4 files changed, 360 insertions, 17 deletions

diff --git a/docs/_summary.md b/docs/_summary.md
index 526caf926..acbfcfaed 100644
--- a/docs/_summary.md
+++ b/docs/_summary.md
@@ -133,6 +133,7 @@
     * [Compatible Microcontrollers](compatible_microcontrollers.md)
     * [Drivers](hardware_drivers.md)
       * [ADC Driver](adc_driver.md)
+      * [Audio Driver](audio_driver.md)
       * [I2C Driver](i2c_driver.md)
       * [SPI Driver](spi_driver.md)
       * [WS2812 Driver](ws2812_driver.md)
diff --git a/docs/audio_driver.md b/docs/audio_driver.md
new file mode 100644
index 000000000..7cd5a98d9
--- /dev/null
+++ b/docs/audio_driver.md
@@ -0,0 +1,221 @@
+# Audio Driver :id=audio-driver
+
+The [Audio feature](feature_audio.md) breaks the hardware specifics out into separate, exchangeable driver units, with a common interface to the audio-"core" - which itself handles playing songs and notes while tracking their progress in an internal state, initializing/starting/stopping the driver as needed.
+
+Not all MCUs support every available driver, either the platform-support is not there (yet?) or the MCU simply does not have the required hardware peripheral.
+
+
+## AVR :id=avr
+
+Boards built around an Atmega32U4 can use two sets of PWM capable pins, each driving a separate speaker.
+The possible configurations are:
+
+|              | Timer3      | Timer1       |
+|--------------|-------------|--------------|
+| one speaker  | C4,C5 or C6 |              |
+| one speaker  |             | B4, B5 or B7 |
+| two speakers | C4,C5 or C6 | B4, B5 or B7 |
+
+Currently there is only one/default driver for AVR based boards, which is automatically configured to:
+
+```make
+AUDIO_DRIVER = pwm_hardware
+```
+
+
+## ARM :id=arm
+
+For Arm based boards, QMK depends on ChibiOS - hence any MCU supported by the later is likely usable, as long as certain hardware peripherals are available.
+
+Supported wiring configurations, with their ChibiOS/MCU peripheral requirement are listed below;
+piezo speakers are marked with :one: for the first/primary and :two: for the secondary.
+
+  | driver       | GPTD6<br>Tim6                            | GPTD7<br>Tim7          | GPTD8<br>Tim8 | PWMD1<sup>1</sup><br>Tim1_Ch1 |
+  |--------------|------------------------------------------|------------------------|---------------|-------------------------------|
+  | dac_basic    | A4+DACD1 = :one:                         | A5+DACD2 = :one:       | state         |                               |
+  |              | A4+DACD1 = :one: + Gnd                   | A5+DACD2 = :two: + Gnd | state         |                               |
+  |              | A4+DACD1 = :two: + Gnd                   | A5+DACD2 = :one: + Gnd | state         |                               |
+  |              | A4+DACD1 = :one: + Gnd                   |                        | state         |                               |
+  |              |                                          | A5+DACD2 = :one: + Gnd | state         |                               |
+  | dac_additive | A4+DACD1 = :one: + Gnd                   |                        |               |                               |
+  |              | A5+DACD2 = :one: + Gnd                   |                        |               |                               |
+  |              | A4+DACD1 + A5+DACD2 = :one: <sup>2</sup> |                        |               |                               |
+  | pwm_software | state-update                             |                        |               | any = :one:                   |
+  | pwm hardware | state-update                             |                        |               | A8 = :one: <sup>3</sup>       |
+
+
+<sup>1</sup>: the routing and alternate functions for PWM differ sometimes between STM32 MCUs, if in doubt consult the data-sheet  
+<sup>2</sup>: one piezo connected to A4 and A5, with AUDIO_PIN_ALT_AS_NEGATIVE set  
+<sup>3</sup>: TIM1_CH1 = A8 on STM32F103C8, other combinations are possible, see Data-sheet. configured with: AUDIO_PWM_DRIVER and AUDIO_PWM_CHANNEL
+
+
+
+### DAC basic :id=dac-basic
+
+The default driver for ARM boards, in absence of an overriding configuration.
+This driver needs one Timer per enabled/used DAC channel, to trigger conversion; and a third timer to trigger state updates with the audio-core.
+
+Additionally, in the board config, you'll want to make changes to enable the DACs, GPT for Timers 6, 7 and 8:
+
+``` c
+//halconf.h:
+#define HAL_USE_DAC                 TRUE
+#define HAL_USE_GPT                 TRUE
+#include_next <halconf.h>
+```
+
+``` c
+// mcuconf.h:
+#include_next <mcuconf.h>
+#undef STM32_DAC_USE_DAC1_CH1
+#define STM32_DAC_USE_DAC1_CH1              TRUE
+#undef STM32_DAC_USE_DAC1_CH2
+#define STM32_DAC_USE_DAC1_CH2              TRUE
+#undef STM32_GPT_USE_TIM6
+#define STM32_GPT_USE_TIM6                  TRUE
+#undef STM32_GPT_USE_TIM7
+#define STM32_GPT_USE_TIM7                  TRUE
+#undef STM32_GPT_USE_TIM8
+#define STM32_GPT_USE_TIM8                  TRUE
+```
+
+?> Note: DAC1 (A4) uses TIM6, DAC2 (A5) uses TIM7, and the audio state timer uses TIM8 (configurable). 
+
+You can also change the timer used for the overall audio state by defining the driver.  For instance: 
+
+```c
+#define AUDIO_STATE_TIMER GPTD9
+```
+
+### DAC additive :id=dac-additive
+
+only needs one timer (GPTD6, Tim6) to trigger the DAC unit to do a conversion; the audio state updates are in turn triggered during the DAC callback.
+
+Additionally, in the board config, you'll want to make changes to enable the DACs, GPT for Timer 6:
+
+``` c
+//halconf.h:
+#define HAL_USE_DAC                 TRUE
+#define HAL_USE_GPT                 TRUE
+#include_next <halconf.h>
+```
+
+``` c
+// mcuconf.h:
+#include_next <mcuconf.h>
+#undef STM32_DAC_USE_DAC1_CH1
+#define STM32_DAC_USE_DAC1_CH1              TRUE
+#undef STM32_DAC_USE_DAC1_CH2
+#define STM32_DAC_USE_DAC1_CH2              TRUE
+#undef STM32_GPT_USE_TIM6
+#define STM32_GPT_USE_TIM6                  TRUE
+```
+
+### DAC Config
+
+| Define                           | Defaults                   | Description                                                --------------------------------------------------------------------------------------------- |
+| `AUDIO_DAC_SAMPLE_MAX`           | `4095U`                    | Highest value allowed. Lower value means lower volume. And 4095U is the upper limit, since this is limited to a 12 bit value. Only effects non-pregenerated samples.  |
+| `AUDIO_DAC_OFF_VALUE`            | `AUDIO_DAC_SAMPLE_MAX / 2` | The value of the DAC when notplaying anything. Some setups may require a high (`AUDIO_DAC_SAMPLE_MAX`) or low (`0`) value here.                                        |
+| `AUDIO_MAX_SIMULTANEOUS_TONES`   | __see next table__         | The number of tones that can be played simultaneously.  A value that is too high may freeze the controller or glitch out when too many tones are being played.        |
+| `AUDIO_DAC_SAMPLE_RATE`          | __see next table__         | Effective bit rate of the DAC (in hertz), higher limits simultaneous tones, and lower sacrifices quality.                                                          |
+
+There are a number of predefined quality settings that you can use, with "sane minimum" being the default.  You can use custom values by simply defining the sample rate and number of simultaneous tones, instead of using one of the listed presets. 
+
+| Define                            | Sample Rate | Simultaneous tones  |
+| `AUDIO_DAC_QUALITY_VERY_LOW`      | `11025U`    | `8`                 |
+| `AUDIO_DAC_QUALITY_LOW`           | `22040U`    | `4`                 |
+| `AUDIO_DAC_QUALITY_HIGH`          | `44100U`    | `2`                 |
+| `AUDIO_DAC_QUALITY_VERY_HIGH`     | `88200U`    | `1`                 |
+| `AUDIO_DAC_QUALITY_SANE_MINIMUM`  | `16384U`    | `8`                 |
+
+
+```c
+        /* zero crossing (or approach, whereas zero == DAC_OFF_VALUE, which can be configured to anything from 0 to DAC_SAMPLE_MAX)
+         * ============================*=*========================== AUDIO_DAC_SAMPLE_MAX
+         *                          *       *
+         *                        *           *
+         * ---------------------------------------------------------
+         *                     *                 *                  } AUDIO_DAC_SAMPLE_MAX/100
+         * --------------------------------------------------------- AUDIO_DAC_OFF_VALUE
+         *                  *                       *               } AUDIO_DAC_SAMPLE_MAX/100
+         * ---------------------------------------------------------
+         *               *
+         * *           *
+         *   *       *
+         * =====*=*================================================= 0x0
+         */
+```
+
+
+### PWM hardware :id=pwm-hardware
+
+This driver uses the ChibiOS-PWM system to produce a square-wave on specific output pins that are connected to the PWM hardware.
+The hardware directly toggles the pin via its alternate function. See your MCU's data-sheet for which pin can be driven by what timer - looking for TIMx_CHy and the corresponding alternate function.
+
+A configuration example for the STM32F103C8 would be:
+``` c
+//halconf.h:
+#define HAL_USE_PWM                 TRUE
+#define HAL_USE_PAL                 TRUE
+#define HAL_USE_GPT                 TRUE
+#include_next <halconf.h>
+```
+
+``` c
+// mcuconf.h:
+#include_next <mcuconf.h>
+#undef STM32_PWM_USE_TIM1
+#define STM32_PWM_USE_TIM1                  TRUE
+#undef STM32_GPT_USE_TIM4
+#define STM32_GPT_USE_TIM4                  TRUE
+```
+
+If we now target pin A8, looking through the data-sheet of the STM32F103C8, for the timers and alternate functions
+- TIM1_CH1 = PA8 <- alternate0
+- TIM1_CH2 = PA9
+- TIM1_CH3 = PA10
+- TIM1_CH4 = PA11
+
+with all this information, the configuration would contain these lines:
+``` c
+//config.h:
+#define AUDIO_PIN A8
+#define AUDIO_PWM_DRIVER PWMD1
+#define AUDIO_PWM_CHANNEL 1
+#define AUDIO_STATE_TIMER GPTD4
+```
+
+ChibiOS uses GPIOv1 for the F103, which only knows of one alternate function.
+On 'larger' STM32s, GPIOv2 or GPIOv3 are used; with them it is also necessary to configure `AUDIO_PWM_PAL_MODE` to the correct alternate function for the selected pin, timer and timer-channel.
+
+
+### PWM software :id=pwm-software
+
+This driver uses the PWM callbacks from PWMD1 with TIM1_CH1 to toggle the selected AUDIO_PIN in software.
+During the same callback, with AUDIO_PIN_ALT_AS_NEGATIVE set, the AUDIO_PIN_ALT is toggled inversely to AUDIO_PIN. This is useful for setups that drive a piezo from two pins (instead of one and Gnd).
+
+You can also change the timer used for software PWM by defining the driver.  For instance: 
+
+```c
+#define AUDIO_STATE_TIMER GPTD8
+```
+
+
+### Testing Notes :id=testing-notes
+
+While not an exhaustive list, the following table provides the scenarios that have been partially validated:
+
+|                          | DAC basic          | DAC additive       | PWM hardware       | PWM software       |
+|--------------------------|--------------------|--------------------|--------------------|--------------------|
+| Atmega32U4               | :o:                | :o:                | :heavy_check_mark: | :o:                |
+| STM32F103C8 (bluepill)   | :x:                | :x:                | :heavy_check_mark: | :heavy_check_mark: |
+| STM32F303CCT6 (proton-c) | :heavy_check_mark: | :heavy_check_mark: | ?                  | :heavy_check_mark: |
+| STM32F405VG              | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
+| L0xx                     | :x: (no Tim8)      | ?                  | ?                  | ?                  |
+
+
+:heavy_check_mark: : works and was tested  
+:o: : does not apply  
+:x: : not supported by MCU
+
+*Other supported ChibiOS boards and/or pins may function, it will be highly chip and configuration dependent.*
diff --git a/docs/config_options.md b/docs/config_options.md
index 9a64b9b3d..aeaaf47aa 100644
--- a/docs/config_options.md
+++ b/docs/config_options.md
@@ -67,16 +67,22 @@ This is a C header file that is one of the first things included, and will persi
   * turns on the alternate audio voices (to cycle through)
 * `#define C4_AUDIO`
   * enables audio on pin C4
+  * Deprecated. Use `#define AUDIO_PIN C4`
 * `#define C5_AUDIO`
   * enables audio on pin C5
+  * Deprecated. Use `#define AUDIO_PIN C5`
 * `#define C6_AUDIO`
   * enables audio on pin C6
+  * Deprecated. Use `#define AUDIO_PIN C6`
 * `#define B5_AUDIO`
-  * enables audio on pin B5 (duophony is enables if one of B[5-7]\_AUDIO is enabled along with one of C[4-6]\_AUDIO)
+  * enables audio on pin B5 (duophony is enabled if one of B pins is enabled along with one of C pins)
+  * Deprecated. Use `#define AUDIO_PIN B5`, or use `#define AUDIO_PIN_ALT B5` if a `C` pin is enabled with `AUDIO_PIN`
 * `#define B6_AUDIO`
-  * enables audio on pin B6 (duophony is enables if one of B[5-7]\_AUDIO is enabled along with one of C[4-6]\_AUDIO)
+  * enables audio on pin B5 (duophony is enabled if one of B pins is enabled along with one of C pins)
+  * Deprecated. Use `#define AUDIO_PIN B6`, or use `#define AUDIO_PIN_ALT B6` if a `C` pin is enabled with `AUDIO_PIN`
 * `#define B7_AUDIO`
-  * enables audio on pin B7 (duophony is enables if one of B[5-7]\_AUDIO is enabled along with one of C[4-6]\_AUDIO)
+  * enables audio on pin B5 (duophony is enabled if one of B pins is enabled along with one of C pins)
+  * Deprecated. Use `#define AUDIO_PIN B7`, or use `#define AUDIO_PIN_ALT B7` if a `C` pin is enabled with `AUDIO_PIN`
 * `#define BACKLIGHT_PIN B7`
   * pin of the backlight
 * `#define BACKLIGHT_LEVELS 3`
diff --git a/docs/feature_audio.md b/docs/feature_audio.md
index 68ba4477a..9e7ba75f5 100644
--- a/docs/feature_audio.md
+++ b/docs/feature_audio.md
@@ -1,21 +1,117 @@
 # Audio
 
-Your keyboard can make sounds! If you've got a Planck, Preonic, or basically any AVR keyboard that allows access to certain PWM-capable pins, you can hook up a simple speaker and make it beep. You can use those beeps to indicate layer transitions, modifiers, special keys, or just to play some funky 8bit tunes.
+Your keyboard can make sounds! If you've got a spare pin you can hook up a simple speaker and make it beep. You can use those beeps to indicate layer transitions, modifiers, special keys, or just to play some funky 8bit tunes.
 
-Up to two simultaneous audio voices are supported, one driven by timer 1 and another driven by timer 3.  The following pins can be defined as audio outputs in config.h:
+To activate this feature, add `AUDIO_ENABLE = yes` to your `rules.mk`.
 
-Timer 1:
-`#define B5_AUDIO`
-`#define B6_AUDIO`
-`#define B7_AUDIO`
+## AVR based boards
+On Atmega32U4 based boards, up to two simultaneous tones can be rendered.
+With one speaker connected to a PWM capable pin on PORTC driven by timer 3 and the other on one of the PWM pins on PORTB driven by timer 1.
 
-Timer 3:
-`#define C4_AUDIO`
-`#define C5_AUDIO`
-`#define C6_AUDIO`
+The following pins can be configured as audio outputs in `config.h` - for one speaker set eiter one out of:
 
-If you add `AUDIO_ENABLE = yes` to your `rules.mk`, there's a couple different sounds that will automatically be enabled without any other configuration:
+* `#define AUDIO_PIN C4`
+* `#define AUDIO_PIN C5`
+* `#define AUDIO_PIN C6`
+* `#define AUDIO_PIN B5`
+* `#define AUDIO_PIN B6`
+* `#define AUDIO_PIN B7`
 
+and *optionally*, for a second speaker, one of:
+* `#define AUDIO_PIN_ALT B5`
+* `#define AUDIO_PIN_ALT B6`
+* `#define AUDIO_PIN_ALT B7`
+
+### Wiring
+per speaker is - for example with a piezo buzzer - the black lead to Ground, and the red lead connected to the selected AUDIO_PIN for the primary; and similarly with AUDIO_PIN_ALT for the secondary.
+
+
+## ARM based boards
+for more technical details, see the notes on [Audio driver](audio_driver.md).
+
+<!-- because I'm not sure where to fit this in: https://waveeditonline.com/ -->
+### DAC (basic)
+Most STM32 MCUs have DAC peripherals, with a notable exception of the STM32F1xx series. Generally, the DAC peripheral drives pins A4 or A5. To enable DAC-based audio output on STM32 devices, add `AUDIO_DRIVER = dac_basic` to `rules.mk` and set in `config.h` either:
+
+`#define AUDIO_PIN A4` or `#define AUDIO_PIN A5`
+
+the other DAC channel can optionally be used with a secondary speaker, just set:
+
+`#define AUDIO_PIN_ALT A4` or `#define AUDIO_PIN_ALT A5`
+
+Do note though that the dac_basic driver is only capable of reproducing one tone per speaker/channel at a time, for more tones simultaneously, try the dac_additive driver.
+
+#### Wiring:
+for two piezos, for example configured as `AUDIO_PIN A4` and `AUDIO_PIN_ALT A5` would be: red lead to A4 and black to Ground, and similarly with the second one: A5 = red, and Ground = black
+
+another alternative is to drive *one* piezo with both DAC pins - for an extra "push".
+wiring red to A4 and black to A5 (or the other way round) and add `#define AUDIO_PIN_ALT_AS_NEGATIVE` to `config.h`
+
+##### Proton-C Example:
+The Proton-C comes (optionally) with one 'builtin' piezo, which is wired to A4+A5.
+For this board `config.h` would include these defines:
+
+```c
+#define AUDIO_PIN A5
+#define AUDIO_PIN_ALT A4
+#define AUDIO_PIN_ALT_AS_NEGATIVE
+```
+
+### DAC (additive)
+Another option, besides dac_basic (which produces sound through a square-wave), is to use the DAC to do additive wave synthesis.
+With a number of predefined wave-forms or by providing your own implementation to generate samples on the fly.
+To use this feature set `AUDIO_DRIVER = dac_additive` in your `rules.mk`, and select in `config.h` EITHER `#define AUDIO_PIN A4` or `#define AUDIO_PIN A5`.
+
+The used waveform *defaults* to sine, but others can be selected by adding one of the following defines to `config.h`:
+
+* `#define AUDIO_DAC_SAMPLE_WAVEFORM_SINE`
+* `#define AUDIO_DAC_SAMPLE_WAVEFORM_TRIANGLE`
+* `#define AUDIO_DAC_SAMPLE_WAVEFORM_TRAPEZOID`
+* `#define AUDIO_DAC_SAMPLE_WAVEFORM_SQUARE`
+
+Should you rather choose to generate and use your own sample-table with the DAC unit, implement `uint16_t dac_value_generate(void)` with your keyboard - for an example implementation see keyboards/planck/keymaps/synth_sample or keyboards/planck/keymaps/synth_wavetable
+
+
+### PWM (software)
+if the DAC pins are unavailable (or the MCU has no usable DAC at all, like STM32F1xx); PWM can be an alternative.
+Note that there is currently only one speaker/pin supported.
+
+set in `rules.mk`:
+
+`AUDIO_DRIVER = pwm_software` and in `config.h`: 
+`#define AUDIO_PIN C13` (can be any pin) to have the selected pin output a pwm signal, generated from a timer callback which toggles the pin in software.
+
+#### Wiring
+the usual piezo wiring: red goes to the selected AUDIO_PIN, black goes to ground.
+
+OR if you can chose to drive one piezo with two pins, for example `#define AUDIO_PIN B1`, `#define AUDIO_PIN_ALT B2` in `config.h`, with `#define AUDIO_PIN_ALT_AS_NEGATIVE` - then the red lead could go to B1, the black to B2.
+
+### PWM (hardware)
+STM32F1xx have to fall back to using PWM, but can do so in hardware; but again on currently only one speaker/pin.
+
+`AUDIO_DRIVER = pwm_hardware` in `rules.mk`, and in `config.h`:
+`#define AUDIO_PIN A8`
+`#define AUDIO_PWM_DRIVER PWMD1`
+`#define AUDIO_PWM_CHANNEL 1`
+(as well as `#define AUDIO_PWM_PAL_MODE 42` if you are on STM32F2 or larger)
+which will use Timer 1 to directly drive pin PA8 through the PWM hardware (TIM1_CH1 = PA8).
+Should you want to use the pwm-hardware on another pin and timer - be ready to dig into the STM32 data-sheet to pick the right TIMx_CHy and pin-alternate function.
+
+
+## Tone Multiplexing
+Since most drivers can only render one tone per speaker at a time (with the one exception: arm dac-additive) there also exists a "workaround-feature" that does time-slicing/multiplexing - which does what the name implies: cycle through a set of active tones (e.g. when playing chords in Music Mode) at a given rate, and put one tone at a time out through the one/few speakers that are available.
+
+To enable this feature, and configure a starting-rate, add the following defines to `config.h`:
+```c
+#define AUDIO_ENABLE_TONE_MULTIPLEXING
+#define AUDIO_TONE_MULTIPLEXING_RATE_DEFAULT 10
+```
+
+The audio core offers interface functions to get/set/change the tone multiplexing rate from within `keymap.c`.
+
+
+## Songs
+There's a couple of different sounds that will automatically be enabled without any other configuration:
 ```
 STARTUP_SONG // plays when the keyboard starts up (audio.c)
 GOODBYE_SONG // plays when you press the RESET key (quantum.c)
@@ -67,15 +163,34 @@ The available keycodes for audio are:
 * `AU_OFF` - Turn Audio Feature off
 * `AU_TOG` - Toggle Audio Feature state
 
-!> These keycodes turn all of the audio functionality on and off.  Turning it off means that audio feedback, audio clicky, music mode, etc. are disabled, completely. 
+!> These keycodes turn all of the audio functionality on and off.  Turning it off means that audio feedback, audio clicky, music mode, etc. are disabled, completely.
+
+## Tempo
+the 'speed' at which SONGs are played is dictated by the set Tempo, which is measured in beats-per-minute. Note lenghts are defined relative to that.
+The initial/default tempo is set to 120 bpm, but can be configured by setting `TEMPO_DEFAULT` in `config.c`.
+There is also a set of functions to modify the tempo from within the user/keymap code:
+```c
+void audio_set_tempo(uint8_t tempo);
+void audio_increase_tempo(uint8_t tempo_change);
+void audio_decrease_tempo(uint8_t tempo_change);
+```
 
 ## ARM Audio Volume
 
-For ARM devices, you can adjust the DAC sample values. If your board is too loud for you or your coworkers, you can set the max using `DAC_SAMPLE_MAX` in your `config.h`:
+For ARM devices, you can adjust the DAC sample values. If your board is too loud for you or your coworkers, you can set the max using `AUDIO_DAC_SAMPLE_MAX` in your `config.h`:
 
 ```c
-#define DAC_SAMPLE_MAX 65535U
+#define AUDIO_DAC_SAMPLE_MAX 4095U
 ```
+the DAC usually runs in 12Bit mode, hence a volume of 100% = 4095U
+
+Note: this only adjusts the volume aka 'works' if you stick to WAVEFORM_SQUARE, since its samples are generated on the fly - any other waveform uses a hardcoded/precomputed sample-buffer.
+
+## Voices
+Aka "audio effects", different ones can be enabled by setting in `config.h` these defines:
+`#define AUDIO_VOICES` to enable the feature, and `#define AUDIO_VOICE_DEFAULT something` to select a specific effect
+for details see quantum/audio/voices.h and .c
+
 
 ## Music Mode