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Controlling OmapL138 EVM backlight

Jack L
Prodigy 50 points
Other Parts Discussed in Thread: OMAPL138, OMAP-L138

I am using the OmapL138 evaluation board and need to control the LCD backlight (userspace slider)

I built the 03.22 kernel using instructions here http://processors.wiki.ti.com/index.php/LCD_brightness_control_on_da850/omap-l138

But there is no brightness change when I set the brightness value like so.

echo 10 >  /sys/class/backlight/pwm-backlight/brightness

What would I need to do to get the LCD brightness to work?

Thanks in advance

  • 0
    TI__Guru* 81335 points

    Hi Jack,

    Note:

    Please check the board revision of Logic PD. The older revision uses eCAP whereas the latest revisions uses the eHRPWM peripheral.

    Step to build: (Please ensure to have the right image to test)

    All your commands looks OK. Please try with following kernel version.

    1. Please download the PSP(Kernel source) from AM18x from below link.

    http://processors.wiki.ti.com/index.php/DaVinci_(ARM9)_PSP_Releases#AM18x

    2. Enable the PWM supports in Menuconfig

     Device Drivers ---> 
     <*> PWM Support ---> 
     <*> Davinci eHRPWM support 
     Device Drivers ---> 
     <*> PWM Support ---> 
     <*> eCAP PWM support  
    3. Disable the Framebuffer & SPI controller support in Menuconfig as below
     Device Drivers ---> Graphics support ---> 
     <*> Support for frame buffer devices ---> 
     < > DA8xx/OMAP-L1xx Framebuffer support 
     Device Drivers ---> [*]SPI support ---> 
     < > Texas Instruments DaVinci/DA8x/OMAP-L/AM18x SoC SPI controller 
    4. Build the kernel.
    Testing the PWM with built kernel: (Use the correct instance number - Refer schematics)
    1. Please follow the below wiki link to control the PWM using eHRPWM. (The valid instance should be 0 to 1)
    http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide#eHRPWM_2
    2. Please follow the below wiki link to control the PWM using eCAP. (The valid instance should be 0 to 2)
    http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide#eCAP_2
    3. To verify, probe the eHRPWM / eCAP pin's.
    

    Thanks.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                 	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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						in reply to Raja
					
									
    
	
    
	                                    
                      
    
                        
                          Prodigy
                        50 points
                      
    
                          
                   		
		
    
					
    Thanks Rajasekaran .
    

    I was able to modify the brightness using eCAP on the LogicPD. And using eHRPWM on a custom board. 
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    

	            
                	
	
    
				
		                
                
                
                
                
                
                
        		
		
				
    
			
		
    
		
		 
		
		
     
    
	
    

    
			
    
			
    
		
    

		
    
	
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