Update 28/12/2014: I have new post 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.

Update 05/12/2014: Noralf 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. 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.

Introduction

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 🙂 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 driver 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.

Adding Support to fbtft

First up I forked the code to my own github account. 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.

Building a custom kernel

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.

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”.

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):-

• Device Drivers —>
  • Input device support —>
    • [*] Touchscreens —>
      •  <*> ADS7846/TSC2046/AD7873 and AD(S)7843 based touchscreens
  • [*] SPI support —>
    • <*> BCM2708 SPI controller driver (SPI0) {changed from M to *, gets around modules blacklist problem}
  • Graphics support —>
    •  Console display driver support —>
      • [*] Framebuffer Console Rotation
    • <*> Support for small TFT LCD display modules —>
      • <*> FB driver for the ILI9481 LCD Controller
      • <*> FB driver for the ILI9486 LCD Controller
      • <*> Module to for adding FBTFT devices

Once you have selected the options about exit the menu and save the changes when prompted.

Now we also need to edit the arch/arm/march-bcm2708/bcm2708.c board config file to replace the spidev for our tontec35 driver. Without making the change it won’t be possible for the fbtft driver to claim the SPI port. While we are editing in this area we will also add the config for the touch screen driver (ads7846).

Fisrt open up the file arch/arm/mach-bcm2708/bcm2708.c and find the section that looks like this:

Then replace it with the following and save changes:

We also need to add some header files to the top of this file of the kernel will fail to build.

 

Ok now its time to build the kernel.

Now you should have a file (fbtft-kernel.tgz) that you can transfer to the RapsberryPi. As I am using Linux and the Pi is also running Linux is simply transfer it using scp. There are many other ways to get the file to your Pi I will let you work it out. But for now here is how I do it:

Once the file has been transferred you need to install it on the Pi. So login to the Pi (either on the console or via ssh). Then perform the following:

Ok almost there. Now we also need to edit /boot/cmdline.txt to tell the kernel to use the new framebuffer for console output. We basically add “fbtft_device.name=tontec35_9486 fbtft_device.rotate=90 fbcon=map:10 fbcon=font:VGA8x8” before the “rootwait” parameter. Note: This should be one line and is probably displayed wrapped in the browser and your text editor.

Example for models with ili9486 displays:

Example for models with ili9481 displays. The key difference is the fbtft_device.name=* part:

Once you have saved the cmdline.txt and exited your editor you also need to edit /boot/config.txt to tell the RPi what kernel to load. Open up the file and look for a line beginning with “kernel=”. If this line does not exist add one somewhere in the file like this (added to the bottom of the file):

Once you have saved the config.txt file you can try out the TFT. Type “sudo reboot” to restart your Pi. When it comes backup you should now see the console output on your TFT.

Note: If you installed the software provided by Tontec you will want to disable/remove it before your reboot. If you don’t then there might be some strange behaviour as the kernel driver and userspace application both try and control the screen. The easiest way to disable it is to comment out the line in “/etc/init.d/lcd” that reads “sudo /home/pi/mzl350i-pi-ext/src/mzl350i”.

Pre-built kernel

I am aware that most people probably won’t want to roll your own kernel out so I have uploaded a copy of my kernel here for your convenience. You can follow the following procedure on your Pi to install it:

Update 04/12/2014: Added a new kernel image. This image now supports both the ili9481 and the ili9486 displays in the same image. It also adds spi-bcm2708 drivers into the kernel instead of being a module. This enables the screen to start up quicker and removes the need to edit the modules blacklist files. See above for details about selecting correct display in cmdline.txt.

Touch Screen

The kernel image described above also includes support for the touch screen. To confirm it works please install the following packages:

You can confirm that the driver is loaded using the dmesg command.

From the above we can see that the touch screen has been added to input0. This will translate to “/dev/input/event0” as a device node. You can confirm that touching the screen generates events using the evtest program.

You can also try the ts_test and ts_calibrate. These use libts and have some basic graphics.

I am yet to try X-Windows. Once I have more information on this I will update the page.

 

Thanks for reading. Feel free to leave comments or questions below.