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Zhou JianQiang
Zhou JianQiang
Senior
March 18, 2025
Question

Why DSI clock can't set to more than 500M in STM32H747?

  • March 18, 2025
  • 5 replies
  • 3777 views

Hi 
When I try to set DSI clock more than 500M, the STM32cubemx will display an error message "dsi clock source frequency must be =< 62MHz" as below. But it said STM32H747 DSI clcok can reach 1Ghz in datasheet.

I use 25Mhz HSE and attach STM32cubemx project for reference.

ZhouJianQiang_0-1742263034135.png

 

5 replies

Tesla DeLorean
Tesla DeLorean
Guru
March 18, 2025

Because it's the data across multiple lanes that can get to 1 Gbps

2-Lanes, clocking at 500 MHz each, the DSI clock on the wire is 250 MHz, with data lanes clocking on BOTH edges

The 62 MHz is the pixel clock, for a 16 or 24-bit load, the LTDC delivers words to the DSI, the DSI moves it a bit/lane over the wire.

16 x 62 = 992 bps

I suspect 16 x 62.5 = 1000 bps is the functional limit, or close too it.

The 24-bit colour depth the maximum pixel clock is closer to 41.67 MHz

If you don't like the limits the auto-gen tools apply, stop using them, and use your interpretation of the reference manual and the peripheral mechanics.

https://www.st.com/resource/en/application_note/an4860-introduction-to-dsi-host-on-stm32-mcus-and-mpus-stmicroelectronics.pdf#page=75

https://www.st.com/resource/en/product_training/STM32L4Plus_Peripheral_DSIHOST.pdf

 

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Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 18, 2025

Hi Tesla:

Thank you for your reply.

>Because it's the data across multiple lanes that can get to 1 Gbps

-->but as showing datasheet DS12930(https://www.st.com/content/ccc/resource/technical/document/datasheet/group3/99/a2/f9/3c/27/bc/48/a8/DM00602212/files/DM00602212.pdf/jcr:content/translations/en.DM00602212.pdf), per lane speed can reach 1 Gbps, not multiple lanes.

ZhouJianQiang_0-1742266197381.png

>I suspect 16 x 62.5 = 1000 bps is the functional limit, or close too it.

-->I think it would be better if it was officially confirmed, so let's wait for ST's answer.

>If you don't like the limits the auto-gen tools apply, stop using them, and use your interpretation of the reference manual and the peripheral mechanics.

-->The cubemx can save many time when starting a new project, I am just confused with this limitation.

 

 

TDK
TDK
Super User
March 18, 2025

This is the input clock to the DSI, not the speed of the output which is much higher.

@Tesla DeLorean explains it nicely here:

STM32H7 MIPI DSI maximum clock speed? - STMicroelectronics Community

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Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 18, 2025

Hi TDK:

It says 1 Ghz max here, so I think it still has something wrong here.

ZhouJianQiang_0-1742268094119.png

And in thread you mention, the VCO 2000 is red, but now it is't

ZhouJianQiang_1-1742268311461.png

 

Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 19, 2025

Hi @mƎALLEm :

Can you help confirm this question?

mƎALLEm
mƎALLEm
Technical Moderator
March 19, 2025

It will be handled by CubeMx team.

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.
Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 21, 2025

Hi @mƎALLEm :

Any update?

Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 24, 2025

Hi @Souhaib MAZHOUD :

Can you help confirm this question?

S
Souhaib MAZHOUD
Technical Moderator
March 25, 2025

Hello @Zhou JianQiang 


This issue has been raised to the concerned team for review (Internal ticket number: 206060). I will get back to you as soon as I have any updates.

KR,

Souhaib

To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
Zhou JianQiang
Zhou JianQiangAuthor
Senior
March 28, 2025

Hi @Souhaib MAZHOUD :

Do you have any update?

TDK
TDK
Super User
March 28, 2025

Expect it to take a few weeks at least.

Position yourself so that you are not dependent on fast updates to CubeMX but rather are self-sufficient to ensure success. Look at the release schedule for the past few builds. Expect that it will take at least this much time.

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