将7寸、1920*1200的高分辨率屏跟CMIO参考板连接

内容介绍

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这个项目先是分享在Hackaday上：7" LCD for Raspberry Pi CM4 CMIO，并在Github上开源出来，搭配树莓派CM4的CMIO板子，由于CM4的DSI接口（22Pin/0.5mm间距）和7寸屏的MIPI接口（31pin/0.3mm间距）线序不同，所以作者做了一个转接板，除了实现线序的调整外，还增加了针对LCD的Reset信号以及1.8V的供电电压 - 如果你直接使用CM4模块，可以从CM4模块中直接获得1.8V的直流电压，而CMIO上无法通过FPC软线提供1.8V直流电压，所以作者在转接板上加了一个3.3V转1.8V的LDO。

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用的显示屏同样也是JDI LT070ME05000 LCD panel，这是一款用在2013年的Google Nexus II上的高分辨率屏，显示效果非常好，比较适合制作便携式的计算机（淘宝上有卖，一百块钱搞定，不过不适合设计大批量的新产品）。

Overview

JDI LT070ME05000 is 7" 1200x1920 4-lane DSI IPS display used in Asus/Google Nexus 7 2013 tablet. To use it, 4-lane DSI interface is required, so it can be used with Raspberry Pi Compute Modules 3 and 4. Some suppliers have these displays available from ~$US20 shipped. There is a driver for this panel in a mainline already included, so we only need to compile/install it and make device tree overlay

Software installation

We need build rpi-5.10.y branch with LT070ME05000 module enabled. This is well documented at Raspberry Pi help pages here and here

sudo apt install git bc bison flex libssl-dev make
sudo apt install libncurses5-dev
git clone --depth=1 --branch rpi-5.10.y https://github.com/raspberrypi/linux
cd linux
KERNEL=kernel7l
make bcm2711_defconfig
make menuconfig

Navigate to Device Drivers/Graphics support/Display panel, check JDI LT070ME05000 panel and save

Now we need to build and install kernel:

make -j4 zImage modules dtbs
sudo make modules_install
sudo cp arch/arm/boot/dts/*.dtb /boot/
sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/overlays/
sudo cp arch/arm/boot/dts/overlays/README /boot/overlays/
sudo cp arch/arm/boot/zImage /boot/$KERNEL.img

Device Tree Source can be modified to assign another GPIO numbers, then compiled and copied to boot partition:

sudo dtc -@ -I dts -O dtb -o vc4-kms-dsi-lt070me05000.dtbo vc4-kms-dsi-lt070me05000-overlay.dts
sudo cp vc4-kms-dsi-lt070me05000.dtbo /boot/overlays/

Then edit /boot/config.txt to add:

lcd_ignore=1
dtoverlay=vc4-kms-v3d
dtoverlay=vc4-kms-dsi-lt070me05000

and reboot

After reboot screen should we working and have portrait orientation. To adjust, use Main Menu/Preferences/Screen configuration utility

LCD pins defaults to:

Reset - GPIO17
Enable - GPIO4
DCDC Enable - GPIO5

Default pins can be changed, for example:

lcd_ignore=1
dtoverlay=vc4-kms-v3d
dtoverlay=vc4-kms-dsi-lt070me05000,reset=5,enable=17,dcdc-en=4

Hardware

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Important notes:

This schematics comes with no warranties, use at your own risk
Verify pin 1 location for your application: two FPC connectors facing each other would have first pin at opposite side
3V3 LDO gets hot. According to datasheet, VDD and VDDp can actually be powered from 3.0-5.0V
i2c part for TP is not tested
LCD_RST MUST be 1.8V with sufficient current, ie resistive divider 3.3->1.8 is likely not to work. If using with RPi CM3, LCD_RST can be directly driven by 1.8 powered GPIO bank

Github资源链接：