Oversample (#1336)

* WIP Oversample cleanup

* WIP

* WIP

* WIP dynamic interpolation

* WIP cleanup

* Fix math errors

* Add some optional assertions

* Add support for x32 interpolation

* Update proc_replay.cpp

Typo

firmware/common/buffer.hpp

@@ -49,6 +49,7 @@ using Timestamp = lpc43xx::rtc::RTC;
 
 template <typename T>
 struct buffer_t {
+    using Type = T;
     T* const p;
     const size_t count;
     const uint32_t sampling_rate;

firmware/common/message.hpp

@@ -78,7 +78,7 @@ class Message {
         ReplayThreadDone = 21,
         AFSKRxConfigure = 22,
         StatusRefresh = 23,
-        SamplerateConfig = 24,
+        SampleRateConfig = 24,
         BTLERxConfigure = 25,
         NRFRxConfigure = 26,
         TXProgress = 27,
@@ -111,7 +111,6 @@ class Message {
         APRSRxConfigure = 54,
         SpectrumPainterBufferRequestConfigure = 55,
         SpectrumPainterBufferResponseConfigure = 56,
-        OversampleRateConfig = 57,
         MAX
     };
 
@@ -799,32 +798,37 @@ class RetuneMessage : public Message {
     uint32_t range = 0;
 };
 
-class SamplerateConfigMessage : public Message {
-   public:
-    constexpr SamplerateConfigMessage(
-        const uint32_t sample_rate)
-        : Message{ID::SamplerateConfig},
-          sample_rate(sample_rate) {
-    }
-
-    const uint32_t sample_rate = 0;
-};
-
-/* Controls decimation handling in proc_capture. */
+/* Oversample/Interpolation sample rate multipliers. */
 enum class OversampleRate : uint8_t {
-    Rate8x = 8,
-    Rate16x = 16,
+    /* Use either to indicate there's no oversampling needed. */
+    None = 1,
+    x1 = None,
+
+    // 4x would make sense to have, but need to ensure it doesn't
+    // overrun the IQ read buffer in proc_replay.
+
+    /* Oversample rate of 8 times the sample rate. */
+    x8 = 8,
+
+    /* Oversample rate of 16 times the sample rate. */
+    x16 = 16,
+
+    /* Oversample rate of 32 times the sample rate. */
+    x32 = 32,
 };
 
-class OversampleRateConfigMessage : public Message {
+class SampleRateConfigMessage : public Message {
    public:
-    constexpr OversampleRateConfigMessage(
+    constexpr SampleRateConfigMessage(
+        uint32_t sample_rate,
         OversampleRate oversample_rate)
-        : Message{ID::OversampleRateConfig},
+        : Message{ID::SampleRateConfig},
+          sample_rate(sample_rate),
           oversample_rate(oversample_rate) {
     }
 
-    const OversampleRate oversample_rate{OversampleRate::Rate8x};
+    const uint32_t sample_rate = 0;
+    const OversampleRate oversample_rate = OversampleRate::None;
 };
 
 class AudioLevelReportMessage : public Message {

firmware/common/oversample.hpp

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2023 Kyle Reed, zxkmm
+ *
+ * This file is part of PortaPack.
+ *
+ * This program 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 2, or (at your option)
+ * any later version.
+ *
+ * This program 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; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/* Helpers for handling oversampling and interpolation. */
+
+#ifndef __OVERSAMPLE_H__
+#define __OVERSAMPLE_H__
+
+#include "message.hpp"
+#include "utility.hpp"
+
+/* TODO:
+ * The decision to oversample/interpolate should only be a baseband concern.
+ * However, the baseband can't set up the radio (M0 code), so the apps also
+ * need to know about the "actual" sample rate so the radio settings can be
+ * applied correctly. Ideally the baseband would tell the apps what the
+ * actual sample rate is. Currently the apps are telling the baseband and
+ * that feels like a separation of concerns problem. */
+
+/* HackRF suggests a minimum sample rate of 2M so a oversample rate is applied
+ * to the sample rate (pre-scale) to get the sample rate closer to that target.
+ * The baseband needs to know how to correctly decimate (or interpolate) so
+ * the set of allowed scalars is fixed (See OversampleRate enum).
+ * In testing, a minimum rate of 400kHz seems to the functional minimum.
+ */
+
+/* Gets the oversample rate for a given sample rate.
+ * The oversample rate is used to increase the sample rate to improve SNR and quality.
+ * This is also used as the interpolation rate when replaying captures. */
+inline OversampleRate get_oversample_rate(uint32_t sample_rate) {
+    if (sample_rate < 25'000) return OversampleRate::x32;
+    if (sample_rate < 50'000) return OversampleRate::x16;
+
+    return OversampleRate::x8;
+}
+
+/* Gets the actual sample rate for a given sample rate.
+ * This is the rate with the correct oversampling rate applied. */
+inline uint32_t get_actual_sample_rate(uint32_t sample_rate) {
+    return sample_rate * toUType(get_oversample_rate(sample_rate));
+}
+
+#endif /*__OVERSAMPLE_H__*/