查看“Linux内核-摄像头驱动移植”的源代码

==实验原理==
DCMI(Digital Camera Interface)，DCMI是一个同步并行接口，能够从外部8bit、10bit、12bit或14bit的CMOS摄像头接收高速数据流，支持不同的数据格式：YCbCr4:2:2/RGB565渐进式视频和压缩数据（JPEG）。<br>

[[Image:58-1-1-1.png|640px]] <br>

FS-MP1A可以外接8bit的COM Camera，接口定义如下:

[[Image:58-1-1-2.png]] <br>

接口与MPU管脚对应关系如下：

[[Image:58-1-1-3.png]] 
[[Image:58-1-1-4.png]] <br>

[[Image:58-1-1-5.png]] 
[[Image:58-1-1-6.png]] <br>

[[Image:58-1-1-7.png]]<br>

{|class="wikitable"
|-
!原理图网络编号 !! 对应管脚 !! 管脚功能 !! 管脚功能码
|-
| DCMI_D0
| PH9
| DCMI_D0
| AF13
|-
| DCMI_D1
| PH10 
| DCMI_D0
| AF13
|-
| DCMI_D2 
| PH11 
| DCMI_D0
| AF13
|-
| DCMI_D3 
| PH12 
| DCMI_D0
| AF13
|-
| DCMI_D4 
| PH14 
| DCMI_D0
| AF13
|-
| DCMI_D5
| PI4 
| DCMI_D0
| AF13
|-
| DCMI_D6 
| PB8
| DCMI_D0
| AF13
|-
| DCMI_D7 
| PE6 
| DCMI_D0
| AF13
|-
| DCMI_RESET 
| PA3 
| GPIO
| ANALOG
|-
| DCMI_PWDN 
| PA4 
| GPIO
| ANALOG
|-
| DCMI_PIXCK
| PA6 
| DCMI_PIXCLK
| AF13
|-
| DCMI_VSYNC
| PB7
| DCMI_VSYNC
| AF13
|}
<ol>
<li>DCMI设备树节点</li>

参考文档：
<pre><nowiki>
Documentation/devicetree/bindings/media/st,stm32-dcmi.txt
Documentation/devicetree/bindings/media/video-interfaces.txt
</nowiki></pre>
内核中ST对STM32MP15x系列芯片的设备树资源了做了定义，可参见：
 arch/arm/boot/dts/stm32mp151.dtsi
stm32mp151中dcmi定义如下：
<pre><nowiki>
dcmi: dcmi@4c006000 {
	compatible = "st,stm32-dcmi";
	reg = <0x4c006000 0x400>;
	interrupts = <GIC_SPI 78 IRQ_TYPE_LEVEL_HIGH>;
	resets = <&rcc CAMITF_R>;
	clocks = <&rcc DCMI>;
	clock-names = "mclk";
	dmas = <&dmamux1 75 0x400 0xe0000001>;
	dma-names = "tx";
	status = "disabled";
};
</nowiki></pre>
上述代码只对dcmi做了基本的初始化，并没有针对不同的硬件设计做适配，所以需结合硬件补全设备树节点信息。<br>

参考帮助文档及内核中其它STM32MP157设备树中对于dcmi的定义，修改dcmi内容如下：
<pre><nowiki>
&dcmi {
	status = "okay";
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&dcmi_pins_a>;
	pinctrl-1 = <&dcmi_sleep_pins_a>;

	port {
		dcmi_0: endpoint {
			remote-endpoint = <&ov5640_0>;
			bus-width = <8>;
			hsync-active = <0>;
			vsync-active = <0>;
			pclk-sample = <1>;
			pclk-max-frequency = <77000000>;
		};
	};
};
</nowiki></pre>
由于stm32mp15-pinctrl.dtsi中对于DCMI管脚的定义与FS-MP1A实际使用管脚一致，所以无需修改

<li>CMOS Camera设备树节点</li>

FS-MP1A支持多款COMS Camera，本节以ov5640为例：<br>

参考文档：
 Documentation/devicetree/bindings/media/i2c/ov5640.txt
参考帮助文档及内核中其它STM32MP157设备树中对于ov5640的定义，修改dcmi内容如下：
<pre><nowiki>
ov5640: camera@3c {
	compatible = "ovti,ov5640";
	reg = <0x3c>;
	clocks = <&clk_ext_camera>;
	clock-names = "xclk";
	DOVDD-supply = <&v2v8>;
	powerdown-gpios = <&gpioa 4 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
	reset-gpios = <&gpioa 3 (GPIO_ACTIVE_LOW | GPIO_PUSH_PULL)>;
	rotation = <180>;
	status = "okay";

	port {
		ov5640_0: endpoint {
			remote-endpoint = <&dcmi_0>;
			bus-width = <8>;
			data-shift = <2>; /* lines 9:2 are used */
			hsync-active = <0>;
			vsync-active = <0>;
			pclk-sample = <1>;
			pclk-max-frequency = <77000000>;
	  	};
	};
};	
</nowiki></pre>
<li>2.8V电源定义</li>

前文已经说过如何添加电源节点，本节不再重复，在根节点添加&v2v8节点，内容如下：
<pre><nowiki>
v2v8_audio: regulator-v2v8 {
	compatible = "regulator-fixed";
	regulator-name = "v2v8";
	regulator-min-microvolt = <2800000>;
	regulator-max-microvolt = <2800000>;
	regulator-always-on;
	regulator-boot-on;
};
</nowiki></pre>
<li>24M时钟定义</li>

参考文档：
 Documentation/devicetree/bindings/clock/fixed-clock.yaml
参考帮助文档或内核中其他设备树文件，对于时钟的定义，增加内容如下：
<pre><nowiki>
clocks {
	clk_ext_camera: clk-ext-camera {
		#clock-cells = <0>;
		compatible = "fixed-clock";
		clock-frequency = <24000000>;
	};
};
</nowiki></pre>
</ol>

==实验目的==
熟悉基于Linux操作系统下的摄像头设备驱动移植配置过程。

==实验平台==
华清远见开发环境，FS-MP1A平台；

==实验步骤==
<ol>
<li>导入交叉编译工具链</li>
 linux@ubuntu:$ source /opt/st/stm32mp1/3.1-openstlinux-5.4-dunfell-mp1-20-06-24/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi
<li>增加DCMI设备树节点</li>

修改arch/arm/boot/dts/stm32mp15xx-fsmp1x.dtsi文件，在文件末尾添加如下内容：
<pre><nowiki>
&dcmi {
	status = "okay";
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&dcmi_pins_a>;
	pinctrl-1 = <&dcmi_sleep_pins_a>;

	port {
		dcmi_0: endpoint {
			remote-endpoint = <&ov5640_0>;
			bus-width = <8>;
			hsync-active = <0>;
			vsync-active = <0>;
			pclk-sample = <1>;
			pclk-max-frequency = <77000000>;
		};
	};
};

</nowiki></pre>
<li>增加OV5640节点</li>
修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi文件，在I2C5节点中添加OV5640设备信息，红色字体为增加内容：
<div style="background-color:#F8F8F8;border:1px solid #E5E5E5;font-family: monospace,Courier;">
:&i2c5 {<br>
::  pinctrl-names = "default", "sleep";<br>
::  pinctrl-0 = <&i2c5_pins_a>;<br>
::  ……<br>
<font color="#FF0000">
::  ov5640: camera@3c {
:::		compatible = "ovti,ov5640";
:::		reg = <0x3c>;
:::		clocks = <&clk_ext_camera>;
:::		clock-names = "xclk";
:::		DOVDD-supply = <&v2v8>;
:::		powerdown-gpios = <&gpioa 4 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
:::		reset-gpios = <&gpioa 3 (GPIO_ACTIVE_LOW | GPIO_PUSH_PULL)>;
:::		rotation = <180>;
:::		status = "okay";
:::
::		port {
:::			ov5640_0: endpoint {
:::				remote-endpoint = <&dcmi_0>;
:::				bus-width = <8>;
:::				data-shift = <2>; /* lines 9:2 are used */
:::				hsync-active = <0>;
:::				vsync-active = <0>;
:::				pclk-sample = <1>;
:::				pclk-max-frequency = <77000000>;
:::		  	};
::		};
:	};
</font>
};
</div>
<li>增加2.8V电源和24M时钟</li>

修改arch/arm/dts/stm32mp15xx-fsmp1x.dtsi文件，在根节点最后添加2.8V电源和24M时钟，红色字体为增加内容：

<div style="background-color:#F8F8F8;border:1px solid #E5E5E5;font-family: monospace,Courier;">
:/{<br>
::  memory@c0000000 {
:::  device_type = "memory";
:::  reg = <0xc0000000 0x20000000>;
::  };
:: ……
<font color="#FF0000">
::  v2v8: regulator-2p8v {
:::		compatible = "regulator-fixed";
:::		regulator-name = "v2v8";
:::		regulator-min-microvolt = <2800000>;
:::		regulator-max-microvolt = <2800000>;
:::		regulator-always-on;
:::		regulator-boot-on;
::	};
::	clocks {
:::		clk_ext_camera: clk-ext-camera {
:::			#clock-cells = <0>;
:::			compatible = "fixed-clock";
:::			clock-frequency = <24000000>;
:::		};
::	};

</font>
};
</div>
<li>配置内核</li>

配置内核支持ov5640，并列出主要选项，如下
<pre><nowiki>
linux@ubuntu:$ make menuconfig
Device Drivers  --->
	<*> Multimedia support  --->
		[*]   V4L platform devices  --->
			<*>   STM32 Digital Camera Memory Interface (DCMI) support 
		I2C Encoders, decoders, sensors and other helper chips  --->
			<*> OmniVision OV5640 sensor support
</nowiki></pre>
<li>编译内核及设备树</li>
 linux@ubuntu:$ make -j4 uImage dtbs LOADADDR=0xC2000040
<li>重启测试</li>

将编译好的设备树和内核镜像拷贝到/tftpboot目录下，通过tftp引导内核，系统启动后启动信息中包含如下信息：

[[Image:58-1-4-1.png]] <br>

在屏幕的界面上选择“Camera preview”应用进入摄像头预览程序，启动界面后即可看到摄像头实时采集的图像。

[[Image:58-1-4-2.png]] <br>