DSI + LTDC frequency ratio.

[af.bulychev9]

I have display with controller ILI9881C, which controlled via mipi-dsi.

I want to use 800x800x24bit mode. How to understand what's the point to use dsi txclkex and dsi line byte frequency? and how it is correlate with ltdc frequency? in display controller dataheet i have the next description for frame rate

how can i calculate pixel timings for Horizontal Back Porch and Horizontal Front Porch? is it must be based on ltdc frequency?

[Tesla DeLorean]

The line and frame totals drive the​ pixel clock. The rate of data out of the LTDC has to be matched to the lanes and bits going over the DSI based on your colour depth and pixel clock.

​

Write a "fitter" to get parity in the rates based on the limited clock multipler/divider options. Adjust porches to accommodate within specs of display.​

[af.bulychev9]

Just for clarification, must i use LTDC frequency for bitrate ?

in my case - 24 bit on 108 MHz will equals 4.5 Mb/s , right?

[Tesla DeLorean]

The pixel clock for the example there would be 76.2 MHz. with 1.83 Gbps on the DSI

Problem here is going to be you only have 2 lanes, not 4

Is your SDRAM memory interface 16 or 32-bit wide?

Are you doing video play back? What is the hard frame rate for that?

[af.bulychev9]

@Community member​ 

Why a 720p @ 30Hz in example i do not know. Controller have 800 width

I am experimenting with the next values

FrameRate = 30

PixelFormat = 24

LineN = 2

VACT = 800

VSA = 40

VBP = 100

VFP = 100

HACT = 800

HSA = 40

HFP = 247

HBP = 248

BRbps = 500000000

And calculated

UI = 2e-09

FPS = 30.010563718428887

tHFPCalc=5.928000000000001 us

tHSA + tHBP =6.912000000000001 us