101 lines
2.8 KiB
Markdown
101 lines
2.8 KiB
Markdown
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How i installed the 3.5" (A) type of screen on RaspberryOS Bookworm (Debian 12)
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Update: I've tested Bullseye (Debian 11) and it works, but [rotation was not working](#rotation)
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!!! abstract "Disclaimer"
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This is based on my own experience, and it's provided for general information
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and does not constitute as advice of any kind.
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## Initial install
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This screens connect to the [GPIO](https://en.wikipedia.org/wiki/General-purpose_input/output)
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they were usually installed via repositories named LCD-show ([1](https://github.com/waveshare/LCD-show), [2](https://github.com/goodtft/LCD-show)),
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however in the bookworm release there is a simpler solution
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```sh
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sudo nano /boot/firmware/config.txt
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```
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at the bottom add:
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```
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dtoverlay=piscreen,drm
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```
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???+ info
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in this context drm stands for [Direct Rendering Manager](https://en.wikipedia.org/wiki/Direct_Rendering_Manager)
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I had to comment out (add # at the start) vc4 or it would boot into a blackscreen
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```
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#dtoverlay=vc4-kms-v3d
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```
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Close the nano editor using `ctrl`+`x` (exit), then `y` for yes (save).
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```sh
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sudo reboot
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```
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## Wrong colors or graphical corruption
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Some screens will not behave correctly and/or display wrong colors,
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this usually due to the wrong [SPI](https://en.wikipedia.org/wiki/Serial_Peripheral_Interface) speed
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In my case the maximum i could achieve is 22.22Mhz
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```
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dtoverlay=piscreen,drm,speed=22222222
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```
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??? info "About speed"
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As you may predict speed has a big impact in usability as it dictates how often the display will refresh
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If i understand the [involved drivers](https://github.com/torvalds/linux/blob/65d287c7eb1d14e0f4d56f19cec30d97fc7e8f66/drivers/spi/spi-bcm2835.c#L1068)
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correctly, the spi speed is calculated as:
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`core_clock / core_divisor`
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The divisor must be a multiple of 2, that ranges between 2 and 65536
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Core clock in the case of Pi 3 would be 400mhz
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So even if you can enter any number, it will be approximated to a value from that formula
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That's why i used 22.222.222 (400 / 18)
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reboot to test any changes.
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## Rotation
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You can rotate the screen adding a rotate line with the degrees [0, 90, 180, 270]
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```
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dtoverlay=piscreen,drm,rotate=180
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```
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Screen rotation will require adjusting the touch matrix see [Touch issues](../../Troubleshooting/Touch_issues/)
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!!! bug
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Raspberry linux Kernel v6.1.77 has a bug in the dtb and rotate doesn't work
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The fix has been merged in linux v6.6
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you can copy the dtb from the new kernel into the old one if needed
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## Console
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To make the console work:
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```sh
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sudo nano /boot/firmware/cmdline.txt
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```
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add at the start or end:
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```
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fbcon=map:11
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```
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!!! warning "Important"
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Do not add newlines to the file, it must be 1 line with the options separated by spaces
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