DSI interface general information

[TJM]

Hello.  I've placed this here as it's the closest location for LCD display information I can find.

I've picked up an LCD display hoping to drive it and display some sensor information.  The display is 400x1280 and 7.9 inches wide.  It came with an HDMI to DSI converter board and this all works nicely but I'm lacking some basic information, I think.  First, there are a lot of these things, as a unit, that require an HDMI input then convert to DSI.  I'm not finding anything that allows feeding the LCD-DSI interface directly.  I'll put the first two questions here:

1. Why is the HDMI-DSI interface so prevalent?  I understand the possible usage as a secondary display and the HDMI input makes that easy but my thinking is if I want to drive the DSI LCD directly, why would I want to feed it the HDMI signal instead of the DSI signals directly through an IC, a driver, or both?

2. Are there DSI boards and drivers in any combination other than the few ST dev boards with DSI built in that simplify the driving of these LCD-DSI panels?  An ideal situation would be to choose an MCU board of my choice, connect it to the elusive DSI IC/Driver, attach the DSI LCD panel using the appropriate cable (10 to 40pin FFC is common) then use whatever is available as a driver to produce the display.

Any information would be useful, including a 'this is not possible' or 'this is not a good direction to go' reply, but a suggestions to find more pertinent information would be nice.  It doesn't appear there are IC's or dev boards available to allow this to be simplified but the HDMI-DSI adapters appear to have a MPU on board that drives the conversion in firmware instead of using a dedicated DSI IC.  It's also odd that even with some part numbers it's difficult to find datasheets with all the necessary information to drive these DSI-LCDs.

Thanks,

TJM 

[Tesla DeLorean]

>>Why is the HDMI-DSI interface so prevalent?  

Because people have HDMI screens, televisions, and set-top boxes and FireSticks that work with them.

DSI is designed for board-to-board level connectivity within designs that are integrated and lack flexibility.

There are a bunch of drivers for assorted ST boards in the Drivers/BSP and Drivers/BSP/Component directories of the Cube packages.

There are all manner of DSI to RGB, DSI to VGA type ICs out there, not particularly well suited to makers/hackers due to the amount of wires involved and  the bandwidth/frequency of such things.

Most of the ICs are complex and specialized, covered by licensing and patents, with documentation / materials provided under NDA, so serious commercial businesses over makers and tire-kickers.

https://github.com/STMicroelectronics/stm32-otm8009a/blob/d8caa51709b6beabc28ff40268c513c74bad11f1/otm8009a.c

https://github.com/STMicroelectronics/32f769idiscovery-bsp/blob/adccc7dc7a84483175f5e340e6cb69e97196a6f1/stm32f769i_discovery_lcd.c

[Tesla DeLorean]

https://github.com/STMicroelectronics/stm32-adv7533/blob/d772ea912c4f1250491adf7f4a4b1646f3c7c012/adv7533.c

ADV7533  https://www.analog.com/media/en/technical-documentation/data-sheets/adv7533.pdf 

The displays support DSI directly have a controller to panel interface, and flex-circuit connectivity, out-of-the-box and don't need any intermediary conversion or additional ICs.  See OTM8009A   https://www.orientdisplay.com/pdf/OTM8009A.pdf

[Tesla DeLorean]

RGB to VGA DAC

ADV7125  https://www.analog.com/en/products/adv7125.html

GM7123C / ADV7123  https://www.analog.com/en/products/adv7123.html

https://electronics.stackexchange.com/questions/572468/two-pins-on-adv7123-video-dac-is-tied-to-ground

[TJM]

Once, again, thanks for the info and links.  As I stated in the 'other' thread, I think I'm in over my head on this one.

I see the advantage of using the HDMI input to these DSI LCDs to use for secondary displays, or even a main display since these things come in such a variety of sizes.  But for the phones or automotive displays it appears, like you said, they are using some very proprietary chips to drive the DSI displays directly.  I have an ST F469 Disc kit that I'll dig into a bit more but even this thing has oddball one-off connectors between the board and display so it would be a big deal to replace the LCD on the board with mine.  Anyway, browsing quickly through the OTM8009A datasheet it appears this could power a generic interface board capable of using several types of video inputs and output to a MIPI-DSI display.  I don't find such a board at this time.  Thanks for the info in both threads.  Have a coffee.

Thanks,

TJM

[Tesla DeLorean]

Yes the panel from the F469 likely a catch-of-the-day from a phone project that may not exist any more.

They connectorized this display for the F769-DISCO and the EVAL board. There was going to be an Arduino board using it too, but that stalled out. STAR OTTO ??

The reason to connectorize is to allow flexibility in implementation, if you own the interface you can rework a daughter card with a display rather than have to reengineer your own PCB with BGA chips every time you have to switch display vendor.

HDMI has a licensing cost, some generic MICTOR connector does not. Still having costs, and be rated for 200+ MHz signalling and clocks..

There are probably a handful of flex-connector options too, but there it's about where the cables exit and fold, and that the panel has been specified by someone moving large volumes, and perhaps less economic to get customized to your own requirements. Or re-engineering at Vendor#2

https://www.elektormagazine.com/news/stmicroelectronics-joins-the-arduino-community

https://community.st.com/t5/stm32-mcus-products/what-happened-to-arduino-star-otto/td-p/475778