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docs: 35 gpio update

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alfrix 2024-03-12 17:01:52 -03:00
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34
docs/Hardware/GPIO_35.md
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How i installed the 3.5" (A) type of screen on RaspberryOS Bookworm (Debian 12)
Update: I've tested Bullseye (Debian 11) and it works, but [rotation was not working](#rotation)
![preview](../img/hardware/rpi35a.jpg)
!!! abstract "Disclaimer"
@ -41,27 +43,45 @@ sudo reboot
Some screens will not behave correctly and/or display wrong colors,
this usually due to the wrong [SPI](https://en.wikipedia.org/wiki/Serial_Peripheral_Interface) speed
In my case the maximum i could achieve is 22.22Mhz (400mhz core / 18)
In my case the maximum i could achieve is 22.22Mhz
```
dtoverlay=piscreen,drm,speed=22222222
```
As you may predict speed has a big impact in usability as it dictates how often the display will refresh
??? info "About speed"
As you may predict speed has a big impact in usability as it dictates how often the display will refresh
If i understand the [involved drivers](https://github.com/torvalds/linux/blob/65d287c7eb1d14e0f4d56f19cec30d97fc7e8f66/drivers/spi/spi-bcm2835.c#L1068)
correctly, the spi speed is calculated as:
`core_clock / core_divisor`
The divisor must be a multiple of 2, that ranges between 2 and 65536
Core clock in the case of Pi 3 would be 400mhz
So even if you can enter any number, it will be approximated to a value from that formula
That's why i used 22.222.222 (400 / 18)
reboot to test any changes.
## Rotation
!!! bug
The current Rpi Kernel v6.1.77 has a bug in the dtb and rotate doesn't work, fix has been merged in v6.6
you can copy the dtb from the new kernel into the old one if needed
You can rotate the screen adding a rotate line with the degrees [0, 90, 180, 270]
```
dtoverlay=piscreen,drm,rotate=180
```
Screen rotation will require adjusting the touch matrix see [Touch issues](../../Troubleshooting/Touch_issues/)
!!! bug
Raspberry linux Kernel v6.1.77 has a bug in the dtb and rotate doesn't work
The fix has been merged in linux v6.6
you can copy the dtb from the new kernel into the old one if needed
## Console
To make the console work: