From 495a89459f55b81dfbbe7b133993da4301d4f781 Mon Sep 17 00:00:00 2001
From: Andy Piper <github@andypiper.com>
Date: Fri, 9 Aug 2019 17:05:19 +0100
Subject: [PATCH] AP_HAL_Empty: empty implementation of HAL FFT

---
 .../AP_HAL_Empty/AP_HAL_Empty_Namespace.h     |  1 +
 libraries/AP_HAL_Empty/AP_HAL_Empty_Private.h |  1 +
 libraries/AP_HAL_Empty/DSP.h                  | 32 +++++++++++++++++++
 libraries/AP_HAL_Empty/HAL_Empty_Class.cpp    |  3 +-
 4 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 libraries/AP_HAL_Empty/DSP.h

diff --git a/libraries/AP_HAL_Empty/AP_HAL_Empty_Namespace.h b/libraries/AP_HAL_Empty/AP_HAL_Empty_Namespace.h
index 31154e304d..f264973b44 100644
--- a/libraries/AP_HAL_Empty/AP_HAL_Empty_Namespace.h
+++ b/libraries/AP_HAL_Empty/AP_HAL_Empty_Namespace.h
@@ -4,6 +4,7 @@ namespace Empty {
     class AnalogIn;
     class AnalogSource;
     class DigitalSource;
+    class DSP;
     class GPIO;
     class I2CDevice;
     class I2CDeviceManager;
diff --git a/libraries/AP_HAL_Empty/AP_HAL_Empty_Private.h b/libraries/AP_HAL_Empty/AP_HAL_Empty_Private.h
index f04aeede0f..097aa30926 100644
--- a/libraries/AP_HAL_Empty/AP_HAL_Empty_Private.h
+++ b/libraries/AP_HAL_Empty/AP_HAL_Empty_Private.h
@@ -17,3 +17,4 @@
 #include "UARTDriver.h"
 #include "Util.h"
 #include "Flash.h"
+#include "DSP.h"
diff --git a/libraries/AP_HAL_Empty/DSP.h b/libraries/AP_HAL_Empty/DSP.h
new file mode 100644
index 0000000000..0bb5817376
--- /dev/null
+++ b/libraries/AP_HAL_Empty/DSP.h
@@ -0,0 +1,32 @@
+/*
+ * This file is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Code by Andy Piper
+ */
+#pragma once
+
+#include "AP_HAL_Empty.h"
+
+class Empty::DSP : public AP_HAL::DSP {
+#if HAL_WITH_DSP
+public:
+    virtual FFTWindowState* fft_init(uint16_t window_size, uint16_t sample_rate) override { return nullptr; }
+    virtual void fft_start(FFTWindowState* state, const float* samples, uint16_t buffer_index, uint16_t buffer_size) override {}
+    virtual uint16_t fft_analyse(FFTWindowState* state, uint16_t start_bin, uint16_t end_bin, uint8_t harmonics, float noise_att_cutoff) override { return 0; }
+protected:
+    virtual void vector_max_float(const float* vin, uint16_t len, float* maxValue, uint16_t* maxIndex) const override {}
+    virtual void vector_scale_float(const float* vin, float scale, float* vout, uint16_t len) const override {}
+#endif // HAL_WITH_DSP
+};
+
diff --git a/libraries/AP_HAL_Empty/HAL_Empty_Class.cpp b/libraries/AP_HAL_Empty/HAL_Empty_Class.cpp
index 484feb45aa..3b7c570523 100644
--- a/libraries/AP_HAL_Empty/HAL_Empty_Class.cpp
+++ b/libraries/AP_HAL_Empty/HAL_Empty_Class.cpp
@@ -43,7 +43,8 @@ HAL_Empty::HAL_Empty() :
         &schedulerInstance,
         &utilInstance,
         &opticalFlowDriver,
-        &flashDriver)
+        &flashDriver,
+        nullptr)            /* no DSP */
 {}
 
 void HAL_Empty::run(int argc, char* const argv[], Callbacks* callbacks) const