Get certain TFT LCD working on SPI1

Question

Hi everyone!

I'm very new to raspberrypi and have spent the last couple of weeks learning as much as I can. I have installed the latest version of Raspian and I'm trying to get a 3.5" LCD to work on SPI1 instead of SPI0 (which I need for other components): http://www.uctronics.com/display/uctron ... -pi-b.html

Here is the driver: https://github.com/UCTRONICS/UCTRONICS_LCD35_RPI

I tried to follow this post: viewtopic.php?f=63&t=157618&p=1214626#p1214626

But all I get is a white screen.

Does anyone have some suggestions? Ultimately I will want to use SPI1 as the bus for my primary display for desktop interface/retropi etc

I have been trying to figure this out for a while now and could really use a hand.

Do I have to make any changes to the driver for the screen?

I have it wired up like the following:

SCREEN - PI

5V = PIN2 (5V power)

MOSI = PIN38 (SPI1 MOSI)

MISO = PIN35 (SPI1 MISO)

SCLK= PIN40 (SPI1 SCLK)

GND= PIN6 (Ground)

T_CS= PIN12 (SPI1 CE0)

L_CS= PIN11 (SPI1 CE1)

And also note that I have it working when I just attach using the included header - which obviously connects it to SPI0.

Thanks in advance!

Darren

shabaz · Answer

Hi Darren,

It's going to be tricky, but in theory possible. The way it works is that there is a driver, which may or may not be flexible enough for this. It likely is flexible enough, but I can't say for sure. I bet they are using a standard driver that has been available for a long time, since there are many SPI-controlled small LCD screens for the pi. If it is flexible enough, then there is also a 'device tree' source file that needs modifying and compiling, but I couldn't see the source for it in the github location that you mentioned; it just had the compiled output (.dtb or .dtbo) device tree file. It may be easier to adapt the other device to use SPI1 (or get them both to use SPI0, but that possibly may not be possible due to the data rate that the display consumes).

So, in summary it is feasible, but a lot of work digging around in the code to work it out. The manufacturer of the display is best placed to help since they will have prepared the device tree file. The other possibility is to also ask on the raspberrypi.org forum, because as I understand (I could be wrong) the person who wrote the original driver (which everyone else rips off : ( originally sold his displays by advertising in the forum there in their 'for sale' section.

shabaz · Answer

Hi Darren,

I think the generic one is here:

https://github.com/notro/fbtft-build

There are patches there that pull in files from other folders, and the dts files are there too. I'm guessing though : ( I'm no expert in this. I don't want to point you down a path that could be futile though, so it is best if you can still try to reach out to the manufacturer, get them to supply you a modified driver or dts file that does what you need it to do.