Commit 1adaeea9 authored by Phil Elwell's avatar Phil Elwell
Browse files

BCM270X_DT: Add midi-uart1 overlay 

Add a scaler to the ttyS0 clock so that requesting 38400 baud results
in an approximately 31250 baud signal. This is analagous to
midi-uart0, except for ttyS0, which may be useful on Pi3 and also
may avoid an issue with ttyAMA0 failing to synchronise to an active
data stream.

See: https://www.raspberrypi.org/forums/viewtopic.php?f=107&t=183860



Signed-off-by: default avatarPhil Elwell <phil@raspberrypi.org>
parent e54215a9

arch/arm/boot/dts/overlays/Makefile

+1 −0
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@@ -58,6 +58,7 @@ dtbo-$(CONFIG_ARCH_BCM2835) += \ 
	mcp2515-can1.dtbo \

	mcp3008.dtbo \

	midi-uart0.dtbo \

	midi-uart1.dtbo \

	mmc.dtbo \

	mpu6050.dtbo \

	mz61581.dtbo \

arch/arm/boot/dts/overlays/README

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@@ -892,6 +892,13 @@ Load: dtoverlay=midi-uart0 
Params: <None>





Name:   midi-uart1

Info:   Configures UART1 (ttyS0) so that a requested 38.4kbaud actually gets

        31.25kbaud, the frequency required for MIDI

Load:   dtoverlay=midi-uart1

Params: <None>





Name:   mmc

Info:   Selects the bcm2835-mmc SD/MMC driver, optionally with overclock

Load:   dtoverlay=mmc,<param>=<val>

arch/arm/boot/dts/overlays/midi-uart1-overlay.dts

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/dts-v1/;

/plugin/;



#include <dt-bindings/clock/bcm2835-aux.h>



/*

 * Fake a higher clock rate to get a larger divisor, and thereby a lower

 * baudrate. The real clock is 48MHz, which we scale so that requesting

 * 38.4kHz results in an actual 31.25kHz.

 *

 *   48000000*38400/31250 = 58982400

 */



/{

	compatible = "brcm,bcm2835";



	fragment@0 {

		target-path = "/clocks";

		__overlay__ {

			midi_clk: clock@5 {

				compatible = "fixed-factor-clock";

				#clock-cells = <0>;

				clocks = <&aux BCM2835_AUX_CLOCK_UART>;

				clock-mult = <38400>;

				clock-div  = <31250>;

			};

		};

	};



	fragment@1 {

		target = <&uart1>;

		__overlay__ {

			clocks = <&midi_clk>;

		};

	};



	fragment@2 {

		target = <&aux>;

		__overlay__ {

			clock-output-names = "aux_uart", "aux_spi1", "aux_spi2";

		};

	};

};