From 1b041083ab8f3908ea1d68240e9fb8a896b61236 Mon Sep 17 00:00:00 2001
From: Gunar Schorcht <gunar@schorcht.net>
Date: Thu, 1 Aug 2019 09:49:24 +0200
Subject: [PATCH] cpu/esp32: change of critical section handling in freertos

Using a mutex for critical section handling with portENTER_CRITICAL and portEXIT_CRITICAL does not work for RIOT, as this function can also be called in the interrupt context. Therefore, the given mutex is not used. Instead, the basic default FreeRTOS mechanism for critical sections is used by simply disabling interrupts. Since context switches for the ESP32 are also based on interrupts, there is no possibility that another thread will enter the critical section once the interrupts are disabled.
---
 cpu/esp32/freertos/task.c              | 17 ++++++++++++-----
 cpu/esp32/include/freertos/portmacro.h |  7 +++++--
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/cpu/esp32/freertos/task.c b/cpu/esp32/freertos/task.c
index e5d4a1bac9..11f754aee6 100644
--- a/cpu/esp32/freertos/task.c
+++ b/cpu/esp32/freertos/task.c
@@ -10,7 +10,7 @@
 
 #ifndef DOXYGEN
 
-#define ENABLE_DEBUG 0
+#define ENABLE_DEBUG (0)
 #include "debug.h"
 
 #include <string.h>
@@ -139,8 +139,14 @@ void vTaskEnterCritical( portMUX_TYPE *mux )
     /* disable interrupts */
     uint32_t state = irq_disable();
 
-    /* aquire the mutex with interrupts disabled */
-    mutex_lock(mux); /* TODO should be only a spin lock */
+    /* Locking the given mutex does not work here, as this function can also
+       be called in the interrupt context. Therefore, the given mutex is not
+       used. Instead, the basic default FreeRTOS mechanism for critical
+       sections is used by simply disabling interrupts. Since context
+       switches for the ESP32 are also based on interrupts, there is no
+       possibility that another thread will enter the critical section
+       once the interrupts are disabled. */
+    /* mutex_lock(mux); */ /* TODO should be only a spin lock */
 
     /* increment nesting counter and save old interrupt level */
     threads_arch_exts[my_pid].critical_nesting++;
@@ -157,8 +163,9 @@ void vTaskExitCritical( portMUX_TYPE *mux )
     DEBUG("%s pid=%d prio=%d mux=%p\n", __func__,
           my_pid, sched_threads[my_pid]->priority, mux);
 
-    /* release the mutex with interrupts disabled */
-    mutex_unlock(mux); /* TODO should be only a spin lock */
+    /* The given mutex is not used (see vTaskEnterCritical) and has not to
+       be unlocked here. */
+    /* mutex_unlock(mux); */ /* TODO should be only a spin lock */
 
     /* decrement nesting counter and restore old interrupt level */
     if (threads_arch_exts[my_pid].critical_nesting) {
diff --git a/cpu/esp32/include/freertos/portmacro.h b/cpu/esp32/include/freertos/portmacro.h
index 00c9b75b17..f4f6f4b70d 100644
--- a/cpu/esp32/include/freertos/portmacro.h
+++ b/cpu/esp32/include/freertos/portmacro.h
@@ -30,8 +30,8 @@ extern "C" {
 #define portMUX_TYPE                    mutex_t
 #define portMUX_INITIALIZER_UNLOCKED    MUTEX_INIT
 
-#define portENTER_CRITICAL(pm)          mutex_lock(pm)
-#define portEXIT_CRITICAL(pm)           mutex_unlock(pm)
+#define portENTER_CRITICAL(mux)         vTaskEnterCritical(mux)
+#define portEXIT_CRITICAL(mux)          vTaskExitCritical(mux)
 #define portENTER_CRITICAL_NESTED       irq_disable
 #define portEXIT_CRITICAL_NESTED        irq_restore
 
@@ -48,6 +48,9 @@ extern "C" {
 
 #define xPortGetCoreID()                PRO_CPU_NUM
 
+extern void vTaskEnterCritical(portMUX_TYPE *mux);
+extern void vTaskExitCritical(portMUX_TYPE *mux);
+
 #ifdef __cplusplus
 }
 #endif