Backlight HAL driver or how to control backlight of the VU7+

[joerg]

As I stated already in an other thread I made the driver to control backlight with pwm (pin 33).
The driver need to be copied to the folder system/lib/hw/ and after reboot it should do his job.
The driver loads the kernel modules for pwm automatically, so pwm-meson.ko and pwm-ctrl.ko must be present, what they should normally.
If you use this, you won't be able to use the pwm for other than backlight, also not the pin 33.

The driver:

lights.odroidc.so.zip

V2: Inversion of pwm duty selectable

(8.63 KiB) Downloaded 274 times

To copy to Odroid C1: adb push lights.odroidc.so /system/lib/hw/

[edit]
To support also screen like VU8 this version read bootarg backlight_pwm=yes|no|invert.
Need to add in boot.ini as follow:

Code: Select all

# Enable backlight_pwm
# backlight_pwm=yes, no, invert
backlight_pwm=yes

# Booting
setenv bootargs "root=/dev/mmcblk0p2 rw console=ttyS0,115200n8 no_console_suspend vdaccfg=${vdac_config} logo=osd1,loaded,${fb_addr},${outputmode},full hdmimode=${hdmimode} cvbsmode=${cvbsmode} hdmitx=${cecconfig} vout=${vout_mode} disablehpd=${disablehpd} ${disableuhs} androidboot.serialno=${fbt_id#} ir_remote=${ir_remote} usbcore.autosuspend=-1 ${selinuxopt} suspend_hdmiphy=${suspend_hdmiphy}} backlight_pwm=${backlight_pwm}"

The source code: https://github.com/joerg65/lights.

To control the backlight of the VU7+ there is to do a little tinkering. At the pin 4 of the PT4103 backlight driver must be soldered a resistor. I used a 330 Ohms type. But it should also be possible without resistor. Other than in this picture the EN pin on the VU7+ has pull up resistor 10k to be enabled always. I measured the current when the EN pin is connected to GND, it is about 0.5mA which comes from the pull up resistor: 5V divided by 10k. But I put a resistor, call it fear resistor . And glued it on the board and soldered carefully to the pin 4. This can be connected to the pin 33 of Odroid.

Bildschirmfoto vom 2017-06-01 20-44-16.png (10.52 KiB) Viewed 16300 times

DSC_0607.JPG (508.96 KiB) Viewed 16300 times

DSC_0608.JPG (273.87 KiB) Viewed 16300 times

[youtube]https://www.youtube.com/watch?v=mVvnLiKiksw[/youtube]

[odroid]

Thank you for a very useful tutorial for Vu7+ users.

[tobetter]

This is cool, @joerg, you did great work.

It might be a good idea to merge your code to ODROID source tree to build light.odroidc.so, so that it can control VU7 when it's attached. I am not sure if it is possible that ODROID can detect VU7 through EDID to enable backlight control.

[joerg]

Thank you. It need to be discussed if the driver should be merged to the tree. One can use this also for the hdmi board M.NT68676, so it should not depend on a lcd model. And once the lights.odroidc.so is in it's place, Android loads it automatically and then the pwm is used. Maybe to read an env variable from build.prop could be a solution.

[odroid]

How about the compatibility with Vu8C model?

[joerg]

I would need a function description for this two inputs of the VU8 as I don't know if it can be dimmed. In the script is refered only to the gpio97 pin 35 as On/Off. Or you can test it, maybe work out of the box?

[odroid]

It seems to be compatible.
http://odroid.com/dokuwiki/doku.php?id= ... l_with_pwm

I will check it early next week.

[joerg]

Value can be 0 to 1023 and lower value means brighter.
This is inverted, the driver works in the other direction. It would be possible to read a env variable and invert the value before send to pwm-ctrl. Need to add a little code for this but any idea what would be the best and most praticable way to pass a env variable? E.g BACKLIGHT_PWM: YES, INVERT, NO.

[odroid]

BACKLIGHT_PWM: YES, INVERT, NO.

It is very reasonable and understandable.

[joerg]

Updated the driver code to support also the inverted duty like it is needed for VU8.
I searched a lot, but didn't found a simple way to read a env variable. So I ended in reading the /proc/cmdline.
Question to the geeks: Is there not existing something simple like getenv()?

Code: Select all

        //check the bootargs for backlight_pwm
        FILE * fp;  
        char * line = NULL; 
        char * list;
        char * value;
        size_t len = 0;
        
        fp = fopen("/proc/cmdline", "r");                                                                                                                         
        if (fp != NULL) {
            getline(&line, &len, fp);
            list = strtok (line, " ");
            while (list != NULL)
            {
                LOGD ("%s\n",list);
                if (0 == strncmp(BACKLIGHT_PWM, list, 13)) {
                    env_backlight = strtok(list, "="); 
                    env_backlight = strtok(NULL, "=");
                    break;
                }
                list = strtok (NULL, " ");
            }
        }
        enable = false;
        invert = false;
        if (env_backlight != NULL) {
            LOGD("backlight_pwm : %s", env_backlight);
            
            if (0 == strncmp( BACKLIGHT_PWM_YES, env_backlight, 3 )) {
                enable = true;
            } else if (0 == strncmp( BACKLIGHT_PWM_NO, env_backlight, 2 )) {
                //enable = false;
                //return -EINVAL;
            } else if (0 == strncmp( BACKLIGHT_PWM_INV, env_backlight, 6 )) {
                enable = true;
                invert = true;
            } else { enable = false; }
        }

[odroid]

Thanks joerg !

We've released a new C2 Android update with the brightness control function.
http://odroid.com/dokuwiki/doku.php?id= ... allow_v3.0
There are options in boot.ini file.

Code: Select all

# Enable backlight_pwm
# disable : backlight "no"
# ODROID-VU5/7 : backlight "yes"
# ODROID-VU8 : backlight "invert"
setenv backlight_pwm "no"

We will release C1 update early next week.

[poptmartone]

This man is GREAT!!!!!

[joerg]

Thank you poptmartone!
And thank you odroid, for the great hardware. Very fast integration to the Android image and great wiki page. That's why so many users love the odroids.

[joerg]

I encountered a problem when connected the VU7+ to the otg port of the C1. When C1 (Lollipop) goes sleep it doesn't wake up when touch screen is touched. I saw in log that there are touch events, but display stays dark. There are also no backlight commands from Android framework. I can wake it up by command input keyevent 26, then the VU7+ becomes illuminated again.
In different, when it is connected to one of the 4 usb ports, C1 always wakes up and display is illuminated again when touchscreen is touched.
Also I have a VU7+ with old firmware (the one that need usb reconnection), this one is not affected. It wakes up always when touch event occurs.
If can't be found solution, I have to make a special usb adapter for the screen of my Alam Central, because very little space.

[joerg]

@odroid
Could you verify this? I tested also with the C2 Marshmallow, with the newer VU7+ connected to otg port, touches don't wake up the system, but moving of a connected mouse does wake up the system.
Connected to one of the type A usb ports, touches wake up the system.

[odroid]

If the VBUS is off in the display sleep mode, it will not wake the backlight up.
Please check the lsusb output via serial adb console when the display turns off.

[joerg]

Hi, as I described already there are touch events, but device dosn't wake up.

This logs are taken in sleeping mode:
lsusb

Code: Select all

Bus 001 Device 002: ID 05e3:0610
Bus 002 Device 002: ID 16b4:0705 <--
Bus 001 Device 001: ID 1d6b:0002
Bus 002 Device 001: ID 1d6b:0002
Bus 001 Device 004: ID 046d:c00e
Bus 001 Device 003: ID 7392:7811

getevent -lt /dev/input/event1 (touch at otg, does not wake up)

Code: Select all

[    1890.890140] EV_ABS       ABS_MT_TRACKING_ID   0000000f            
[    1890.890140] EV_ABS       ABS_MT_POSITION_X    00000162            
[    1890.890140] EV_ABS       ABS_MT_POSITION_Y    000000e3            
[    1890.890140] EV_KEY       BTN_TOUCH            DOWN                
[    1890.890140] EV_ABS       ABS_X                00000162            
[    1890.890140] EV_ABS       ABS_Y                000000e3            
[    1890.890140] EV_SYN       SYN_REPORT           00000000            
[    1890.922141] EV_ABS       ABS_MT_POSITION_X    0000017a            
[    1890.922141] EV_ABS       ABS_X                0000017a            
[    1890.922141] EV_SYN       SYN_REPORT           00000000            
[    1890.954141] EV_ABS       ABS_MT_POSITION_X    00000197            
[    1890.954141] EV_ABS       ABS_MT_POSITION_Y    000000e1            
[    1890.954141] EV_ABS       ABS_X                00000197            
[    1890.954141] EV_ABS       ABS_Y                000000e1            
[    1890.954141] EV_SYN       SYN_REPORT           00000000            
[    1890.986142] EV_ABS       ABS_MT_POSITION_X    000001cf            
[    1890.986142] EV_ABS       ABS_MT_POSITION_Y    000000da            
[    1890.986142] EV_ABS       ABS_X                000001cf            
[    1890.986142] EV_ABS       ABS_Y                000000da            

getevent -lt /dev/input/event4 (mice connected to type A usb, does wake up)

Code: Select all

[    2142.348357] EV_REL       REL_X                00000003            
[    2142.348357] EV_REL       REL_Y                00000001            
[    2142.348357] EV_SYN       SYN_REPORT           00000000            
[    2142.356363] EV_REL       REL_X                00000005            
[    2142.356363] EV_REL       REL_Y                00000003            
[    2142.356363] EV_SYN       SYN_REPORT           00000000            
[    2142.364363] EV_REL       REL_X                00000008            
[    2142.364363] EV_REL       REL_Y                00000003            
[    2142.364363] EV_SYN       SYN_REPORT           00000000            
[    2142.372378] EV_REL       REL_X                00000008            
[    2142.372378] EV_REL       REL_Y                00000002            
[    2142.372378] EV_SYN       SYN_REPORT           00000000            
[    2142.380369] EV_REL       REL_X                0000000a            
[    2142.380369] EV_REL       REL_Y                00000003 

getevent -lt /dev/input/event4 (other VU7+ touch connected to type A usb, does wake up)

Code: Select all

[    2476.217129] EV_ABS       ABS_MT_TRACKING_ID   00000005            
[    2476.217129] EV_ABS       ABS_MT_POSITION_X    00000246            
[    2476.217129] EV_ABS       ABS_MT_POSITION_Y    000000ea            
[    2476.217129] EV_KEY       BTN_TOUCH            DOWN                
[    2476.217129] EV_ABS       ABS_X                00000246            
[    2476.217129] EV_ABS       ABS_Y                000000ea            
[    2476.217129] EV_SYN       SYN_REPORT           00000000            
[    2476.289205] EV_ABS       ABS_MT_POSITION_X    00000244            
[    2476.289205] EV_ABS       ABS_MT_POSITION_Y    000000ec            
[    2476.289205] EV_ABS       ABS_X                00000244            
[    2476.289205] EV_ABS       ABS_Y                000000ec            
[    2476.289205] EV_SYN       SYN_REPORT           00000000            
[    2476.361189] EV_ABS       ABS_MT_POSITION_X    00000241            
[    2476.361189] EV_ABS       ABS_X                00000241            
[    2476.361189] EV_SYN       SYN_REPORT           00000000            
[    2476.457203] EV_ABS       ABS_MT_POSITION_X    00000240            
[    2476.457203] EV_ABS       ABS_X                00000240            
[    2476.457203] EV_SYN       SYN_REPORT           00000000            
[    2476.505215] EV_ABS       ABS_MT_POSITION_X    0000023e            
[    2476.505215] EV_ABS       ABS_X                0000023e            
[    2476.505215] EV_SYN       SYN_REPORT           00000000            
[    2476.553227] EV_ABS       ABS_MT_TRACKING_ID   ffffffff            
[    2476.553227] EV_KEY       BTN_TOUCH            UP                  
[    2476.553227] EV_SYN       SYN_REPORT           00000000

Now I have tested with C1+ and Lollipop. Yesterday with C2 and Marshmallow.

[odroid]

Ah... sorry for my misunderstanding.
We will check the issue.

[odroid]

We've tested it.
The Vu7+ wake-up function doesn't work on the OTG port either host ports of C2 Marshmallow.
We will keep looking into what makes the difference.

[joerg]

Thank you for verifying this. Actually I have a workaround: I switched on Daydream with option to dimm down during night time. For my project O.K., but nevertheless it should be looked further into this. As some user might have a issue with this, if connected with otg adapter tu VU7+.

[codewalker]

https://codewalkerster.blogspot.kr/2017 ... ke-up.html

http://odroid.com/dokuwiki/doku.php?id= ... allow_v3.1

[joerg]

Thank you, I will check this when I am back home.

[benwillcox]

This looks like a great mod many thanks, I'm going to test it with an RTD2662 based LCD driver when I get a chance. In the meantime, can you tell me what the PWM frequency is if you know it?
Also, does the backlight PWM level get restored immediately on power up, or does Android need to fully boot before the level is set?

Thanks
Ben

[odroid]

The default PWM frequency is set at 100Khz. But you can change it.
http://odroid.com/dokuwiki/doku.php?id= ... l_with_pwm

Android OS must run to load the PWM device driver.

[joerg]

@Ben: The level is set during Android boot animation, when the HAL drivers are loaded. Before this, the pin 33 is undefined. You probably would need to add a pull up resistor to the pin, to have full light untill the driver is loaded.

[benwillcox]

Thanks @odroid and @joerg, sounds perfect I'm looking forward to trying it out.

Ben

[benwillcox]

Hi, I tested this out today and of course the PWM works
I did find however that the default frequency seemed to be 1kHz not 100kHz.

There is an interesting issue with my LCD driver, I'm using one of these very commonly available boards: http://www.ebay.co.uk/itm/PCB800099-HDM ... 1684615018 and when driving the EN pin with the PWM I see lots of interference (horizontal lines) on the screen unless I use a PWM frequency higher than around 12kHz. This is the same issue when feeding PWM from another source i.e. an Arduino so nothing to do with the Odroid or this firmware addition but thought I would mention it.
The problem is that the higher the frequency the dimmer the display, my guess being that there is a minimum possible pulse length so with a higher PWM frequency the effective average OFF time gets longer. Maybe it's just a limitation of this type of board (I'm not sure the EN pin is actually designed to operate with PWM), but would be interested to know what PWM frequency works with the VU7 boards?
Do you know what defines the minimum OFF pulse period (i.e. at 100% brightness level control) and whether it can be changed?

Thanks,
Ben

[joerg]

Hi Ben, indeed the default pwm frequency is 1kHz. I used this when I tried my code with the VU7. As the frequency should be much smaller than the underlying frequency of the led driver, I found 1kHz is o.k. and should not be visible by human eye. As you stated, I think the input you used is not for pwm as it seems that the pwm is causing interferences to the video signal. On the other hand, if you use 12kHz it may be possible that the underlying led driver has not enough time to swing in until next off period comes, so the backlight loose some voltage.
I measured the pwm with oscilloscope. When duty is 100%, means 1023, and 1kHz, the off time is 1us.

[henri57]

I use the VS-TY2662-V1 ( know as PCB800099-V9 too) a generic LCD driver board.
As you've said the EN pin isn't compatible with PWM backlight so i soldered resistors and capacitor as for the VU-8C kit to use the PWM signal from pin 33 of the ODROID.
this function perfectly with setenv backlight_pwm "invert".
The only problem if found is :
from 0 to around 75 % slider PWM change from 2.2V to 0V and suddenly the PWM start again from 0.9V to 0V for 100% of slider.
I've taken this measure at pin 33 with a simple multimeter.
I've just modified the setenv parameter without any other command.

[codewalker]

Hi, henri57.
Thanks your bug report. Try this test version.

https://dn.odroid.com/S905/Android/test/marshmallow/

Here, Guide for Update.
https://codewalkerster.blogspot.kr/2016 ... -slow.html

I use the VS-TY2662-V1 ( know as PCB800099-V9 too) a generic LCD driver board.
As you've said the EN pin isn't compatible with PWM backlight so i soldered resistors and capacitor as for the VU-8C kit to use the PWM signal from pin 33 of the ODROID.
this function perfectly with setenv backlight_pwm "invert".
The only problem if found is :
from 0 to around 75 % slider PWM change from 2.2V to 0V and suddenly the PWM start again from 0.9V to 0V for 100% of slider.
I've taken this measure at pin 33 with a simple multimeter.
I've just modified the setenv parameter without any other command.

[henri57]

Hi, henri57.
Thanks your bug report. Try this test version.

https://dn.odroid.com/S905/Android/test/marshmallow/

No more problem. Thanks

[Jaguaruk]

can you do this for lollipop 5.1.1

[codewalker]

Try to update.

can you do this for lollipop 5.1.1

[east1]

I have odroid c2 and vu5 and want make workable backlight. Should it works with 200 Ohms resistor or i need only 330 Ohms fot that?

[joerg]

You can use also the 200 Ohms. As I wrote in the original post, the resistor is not really needed. I made it this way, because I can connect a wire very easy.