Difference between revisions of "Framebuffer driver for SH1106"

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Revision as of 05:33, 19 December 2017

If you want to ditch ZPUI and use the ZeroPhone screen from your own code, you might want to use a framebuffer. This is how to compile and install FBTFT drivers for the SH1106 and drive the screen, all using a Raspberry Pi Zero.

Warning: this article describes compiling your own kernel modules. You might not *have* to do that in the future, that is, when Raspberry Pi finally merges the fb_sh1106.c driver. You definitely do not need to compile anything if you're using a SSD1306 screen (the official ZeroPhone screen is SH1106, so if you're using a ZeroPhone you didn't yourself assemble with a SSD1306 screen, you most likely have SH1106.)

If you have the fb_sh1106 driver available (can check with "modinfo fb_sh1106"), skip to the #Loading the driver section.

Full command-line


Preparing for compiling stuff

sudo apt-get update
sudo apt-get dist-upgrade
#If the dist-upgrade command has installed a new kernel, reboot, then continue from the next line
sudo apt-get install git bc raspberrypi-kernel-headers

Getting sources

I wish I could say "apt-get install raspberrypi-kernel-sources", however, they're *still* available only from Github, not from Raspbian repositories.

git clone --depth=1 https://github.com/raspberrypi/linux
cd linux/

Applying the SH1106 driver initial commit

This instruction was tested on: 4.9.59+ kernel

The commit that added the driver was made later than the 4.9.59 release, which is what the article is written for. You might not need it if you're running later versions of Raspbian, Raspbian Testing or other Raspberry Pi OSes.

Here's the commit in question, you can wget it with:

wget https://github.com/torvalds/linux/commit/079306e979d7f8bb1081ce43c7fc1fa8c1d45d55.patch

Apply it with:

git apply 079306e979d7f8bb1081ce43c7fc1fa8c1d45d55.patch

However, it's not done yet. FBTFT has changed between the 4.9.59+ release and when the commit was created. Specifically, the set_gamma function signature has changed. Run this command-line to patch it:

sed 's/u32 \*curves/unsigned long *curves/' drivers/staging/fbtft/fb_sh1106.c

Preparing the kernel module compilation

In order to build the kernel modules, we need to get .config and Module.symvers files.

cp /usr/src/linux-headers-4.9.59+/Module.symvers .
cp /usr/src/linux-headers-4.9.59+/.config .

Compiling and installing the driver

make oldconfig

Press 'm' when asked on what to do with the SH1106 driver and any FBTFT-related drivers. Press 'n' or 'm' (whatever you want) for any unrelated modules that might pop up.

make modules_prepare
make M=drivers/staging/fbtft

If nothing has failed by this point, the driver should be ready! Now, let's copy it into the module directory:

sudo cp drivers/staging/fbtft/*.ko /lib/modules/4.9.59+/kernel/drivers/staging/fbtft/

We also need to register it with the system, so that modprobe knows about it:

sudo depmod -a

Loading the driver

If you're doing this on ZeroPhone, do know that ZPUI won't be accessible to you after loading the driver (and until you reboot, unless somebody writes instructions on unbinding devices). Thus, you might want to enable the USB port before doing this, for example.

Before loading, stop ZPUI:

sudo service zpui stop

Load the module:

sudo modprobe fbtft_device custom name=fb_sh1106 gpios=reset:5,dc:6 speed=32000000

At this moment, the screen should flicker or something (it might not flicker, though). To see if anything has failed along the way (the module won't always fail to load upon error):

dmesg|tail -n30

Testing if it works

  1. You should get a new framebuffer device - likely, /dev/fb1
  2. With "sudo con2fbmap 1 1", you should get a Linux console on the screen
  3. You can output images to the screen with "fbi":
sudo fbi -T 1 -d /dev/fb1 -a /home/pi/ZPUI/splash.png