Merge branch 'feature/crosscore_int' into 'master'

Add cross-core int to accelerate task being awoken from another CPU.

This adds a per-CPU interrupt that can be used to poke the CPU to go do something. In this case all that is implemented is a request to yield the current task, used in case a CPU unblocks a task that runs on another CPU. This gets rid of the limitation that inter-CPU communication using queues, muxes etc can take up to a FreeRTOS tick to happen.

Specs!
Sending an in in a queue of length 1 (essentially a semaphore) as quickly as possible (just a small delay in the sender, to make sure the receiver task gets swapped out) for 10 seconds. Number indicates the amount of ints transferred

Old code:

CPU0->CPU0: 42986

CPU0->CPU1,: 2999

New code:

CPU0->CPU0: 42868

CPU0->CPU1: 62073

See merge request !155

components/esp32/include/esp_crosscore_int.h

@@ -0,0 +1,42 @@
+// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#ifndef __ESP_CROSSCORE_INT_H
+#define __ESP_CROSSCORE_INT_H
+
+
+/**
+ * Initialize the crosscore interrupt system for this CPU.
+ * This needs to be called once on every CPU that is used
+ * by FreeRTOS.
+ *
+ * If multicore FreeRTOS support is enabled, this will be
+ * called automatically by the startup code and should not
+ * be called manually.
+ */
+void esp_crosscore_int_init();
+
+
+/**
+ * Send an interrupt to a CPU indicating it should yield its
+ * currently running task in favour of a higher-priority task
+ * that presumably just woke up.
+ *
+ * This is used internally by FreeRTOS in multicore mode
+ * and should not be called by the user.
+ *
+ * @param coreID Core that should do the yielding
+ */
+void esp_crosscore_int_send_yield(int coreId);
+
+#endif