lpcware

[SOLVED] LPC1788 LCD display noise issue

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by sgiorgetti on Wed Apr 09 23:59:13 MST 2014
Hello everybody,
we're facing an annoying issue on 30% of production boards and as of today I wasn't able to find any firmware solution to this, even following every post found in this board about LCD and SDRAM initialization procedures.

On affected boards, the LCD shows a lot of pixel noise, as shown in following photo:
[img]http://www.lpcware.com/system/files/TFT%20Noise%20-%20details.jpg[/img]

I am not yet able to determine if this is a LCD or SDRAM peripheral issue, anyway I've found that applying a mechanical pressure on chip, the display changes and it shows the secondary buffer content.
[img]http://www.lpcware.com/system/files/TFT%20Noise%20-%20mechanic%20action.jpg[/img]

In previous picture you can see that the active buffer (flags page) disappears and the secondary buffer (black background with some texts) reappears.
This is exactly the last content of the active buffer, as the previous shown page is
[img]http://www.lpcware.com/system/files/TFT%20Noise%20-%20previuos%20active%20buffer.jpg[/img]

I'm using a custom middleware graphic library, but I don't think that it's a library problem.
The LCD video RAM is managed as a simple double buffer that's stored into two SDRAM sections:

#define C_GLCD_H_SIZE           480
#define C_GLCD_V_SIZE           272
#defineLCD_BPP2/**< LCD byte-per-pixel */


/** Video memory base address */
#define GLCD_BUFFER_BASE0xA0000000/* Uses external SDRAM on DYCS0 */
/** Single buffer dimension [byte] */
#define GLCD_BUFFER_SIZE(C_GLCD_H_SIZE*C_GLCD_V_SIZE*LCD_BPP)

Buffer #1 @ GLCD_BUFFER_BASE
Buffer #1 @ GLCD_BUFFER_BASE+GLCD_BUFFER_SIZE



I'm investigating about:
[list]
  [*]hardware issues (fact: the changes caused by pressure are strange)
[*] LPC peripheral initialization issues (fact: playing with both LCD and SDRAM parameters I can either totally block the application or have no effect at all)
[*] ???
[/list]

I'd really appreciate any possible hint about this problem.
Thank you very much

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