Linux/DS90UB941AS-Q1: 941-948,sometimes there is no display on screen

user5381542

Part Number: DS90UB941AS-Q1
Other Parts Discussed in Thread: ALP

Tool/software: Linux

my board is imx8qxp,data pata:mipi dsi --> ssd2858-->941-->948-->lcd(1920x720);sometimes there is no display on screen;

when no display,i dump 941-948 Regs,the key regs:941:register[0x0c],data[0x67], register[0x5f],data[0x6e],it seems normal;948：the LOCK PIN is high,PASS pin is low；

so，there are other REGISTES which can tell us the input mipi signal to 941 is normal？or how can i debug this issues?

over 6 years ago

0 Sally Cheung95 over 6 years ago

TI__Expert 5480 points

Hi Carrick,

Let's first try to start at each device and see if there are any issues and then we can work our way up. Can you please try enabling the PATGEN for both the SER and DES individually and see if you are able to see the display. In the ALP, instead of programming it yourself, you may use the pattern generator tab for ease. If not, please follow the description on using PATGEN in the D/S.

Thanks,
Sally

0 Sally Cheung95 over 6 years ago in reply to Sally Cheung95

TI__Expert 5480 points

Hi Carrick,

Any other follow up questions?

Thanks,
Sally

0 user5381542 over 6 years ago in reply to Sally Cheung95

Prodigy 170 points

i'm trying wait for moment

0 user5381542 over 6 years ago in reply to Sally Cheung95

Prodigy 170 points

after restart system,when enabling the PATGEN for 941 or 948(write Reg:0x64 Val:0x15),i can see Color Bars on screen;
the question is :sometimes there is no display on screen,most times,the display is normal;

0 Steven(Shenzhen) Shi over 6 years ago in reply to user5381542

TI__Mastermind 30515 points

two comments:
1. you should check this issue from system level why the display panel has issue sometime. 941/948 just is one bridge to transmit the DSI I/f video input to LVDS video output, but the panel display includes other factors which could cause this issue, such as power supply, cable quality, etc., also you can check 948's lock status, is it normal when issue is reported?
2. if pattern test (with internal timing) has same result as the video transmission from i.MX8, I think this issue should not be 941/948 issue.

Steven

0 user5381542 over 6 years ago in reply to Steven(Shenzhen) Shi

Prodigy 170 points

thank you for reply;

1,,it seems normal when issue is reported;948：the LOCK PIN is high,PASS pin is low；we have checked the most factors;

2,when issue is reported,do we judge the input dsi video signals is normal from 941/948 Regs?

0 Steven(Shenzhen) Shi over 6 years ago in reply to user5381542

TI__Mastermind 30515 points

1. pass pin should be high, you can check 948 error reg., also you should measure LOCK pin with scope!
2. you can check 941's reg. to check whether it has DSI error detection.

Steven

0 user5381542 over 6 years ago in reply to Steven(Shenzhen) Shi

Prodigy 170 points

1,pass pin should be high? are your sure?in normal display,pass pin always low;

0 Steven(Shenzhen) Shi over 6 years ago in reply to user5381542

TI__Mastermind 30515 points

pls check d/s page9 on PASS pin description. For your issue, I recommend you debug it step by step to find out the root cause, you can use the pattern test as well.

www.ti.com/.../ds90ub948-q1.pdf

Steven

0 user5381542 over 6 years ago in reply to Steven(Shenzhen) Shi

Prodigy 170 points

in 948 pdf:

BIST mode status output pin (BISTEN = 1)
PASS = 1: No error detected
PASS = 0: Error detected

it describes in BIST mode,the PASS PIN must be HIGH; in normal display,is it also HIGH?

0 Steven(Shenzhen) Shi over 6 years ago in reply to user5381542

TI__Mastermind 30515 points

pls check the d/s carefully.

Normal mode status output pin (BISTEN = 0)
PASS = 1: No fault detected on input display timing
PASS = 0: Indicates an error condition or corruption in display timing. Fault condition
occurs:
1. DE length value mismatch measured once in succession
2. VSync length value mismatch measured twice in succession
BIST mode status output pin (BISTEN = 1)
PASS = 1: No error detected
PASS = 0: Error detected

Steven

Interface

Interface forum

Linux/DS90UB941AS-Q1: 941-948,sometimes there is no display on screen