add SPI slave support

Set up SPI slave transactions for entries in the SPI send queue.
Add a header to each SPI datagram that includes a CRC16,
the type and the size of the message that follows.

Does not act on received bytes (yet).

Signed-off-by: Christian Ambach <christian.ambach@deutschebahn.com>

include/globals.h

@@ -66,10 +66,6 @@ extern TaskHandle_t irqHandlerTask, wifiSwitchTask;
 #include "lorawan.h"
 #endif
 
-#ifdef HAS_SPI
-#include "spisend.h"
-#endif
-
 #ifdef HAS_DISPLAY
 #include "display.h"
 #endif

include/spisend.h

@@ -1,9 +0,0 @@
-#ifndef _SPISEND_H
-#define _SPISEND_H
-
-extern TaskHandle_t SpiTask;
-extern QueueHandle_t SPISendQueue;
-
-void spi_loop(void *pvParameters);
-
-#endif

include/spislave.h

@@ -0,0 +1,36 @@
+/*
+
+//////////////////////// ESP32-Paxcounter \\\\\\\\\\\\\\\\\\\\\\\\\\
+
+Copyright  2018 Christian Ambach <christian.ambach@deutschebahn.com>
+
+   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.
+
+NOTICE:
+Parts of the source files in this repository are made available under different
+licenses. Refer to LICENSE.txt file in repository for more details.
+
+*/
+#ifndef _SPISLAVE_H
+#define _SPISLAVE_H
+
+#include "globals.h"
+
+esp_err_t spi_init();
+
+void spi_enqueuedata(uint8_t messageType, MessageBuffer_t *message);
+void spi_queuereset();
+
+void spi_housekeeping();
+
+#endif // _SPISLAVE_H