This is a proof of concept for using a small graphical LCD with the ST7565 chipset as a character device in Linux.
So far, the code has been tested on a BeagleBone Black running Debian 7.0 (Wheezy) connected to this LCD:
A fair amount of work has to be done first, before the driver code can be compiled. The community for the BeagleBone Black has made this pretty easy though.
- Prepare an SD card with a Debian image:
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Install a new kernel and kernel headers. You must make sure to choose one that has the kernel headers included; not all of them do.
For example, this has the kernel headers included:
Now, just grab the installer script and run it:
wget http://rcn-ee.net/deb/wheezy-armhf/v3.8.13-bone23/install-me.sh su sh install-me.sh rebootAfter rebooting, run 'uname -r' and the result should be '3.8.13-bone23'.
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Use this script to download, patch and prepare the kernel source for your board. This will not work if you don't have kernel headers available.
https://github.com/gkaindl/beaglebone-ubuntu-scripts/blob/master/bb-get-rcn-kernel-source.sh
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Now you should be able to compile kernel drivers.
make clean make su insmod st7565.koThe command 'dmesg' will print kernel messages and help you debug problems.
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Wire up the LCD. You can change the pin definitions in st7565.c to suit your needs. By default, they are:
#define ST7565_CS GPIO_TO_PIN(1, 13) #define ST7565_RST GPIO_TO_PIN(1, 12) #define ST7565_A0 GPIO_TO_PIN(0, 26) #define ST7565_CLK GPIO_TO_PIN(1, 15) #define ST7565_SI GPIO_TO_PIN(1, 14) -
Finally, print some text on the LCD!
su echo "hi from linux" > /dev/st7565
This driver bit-bangs SPI instead of using the hardware SPI. The reason is that the hardware SPI has a pin conflict with the HDMI output on the BeagleBone Black, and I found it a better compromise to bit-bang rather than disable the HDMI.
You also might notice that at several points above, I used 'su' instead of 'sudo', which is probably considered poor practice. The reason for this is that several of the required steps fail with sudo.