# Class D amplifier on RoadRunner SOM

<abstract>
This article illustrates how to enable the Class D amplifier integrated inside the SAMA5D27 and how to use it on Linux
</abstract>

<img src="./speaker.jpg" width="420px">

The Audio Class D Amplifier (CLASSD) is a digital input, Pulse Width Modulated (PWM) output stereo Class D
amplifier. It features a high-quality interpolation filter embedding a digitally-controlled gain, an equalizer and a deemphasis
filter.

Embedded Characteristics

* PWM Class D Amplifier
* 16-bit Audio Data
* DSP Clocks: 12.288 and 11.2896 MHz
* Input Sampling Rates: 8, 16, 32, 48, 96, 22.05, 44.1, 88.2 kHz
* 3-band Equalizer
* De-emphasis Filter
* Digital Volume Control
* Differential or Single-ended Outputs
* Non-overlapping Circuit to Control External MOSFETs
* Supports DMA

### Kernel setup

To enable the Class D driver laubch the kernel menuconfig ([read how...](/roadrunner_compile_kernel_4_19)) and enable these drivers:

	Device Drivers > 
		Sound card support > 
			Advanced Linux Sound Architecture > 
				ALSA for SoC audio support 
					<*>   SoC Audio for the Atmel System-on-Chip
					<*>     Atmel ASoC driver for boards using CLASSD

### Device tree bindings

Definition to insert inside the __apb__ section:

	classd: classd@fc048000 {
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_classd_default>;
		/*atmel,pwm-type = "diff";*/
		atmel,pwm-type = "single";
		atmel,non-overlap-time = <0>;
		status = "okay";
	};


Definition to insert inside the __pinctrl@fc038000__ section if you are using the MMC1 bus to wire the 
MicroSD. In this case it is possible to use just the right channel:

	pinctrl_classd_default: classd_default {
		pinmux = <PIN_PB1__CLASSD_R0>,
			 <PIN_PB2__CLASSD_R1>,
			 <PIN_PB3__CLASSD_R2>,
			 <PIN_PB4__CLASSD_R3>;
		bias-pull-up;
	};

Definition to insert inside the __pinctrl@fc038000__ section if you are using the MMC0 bus to wire the 
MicroSD. In this case is possible to use both channels:

	pinctrl_classd_default: classd_default {
		pinmux = <PIN_PB1__CLASSD_R0>,
			 <PIN_PB2__CLASSD_R1>,
			 <PIN_PB3__CLASSD_R2>,
			 <PIN_PB4__CLASSD_R3>,
			 <PIN_PA28__CLASSD_L0>,
 			 <PIN_PA29__CLASSD_L1>,
			 <PIN_PA30__CLASSD_L2>,
			 <PIN_PA31__CLASSD_L3>;
		bias-pull-up;
	};

## Hardware

To know how to implements the hardware interfaces please read the Microchip Datasheet starting from __page 1328__:

* [Microchip SAMA5D27 MCU Datasheet](http://www.microchip.com/wwwproducts/en/ATSAMA5D27)

This is the simpler solution available:

<img src="./classd_sama5d27.png">

### Test files

* [1kHz.wav](./1kHz.wav)


## Links

* [Getting Started with the SAMA5D2 Audio Subsystem](http://ww1.microchip.com/downloads/en/AppNotes/Atmel-44079-32-bit-ARM-Getting-Started-with-the-SAMA5D2-Audio-Subsystem_ApplicationNote.pdf)
* [Microchip SAMA5D27 MCU Datasheet](http://www.microchip.com/wwwproducts/en/ATSAMA5D27)

@include='adv_roadrunner'