduino and nonos-sdk trivial programming way and still use background services or drivers running regularly.

cores/esp8266/Schedule.cpp

@@ -17,6 +17,7 @@
 */
 
 #include <assert.h>
+#include <numeric>
 
 #include "Schedule.h"
 #include "PolledTimeout.h"
@@ -34,6 +35,7 @@ static scheduled_fn_t* sFirst = nullptr;
 static scheduled_fn_t* sLast = nullptr;
 static scheduled_fn_t* sUnused = nullptr;
 static int sCount = 0;
+static uint32_t recurrent_max_grain_mS = 0;
 
 typedef std::function<bool(void)> mRecFuncT;
 struct recurrent_fn_t
@@ -130,9 +132,39 @@ bool schedule_recurrent_function_us(const std::function<bool(void)>& fn,
     }
     rLast = item;
 
+    // grain needs to be recomputed
+    recurrent_max_grain_mS = 0;
+
     return true;
 }
 
+uint32_t compute_scheduled_recurrent_grain ()
+{
+    if (recurrent_max_grain_mS == 0)
+    {
+        if (rFirst)
+        {
+            uint32_t recurrent_max_grain_uS = rFirst->callNow.getTimeout();
+            for (auto it = rFirst->mNext; it; it = it->mNext)
+                recurrent_max_grain_uS = std::gcd(recurrent_max_grain_uS, it->callNow.getTimeout());
+            if (recurrent_max_grain_uS)
+                // round to the upper millis
+                recurrent_max_grain_mS = recurrent_max_grain_uS <= 1000? 1: (recurrent_max_grain_uS + 999) / 1000;
+        }
+
+#ifdef DEBUG_ESP_CORE
+        static uint32_t last_grain = 0;
+        if (recurrent_max_grain_mS != last_grain)
+        {
+            ::printf(":rsf %u->%u\n", last_grain, recurrent_max_grain_mS);
+            last_grain = recurrent_max_grain_mS;
+        }
+#endif
+    }
+
+    return recurrent_max_grain_mS;
+}
+
 void run_scheduled_functions()
 {
     // prevent scheduling of new functions during this run
@@ -226,6 +258,9 @@ void run_scheduled_recurrent_functions()
             }
 
             delete(to_ditch);
+
+            // grain needs to be recomputed
+            recurrent_max_grain_mS = 0;
         }
         else
         {

cores/esp8266/Schedule.h

@@ -39,6 +39,11 @@
 // scheduled function happen more often: every yield() (vs every loop()),
 // and time resolution is microsecond (vs millisecond). Details are below.
 
+// compute_scheduled_recurrent_grain() is used by delay() to give a chance to
+// all recurrent functions to run per their timing requirement.
+
+uint32_t compute_scheduled_recurrent_grain ();
+
 // scheduled functions called once:
 //
 // * internal queue is FIFO.

cores/esp8266/core_esp8266_main.cpp

@@ -22,6 +22,9 @@
 
 //This may be used to change user task stack size:
 //#define CONT_STACKSIZE 4096
+
+#include <numeric>
+
 #include <Arduino.h>
 #include "Schedule.h"
 extern "C" {
@@ -165,10 +168,18 @@ extern "C" void esp_delay(unsigned long ms) __attribute__((weak, alias("__esp_de
 bool esp_try_delay(const uint32_t start_ms, const uint32_t timeout_ms, const uint32_t intvl_ms) {
     uint32_t expired = millis() - start_ms;
     if (expired >= timeout_ms) {
-        return true;
+        return true; // expired
     }
-    esp_delay(std::min((timeout_ms - expired), intvl_ms));
-    return false;
+
+    // compute greatest chunked delay with respect to scheduled recurrent functions
+    uint32_t grain_ms = std::gcd(intvl_ms, compute_scheduled_recurrent_grain());
+
+    // recurrent scheduled functions will be called from esp_delay()->esp_suspend()
+    esp_delay(grain_ms > 0 ?
+        std::min((timeout_ms - expired), grain_ms):
+        (timeout_ms - expired));
+
+    return false; // expiration must be checked again
 }
 
 extern "C" void __yield() {

cores/esp8266/core_esp8266_wiring.cpp

@@ -34,7 +34,9 @@ static uint32_t micros_overflow_count = 0;
 #define REPEAT 1
 
 void __delay(unsigned long ms) {
-    esp_delay(ms);
+    // Use API letting recurrent scheduled functions run in background
+    // but stay blocked in delay until ms is expired.
+    esp_delay(ms, [](){ return true; });
 }
 
 void delay(unsigned long ms) __attribute__ ((weak, alias("__delay"))); 

cores/esp8266/coredecls.h

@@ -1,6 +1,5 @@
 
-#ifndef __COREDECLS_H
-#define __COREDECLS_H
+#pragma once
 
 #include "core_esp8266_features.h"
 
@@ -55,14 +54,15 @@ inline void esp_suspend(T&& blocked) {
 // Try to delay until timeout_ms has expired since start_ms.
 // Returns true if timeout_ms has completely expired on entry.
 // Otherwise returns false after delaying for the relative
-// remainder of timeout_ms, or an absolute intvl_ms, whichever is shorter.
+// remainder of timeout_ms, or an absolute intvl_ms, whichever is shorter
+// and possibly amended by recurrent scheduled functions timing grain.
 // The delay may be asynchronously cancelled, before that timeout is reached.
 bool esp_try_delay(const uint32_t start_ms, const uint32_t timeout_ms, const uint32_t intvl_ms);
 
 // This overload of esp_delay() delays for a duration of at most timeout_ms milliseconds.
-// Whenever it is resumed, as well as every intvl_ms millisconds, it performs
-// the blocked callback, and if that returns true, it keeps delaying for the remainder
-// of the original timeout_ms period.
+// Whenever it is resumed, as well as at most every intvl_ms millisconds and depending on
+// recurrent scheduled functions, it performs the blocked callback, and if that returns true,
+// it keeps delaying for the remainder of the original timeout_ms period.
 template <typename T>
 inline void esp_delay(const uint32_t timeout_ms, T&& blocked, const uint32_t intvl_ms) {
     const auto start_ms = millis();
@@ -79,5 +79,3 @@ inline void esp_delay(const uint32_t timeout_ms, T&& blocked) {
 }
 
 #endif // __cplusplus
-
-#endif // __COREDECLS_H