{"id":14,"date":"2014-11-30T16:44:11","date_gmt":"2014-11-30T16:44:11","guid":{"rendered":"http:\/\/cooljc.me.uk\/?page_id=14"},"modified":"2015-11-02T12:04:59","modified_gmt":"2015-11-02T12:04:59","slug":"tontec-3-5-tft","status":"publish","type":"page","link":"https:\/\/cooljc.me.uk\/?page_id=14","title":{"rendered":"Tontec 3.5″ TFT"},"content":{"rendered":"

\"IMG_20141129_105125\"<\/a><\/p>\n

Update 28\/12\/2014<\/strong>: I have new post<\/a> that should now be used for setting up the display and touch screen. It uses the pre-build kernel from Notro rather than my kernel as it will be kept more up to date.<\/p>\n

Update 05\/12\/2014<\/strong>:\u00a0Noralf has now included my patches in his master branch of fbtft driver. He will release a new kernel including this driver soon. For more information visit his wiki here<\/a>. Of course you can still follow the guide below if you wish to get roll your own kernel. It is also useful as a reference for getting the touch screen working.<\/p>\n

Introduction<\/strong><\/p>\n

I received this device as a birthday present last weekend. I was keen to get it going so I downloaded the 35screen.zip off the manufactures web site and began running through the user manual. After about 20 minutes I had the screen working \ud83d\ude42 I soon realized that the software (“driver”) was quite lame and ran completely in userland (no place for a hardware driver to run). So I took to google and started searching for spi based LCD frame buffer drivers and came across the excellent fbtft<\/a>\u00a0driver by Notro. Reading through the documents in the wiki I soon discovered that the Tontec 3.5″ device was not supported by this driver. So no stranger to some kernel hacking I decided to add support for it.<\/p>\n

Adding Support to fbtft<\/strong><\/p>\n

First up I forked the code to my own github account<\/a>. I then set about trying to locate some datasheets for the screen. This proved very tricky so I gave up and decided to reverse engineer the lame driver that came with it. Browsing the code I came across some references to ili9481, great there might be some light at the end of the tunnel as fbtft already had support for this device. After some initial tests I found it was not as simple as using the existing ili9481 driver. The main differences were the gpio control pins, the device register width, SPI mode and the initial state of the backlight. For the gpio assignments this was taken from the user manual. The other items were worked out from the tontec source code.<\/p>\n

Building a custom kernel<\/strong><\/p>\n

Before I begin let me explain my setup. I will be using a relatively low end laptop running Ubuntu Linux. Building the kernel (or any other large code base) on the Pi is insane as it would take an age and when your hacking you want to get testing changes as quickly as possible. So all steps below will be run on the PC unless stated otherwise.<\/p>\n

# Create some directories\r\n\r\n# Start in the users home directory\r\ncd $HOME\r\n\r\n# Create a directory to keep tools and sources in\r\nmkdir touch\r\n\r\n# change into touch directory\r\ncd touch\r\n\r\n# create a fake root fs used for zipping up kernel and models for transfer to Pi\r\nmkdir -p rootfs\/{boot,lib}\r\n\r\n# Clone the raspberry pi kernel source\r\ngit clone https:\/\/github.com\/raspberrypi\/linux.git --depth 1\r\n\r\n# Clone the raspberry pi tools. This includes the cross compiler and mkimage scripts.\r\ngit clone https:\/\/github.com\/raspberrypi\/tools.git --depth 1\r\n\r\n# Clone fbtft into the linux\/drivers\/video directory\r\ncd linux\/drivers\/video\r\ngit clone https:\/\/github.com\/notro\/fbtft.git\r\n\r\n# patch the kernel files to include the new drivers (from fbtft wiki)\r\necho \"obj-y += fbtft\/\" >> Makefile\r\nsed -i 's\/endmenu\/source \"drivers\\\/video\\\/fbtft\\\/Kconfig\"\\n\\nendmenu\/' Kconfig\r\n\r\n# we need to create a symbolic link to the fbtft.h file so it can be included in bcm2708.c\r\ncd ..\/..\/include\/linux\/spi\r\nln -s ..\/..\/..\/drivers\/video\/fbtft\/fbtft.h .\r\n\r\n# change back to the linux source top directory\r\ncd ..\/..\/..\/\r\n\r\n# Setup some environment variables required for cross compiling the kernel\r\n# 1) set the target architecture\r\nexport ARCH=arm\r\n\r\n# 2) add the path to the cross compiler to your shells path\r\n#    I am using the x86_64 version of the compiler.\r\nexport PATH=$HOME\/touch\/tools\/arm-bcm2708\/gcc-linaro-arm-linux-gnueabihf-raspbian-x64\/bin:$PATH\r\n\r\n# 3) set the toolchain prefix\r\nexport CROSS_COMPILE=arm-linux-gnueabihf-\r\n\r\n# 4) set the modules install path to our fake root\r\nexport INSTALL_MOD_PATH=$HOME\/touch\/rootfs\r\n\r\n# 5) prepare for building by using the default Raspberry Pi config\r\nmake bcmrpi_defconfig<\/pre>\n
Before beginning the build we need to enable the fbtft drivers (while we at we should also enable the touch screen driver). To enable the drivers we need to run “make menuconfig”.<\/p>\n
# run kernel menu config\r\nmake menuconfig<\/pre>\n
Using the menu is quite simple. Cursor up, down, left, right, enter and spacebar are the only keys you need to use. So once it is up and running navigate to the following sections (*=built in, m=module, select using spacebar):-<\/p>\n