Hardware display backends
Hardware display backends support various displays connected to hardware GPIO e.g. SPI e-ink RPi Hat. These displays are coupled with Linux input driver so that you can get a computer with a keyboard, mouse and display just by connecting display to GPIOs as well as USB keyboard and/or mouse.
In order to start an application with a hardware display backend display:$display_name string has to be passed to the display init function. This is usually done on a commandline by passing the -b option.
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In order to run display backends as a regular user the user has to be in the right groups that is gpio and for SPI displays spi group as well. |
E-ink displays
E-ink displays repaint is slow, especially the large ones, the refresh can take up to a few seconds. In order to make such displays usable with an interactive work e-ink display backends implements asynchronous mode. That means that during the display refresh the areas that were requested to be repainted by the application are merged and once the display is ready the merged area is refreshed on the display. With this even terminal emulator is quite usable on e-ink displays.
E-ink displays that support partial refresh have to do a full refresh once in a while in order to get rid of noise/artifacts/ghosts that is added by doing several partial refreshes in a row. The e-ink display layer keeps track of partial refreshes and schedulles full refresh when needed so that this is transparent to the application.
SPI displays
SPI displays need spidev userspace SPI driver and a few GPIOs for additional signaling. The default RPi GPIO mapping is compatible with WaveShare e-ink display hats.
| Display | GPIO | Display SPI | GPIO |
|---|---|---|---|
Reset |
17 |
MOSI |
10 |
Data/Command |
25 |
MISO |
9 |
Power |
18 |
SCLK |
11 |
Busy |
24 |
CS0 |
8 |
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SPI displays require spidev (userspace SPI interface) driver that is bind to the hardware SPI driver. On RPi this is done by raspi-config where you enable SPI and reboot. After the reboot the /dev/spidev0.0 should be available. |
| Name | Type | Driver IC | Depth | Resolution |
|---|---|---|---|---|
e-ink |
GD7965 aka UC8179c |
1 BPP |
800x480 |
|
e-ink |
SSD1677 |
1 BPP |
480x280 |
|
e-ink |
SSD1680 |
1 BPP |
250x122 |