LCD and Capacitive touch drivers for Debian on BB black

[ksc...@3ztelecom.com]

My company is building a product based on the Beaglebone black as a reference design.  We will be adding a touch screen with a capacitive touch screen controller (Mitsubishi) using either a serial or USB protocol.  The LCD display will be wired to the BB similarly to the BB-VIEW cap (24 bit RGB).  We won't be using the resistive touch screen hardware on the BB.

As I have no Linux driver development experience I hope I can make use of an existing driver to support these two pieces of hardware.  If necessary I can adjust parameters in the driver source code for any differences in the hardware.  I suspect that the touch screen controller already emulates either a USB HID mouse, or a serial mouse so an existing driver for one of these would be a starting point.

Then there is the matter of which Linux kernel source tree to use.  We will need QT support (I plan on using QT for the graphical framework for our application).  So far some of the best instructions on cross tools for development for the BB suggest using Debian Jessie as the host platform, which would imply using the same for the target, however I've also heard that the TI developed kernels may be better.

As my programming strengths are more on the application side than the kernel side (I have done development work under Linux, and have configured and built kernels before, but not entire system images for cross builds), I am looking for some advice on how to get our platform working.  Except for the LCD/Touchscreen the only other hardware we will need to bring on board will be additional USB serial ports and hubs, but support for these should already be solidly in place in any base system we start with.

Thanks in advance for any help.

[Robert Nelson]

On Mon, Oct 26, 2015 at 3:21 PM, <ksc...@3ztelecom.com> wrote:
> My company is building a product based on the Beaglebone black as a
> reference design. We will be adding a touch screen with a capacitive touch
> screen controller (Mitsubishi) using either a serial or USB protocol. The
> LCD display will be wired to the BB similarly to the BB-VIEW cap (24 bit
> RGB). We won't be using the resistive touch screen hardware on the BB.

How far are you in the design?

aka, DON"T use the BB-VIEW's 24bit rgb lines design, they swapped RED
& BLUE, which will make things a PAIN in the REAR for YOU!

If you want 24bit steal/borrow the chipsee 24bit lcd design...

> As I have no Linux driver development experience I hope I can make use of an
> existing driver to support these two pieces of hardware. If necessary I can
> adjust parameters in the driver source code for any differences in the
> hardware. I suspect that the touch screen controller already emulates
> either a USB HID mouse, or a serial mouse so an existing driver for one of
> these would be a starting point.
>
> Then there is the matter of which Linux kernel source tree to use. We will
> need QT support (I plan on using QT for the graphical framework for our
> application). So far some of the best instructions on cross tools for
> development for the BB suggest using Debian Jessie as the host platform,
> which would imply using the same for the target, however I've also heard
> that the TI developed kernels may be better.
>
> As my programming strengths are more on the application side than the kernel
> side (I have done development work under Linux, and have configured and
> built kernels before, but not entire system images for cross builds), I am
> looking for some advice on how to get our platform working. Except for the
> LCD/Touchscreen the only other hardware we will need to bring on board will
> be additional USB serial ports and hubs, but support for these should
> already be solidly in place in any base system we start with.

Regards,

--
Robert Nelson
https://rcn-ee.com/

[ksc...@3ztelecom.com]

Thanks for the info!

Our board layout guy hasn't yet committed the final gerbers yet so we can change this.  We were actually thinking about using only a 16 bit color depth (5/6/5) because we thought the other 8 bits were 'shared' with other functions.  

BTW when you say they swapped the red and the blue I assume you mean that the LCDbit numbers (0-23) assignments on the BBB are mis-assigned, correct?

As far as the driver is concerned I assume that we would have to change timing constants somewhere to match our panel, either in the source code or a config file that is pulled in on module load.  I also have no idea about the touch screen which has a serial interface (will connect to one of the available BBB uarts) and the protocol is similar to serial/usb mice.

[Robert Nelson]

On Wed, Oct 28, 2015 at 11:09 AM, <ksc...@3ztelecom.com> wrote:
> Thanks for the info!
>
> Our board layout guy hasn't yet committed the final gerbers yet so we can
> change this. We were actually thinking about using only a 16 bit color
> depth (5/6/5) because we thought the other 8 bits were 'shared' with other
> functions.

okay, if your going to use the 16bit now, use this schematic for reference..

https://github.com/CircuitCo/BeagleBone-LCD7-RevA3

> BTW when you say they swapped the red and the blue I assume you mean that
> the LCDbit numbers (0-23) assignments on the BBB are mis-assigned, correct?

the designers behind the bb-view messed it up...

> As far as the driver is concerned I assume that we would have to change
> timing constants somewhere to match our panel, either in the source code or
> a config file that is pulled in on module load. I also have no idea about

Timing are glass specific:

https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-BONE-LCD7-01-00A3.dts#L240-L273

What's nice, the docs are written with regards to most glass
manufacture's datasheet:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/video/display-timing.txt

> the touch screen which has a serial interface (will connect to one of the
> available BBB uarts) and the protocol is similar to serial/usb mice.

That'll probably be fine..