DMA-based ADC input (microphone, analog sensor) (#1101)

Mimics the I2S/PWMAudio/Stream interface for ease of use.

* Fix non-32b DMA size transfer calculation in ABM
* Rename wasHolding to isHolding in the I2S/PWM
  It is the **current** number of bits left, not the past number.
* Add commented microphone example
* Add docs

libraries/ADCInput/src/ADCInput.cpp

@@ -0,0 +1,172 @@
+/*
+    ADCInput
+    Records ADC values (i.e. microphone, sensors) and presents an I2S-like
+    callback/immediate read interface
+
+    Copyright (c) 2023 Earle F. Philhower, III <earlephilhower@yahoo.com>
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Lesser General Public
+    License as published by the Free Software Foundation; either
+    version 2.1 of the License, or (at your option) any later version.
+
+    This library 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
+    Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public
+    License along with this library; if not, write to the Free Software
+    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include <Arduino.h>
+#include "ADCInput.h"
+#include <hardware/adc.h>
+
+ADCInput::ADCInput(pin_size_t p0, pin_size_t p1, pin_size_t p2, pin_size_t p3) {
+    _running = false;
+    setPins(p0, p1, p2, p3);
+    _freq = 48000;
+    _arb = nullptr;
+    _cb = nullptr;
+    _buffers = 8;
+    _bufferWords = 0;
+}
+
+ADCInput::~ADCInput() {
+    end();
+}
+
+bool ADCInput::setBuffers(size_t buffers, size_t bufferWords) {
+    if (_running || (buffers < 3) || (bufferWords < 8)) {
+        return false;
+    }
+    _buffers = buffers;
+    _bufferWords = bufferWords;
+    return true;
+}
+
+int ADCInput::_mask(pin_size_t p) {
+    switch (p) {
+    case 26: return 1;
+    case 27: return 2;
+    case 28: return 4;
+    case 29: return 8;
+    default: return 0;
+    }
+}
+
+bool ADCInput::setPins(pin_size_t pin0, pin_size_t pin1, pin_size_t pin2, pin_size_t pin3) {
+    if (_running) {
+        return false;
+    }
+    _pinMask = _mask(pin0) | _mask(pin1) | _mask(pin2) | _mask(pin3);
+    return true;
+}
+
+bool ADCInput::setFrequency(int newFreq) {
+    _freq = newFreq * __builtin_popcount(_pinMask); // Want to sample all channels at given frequency
+    adc_set_clkdiv(48000000.0f / _freq - 1.0f);
+    return true;
+}
+
+void ADCInput::onReceive(void(*fn)(void)) {
+    _cb = fn;
+    if (_running) {
+        _arb->setCallback(_cb);
+    }
+}
+
+bool ADCInput::begin() {
+    _running = true;
+
+    _isHolding = 0;
+
+    if (!_bufferWords) {
+        _bufferWords = 16;
+    }
+
+    // Set up the GPIOs to go to ADC
+    adc_init();
+    int cnt = 0;
+    for (int mask = 1, pin = 26; pin <= 29; mask <<= 1, pin++) {
+        if (_pinMask & mask) {
+            if (!cnt) {
+                adc_select_input(pin - 26);
+            }
+            cnt++;
+            adc_gpio_init(pin);
+        }
+    }
+    adc_set_round_robin(_pinMask);
+    adc_fifo_setup(true, true, 1, false, false);
+
+    setFrequency(_freq);
+
+    _arb = new AudioBufferManager(_buffers, _bufferWords, 0, INPUT, DMA_SIZE_16);
+    _arb->begin(DREQ_ADC, (volatile void*)&adc_hw->fifo);
+    _arb->setCallback(_cb);
+
+    adc_fifo_drain();
+
+    adc_run(true);
+
+    return true;
+}
+
+void ADCInput::end() {
+    if (_running) {
+        _running = false;
+        delete _arb;
+        _arb = nullptr;
+    }
+    adc_run(false);
+    adc_fifo_drain();
+}
+
+int ADCInput::available() {
+    if (!_running) {
+        return 0;
+    } else {
+        return _arb->available();
+    }
+}
+
+int ADCInput::read() {
+    if (!_running) {
+        return -1;
+    }
+
+    if (_hasPeeked) {
+        _hasPeeked = false;
+        return _peekSaved;
+    }
+
+    if (_isHolding <= 0) {
+        _arb->read(&_holdWord, true);
+        _isHolding = 32;
+    }
+
+    int ret = _holdWord & 0x0fff;
+    _holdWord >>= 16;
+    _isHolding -= 16;
+    return ret;
+}
+
+int ADCInput::peek() {
+    if (!_running) {
+        return -1;
+    }
+    if (!_hasPeeked) {
+        _peekSaved = read();
+        _hasPeeked = true;
+    }
+    return _peekSaved;
+}
+
+void ADCInput::flush() {
+    if (_running) {
+        _arb->flush();
+    }
+}