From 10b37cf8e3affb7f8dc7f401abf1e9b929637b67 Mon Sep 17 00:00:00 2001
From: "Earle F. Philhower, III" <Earle.Philhower.III@wdc.com>
Date: Wed, 19 Dec 2018 09:52:53 -0800
Subject: [PATCH] Add FreeStack method for ESP8266

The ESP8266 Arduino code has built in routines to get stack free.
Use them to provide accurate results in benchmarks/etc.
---
 src/FreeStack.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/FreeStack.h b/src/FreeStack.h
index c655ef61..2cc45b4c 100644
--- a/src/FreeStack.h
+++ b/src/FreeStack.h
@@ -52,6 +52,12 @@ static int FreeStack() {
   char top = 't';
   return &top - reinterpret_cast<char*>(sbrk(0));
 }
+#elif defined(ESP8266)
+static int FreeStack() {
+  int free = (int)ESP.getFreeContStack();
+  ESP.resetFreeContStack();
+  return free;
+}
 #else
 #warning FreeStack is not defined for this system.
 static int FreeStack() {