SPI LCD as a framebuffer

kekerman
 
Posts: 7
Joined: Fri Jan 13, 2017 9:11 pm

SPI LCD as a framebuffer

Sun May 21, 2017 2:42 pm

I want to be able do display something on the LCD, but only through a framebuffer. I googled a bit and found out that many people done that, but no one posted a step by step solution. I have a display like this one - https://www.youtube.com/watch?v=pax7kA2gCFs and http://www.haoyuelectronics.com/Attachm ... le-A-1.jpg

I am a linux newbie, so hacking kernel is a bit too difficult I think ;) Does anyone know how to acces this lcd by a framebuffer?

Vonger made a post about connecting only http://vonger.cn/?p=8216 yet I don't know why we need to combine mosi and miso to sda. Can't I just connect MOSI to SDA?

noblepepper
 
Posts: 238
Joined: Sat Nov 29, 2014 3:22 pm

Re: SPI LCD as a framebuffer

Mon May 22, 2017 9:04 pm

Nice picture, I don't waste my time watching YouTube videos about tech stuff. A model number and spec sheet would be useful.

IIRC Vonger's blog post is about connecting a non standard display, I would avoid that and use a 3/2.5v 4 wire spi display that uses a controller chip supported by the frame buffer you want to use. They abound on eBay for few $$.

The only framebuffer I found with even a chance of getting in mainstream kernel is fbtft it isn't hard to get working on a system with fully functional spi (vocore 1 works)

The 7628 has a hardware limit on spi transfer size that prevented using a framebuffer or much of anything else the last time I tried. Since then I found this patch that works for using flashrom over spidev. It should work for fbtft but I haven't tried.

Until there is a working dma/spi driver performance will be unimpressive.

Vonger
 
Posts: 558
Joined: Sun Oct 19, 2014 6:00 am

Re: SPI LCD as a framebuffer

Tue May 23, 2017 1:21 am

@kekerman I can only find 3-wires lcd screen, ILI94xx only 3wires :) lucky me, use a resistor I can make it work.
@nobblepepper step by step, we will have dma spi later :)

actually vocore2 spi is much faster, it send one spi package 32 bytes, but vocore send package byte one by one, even it is able to send different length of spi package but time cost on compose the package.

kekerman
 
Posts: 7
Joined: Fri Jan 13, 2017 9:11 pm

Re: SPI LCD as a framebuffer

Tue May 23, 2017 3:07 pm

So I should compile source from http://vocore.io/v2.html with fbtft for my screen driver and it should just work? Anything I write to framebuffer will be sent to the screen, right?

Vonger
 
Posts: 558
Joined: Sun Oct 19, 2014 6:00 am

Re: SPI LCD as a framebuffer

Mon Jun 05, 2017 8:41 am

I will write a tutorial step by step, actually I am newbie to it too.
10K is necessary, convert 4pin spi to 3 pin spi.

kekerman
 
Posts: 7
Joined: Fri Jan 13, 2017 9:11 pm

Re: SPI LCD as a framebuffer

Mon Jun 05, 2017 12:13 pm

Ok, great. Thanks ^^

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