Reimplement LED blinking using timer1_* functions directly, and avoid…

…ing FP math

src/led.cpp

@@ -0,0 +1,55 @@
+#include <Arduino.h>
+#include "led.h"
+
+// nb. Wemos D1 Mini onboard LED is active-low
+// TIM_DIV256 = 3 //312.5Khz (1 tick = 3.2us - 26843542.4 us max)
+
+volatile bool ledState; // the current LED state
+bool ledBlinkStarted; // whether blinking has started (ie. whether the ISR is attached)
+unsigned long ledTimeOff, ledTimeOn; // desired off/on times, in milliseconds
+uint32_t ledCountsOff, ledCountsOn; // desired off/on times, in timer counts of 3.2us
+
+IRAM_ATTR void ledTimerISR() {
+    if (ledState) {
+        ledState = false;
+        digitalWrite(LED_BUILTIN, HIGH);
+        timer1_write(ledCountsOff);
+        timer1_enable(TIM_DIV256, TIM_EDGE, TIM_SINGLE);
+    } else {
+        ledState = true;
+        digitalWrite(LED_BUILTIN, LOW);
+        timer1_write(ledCountsOn);
+        timer1_enable(TIM_DIV256, TIM_EDGE, TIM_SINGLE);
+    }
+}
+
+/**
+ * Start LED blinking at the specified rate, restarting blinking immediately
+ * if it's already running at a different blink rate. Blinking (re)starts in
+ * the ON state. Times in milliseconds.
+ */
+void blinkLED(unsigned long timeOn, unsigned long timeOff) {
+    if (!ledBlinkStarted || timeOff != ledTimeOff || timeOn != ledTimeOn) {
+        ledTimeOn = timeOn;
+        ledTimeOff = timeOff;
+        // milliseconds * 1000 = microseconds
+        // microseconds / 3.2 = ticks
+        // => milliseconds * (1000/3.2) = ticks
+        // => milliseconds * 312.5 = ticks
+        // ... and then we actually use 312, to avoid floating-point math entirely
+        ledCountsOn = timeOn * 312;
+        ledCountsOff = timeOff * 312;
+        ledState = true;
+        digitalWrite(LED_BUILTIN, LOW);
+        if (ledBlinkStarted) {
+            timer1_disable();
+            timer1_write(ledCountsOn);
+            timer1_enable(TIM_DIV256, TIM_EDGE, TIM_SINGLE);
+        } else {
+            timer1_attachInterrupt(ledTimerISR);
+            ledBlinkStarted = true;
+            timer1_write(ledCountsOn);
+            timer1_enable(TIM_DIV256, TIM_EDGE, TIM_SINGLE);
+        }
+    }
+}

src/led.h

@@ -0,0 +1,11 @@
+#ifndef ESP8266_BASIC_WIFI_LED_H
+#define ESP8266_BASIC_WIFI_LED_H
+
+/**
+ * Start LED blinking at the specified rate, restarting blinking immediately
+ * if it's already running at a different blink rate. Blinking (re)starts in
+ * the ON state. Times in milliseconds.
+ */
+void blinkLED(unsigned long timeOn, unsigned long timeOff);
+
+#endif //ESP8266_BASIC_WIFI_LED_H