using display module with Logibone

tarik

Hi,

when I treid to use my Display Modules 7" LCD DispCapew/tch for BeagleBone Black with logibon+beaglebone black I got nothing on teh desplay, the Power LED in the display was green.

What do I need to do to get the display to work?

Thanks guys for your help

Tarik

mjones

Hi Tarik,

It is possible that there is a conflict with the default device tree setup for the LOGI image and the use of the LCD you are trying to use.  Can you provide a datasheet to you LCD you are using?  We will need to look at the pin usage of the cape ensure that there is no overlap of pin usage with current device tree configuration. Jonathan will be creating a wiki page that outlines the process of modifying your own device tree files to enable/disable pin functionality as need to use such alternative capes.

Cheers,

Mike

Here is a link to the ongoing wiki page that will discuss kernel driver development and device tree modifications.

http://valentfx.com/wiki/index.php?title=Develop_new_driver_for_LOGI-Bone

@jpiat

tarik

thanks Mike, here is a link to the display datatsheet:

http://www.mouser.com/ds/2/451/4DCAPE-70T_datasheet_R_1_0-270418.pdf

Tarik

 

jpiat

There is a good chance that the touchscreen conflicts with the logibone with the default device tree setup. The logibone uses spi to load the FPGA and the display may use spi for the touchscreen. The problem with device tree is that if two device tree configurations uses the same peripheral, only one of them gets loaded. To use your touchscreen cape we will need to deactivate the spi in the logibone device tree configuration to avoid this conflict. What may also conflicts is the address of the identification eeprom used by both capes ... can you boot your board with both cape plugged in and then do a dmesg to see how device tree reacts ?

Regards,

Jonathan piat

jpiat

I just checked the documentation and the cape does not use spi. It use some gpio though son I ll need to check if those does not conflicts with the logibone.

tarik

thanks Jon for the help

tarik

i booted with BeagleBone black , logi bone and the dispaly plugged -in  and didnt get anything on my cap(LCD display) so I did  dmesg and got:
[ I think time stamps ] [drm:drm_ioctl], pid=179, cmd =0xc01864b1, nr=0xb1, dev 0xe200, auth=1
[xxx.xxxxxx] [drm:drm_ioctl], ret = -38

I got these two lines printed  many times

Tarik

mjones

Hi Tarik,

Can you remove the logi-bone and plug in the LCD and see if it works.  This will test whether the current device tree overlay is compatible.  It it does not work, I think the next step would be to create an overlay that works with the LCD.  Then plug the logi-bone back in and and ensure that it still works.  If not then there would need to be further testing to see what is conflicing on the logi-bone.  Jonathan can comment on this process as well.  Jonathan, did you see any conflicts with the pinout of the LCD and the logi-bone? @jpiat

tarik

actually right now I have the LCD display plug-in the beaglebone black and it is working fine, but when I plug the logibone to the BBB and plugin the LCD,  the display doesnt work

mjones

OK.  This indicates that either the logi-bone or the overlay is conflicting.  If you need help Jonathan or I will need to create a new overlay for your testing . 

In the mean time you can have a look at this great guide on the device tree and overlays for the BBB.  This has pretty detailed instructions on how to create an overlay.  You can directly load/unload custom overlays as need to debug which pins may be conflicting.  See the below links.  @jpiat ;and I will look into this further as time allows.  In the mean time this below information should help you get going.

great links regarding the device tree usage on the BBB

http://elinux.org/Beagleboard:BeagleBoneBlack#Extremely_Useful_Links

very good overall step by step guide on using overlays

http://derekmolloy.ie/gpios-on-the-beaglebone-black-using-device-tree-overlays/

loading and unloading overlays:

https://learn.adafruit.com/introduction-to-the-beaglebone-black-device-tree/exporting-and-unexporting-an-overlay

tarik

cool thanks guys!

Tarik

mjones

I should also note that my guess would be that it is an overlay issue rather than fpga IO state issue.  The FPGA pins are all in HiZ until it is configured, which would should allow the logi-bone to be passive until it is configured with the corresponding IO states of the bitfiles.  

mjones

Here are some possibly conflicting pins.  The pinout shows the 4D systems pinout.  I have circled green with what should be ok and red where there may some conflicts that will need to be looked into.   

mjones

And here is the LOGI-Bone pin usage pinout for reference.  Taken form the LOGI Bone manual.

mjones

Hi Tarik,

I believe that the lcd module eeprom is loading it's own overlay, which is likely conflicting with the logi-bone overlay which it is trying to use.  I think that the logi-bone has priority for it's eeprom overlay as it is assigned address "00" (can be changed on the bottom side of the logi-bone using the solder jumpers).  

Based on what I can see the most likely the conflict comes from the above mentioned pins, most likely the be1n gpmc pin. I think that you can safely modify the logi-bone overlay to remove the gpmc be1n pin as it is not currently being used by the gpmc drivers, though it may be enable for use at some point down the road,  @jpiat ;can verify this.  

The logi-bone is currently configuring the SPI D1 (MOSI) pin as would be needed by the LCD.  So it does not seem to be a problem.

Based on the schematic for the LCD the analog pins are used for the touch display.  You will need to remove the resistors .  You can safely remove the resistors if they turn out to be conflicting resistor on the logi-bone (R44-R37) as can be seen in this image.

I think that we need is to see how the LCD is configuring the GPIO for it's usage and compare it to the logi-bone overlay.  I cannot do this as I do not have an LCD.  Maybe I can get one on order.  Can you run the following commands after booting the BBB with only the LCD attached.  It would be best to copy the outputs into a file and then attach here.  

"sudo cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins"

"sudo cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pinmux-pins"