Hardware Reference
In-Depth Information
There is at least one drawback to this device. It uses DisplayLink, a technology that
allows for an additional monitor and graphics device to be connected via USB.
Unfortunately, this means that the Mimo 720 is not connected to or using the
Raspberry Pi GPU. The result is that it is not possible to use it as a VideoCore output
device, and it is not powerful enough to drive anything needing high-quality video
performance or acceleration on its own.
So, while it might seem perfect to use in a car seat-back multimedia player hack,
we would not recommend it for that use case. There are, however, plenty of other
cases where it's still a handy solution!
The Mimo 720 is technically two devices in one unit: an 800 x 480 LCD DisplayLink
monitor and an e2i Technology, Inc. USB touchpanel. Linux detects these devices
separately, so it is important for your Raspberry Pi Linux kernel to support for both of
them.
Installing and Enabling Drivers
You can make the Mimo 720 available as a monitor to Linux via two kernel drivers,
either the USB Display Link Framebuffer Driver ( CONFIG_FB_UDL in Kconfig -speak,
udlfb.ko as a module) or the USB Display Link Kernel Mode Setting (KMS) driver
( CONFIG_DRM_UDL in Kconfig -speak, udl.ko as a module). The UDL Kernel Mode Setting
driver does not work as well for this use as the UDL Framebuffer Driver. The KMS driver
is likely to eventually be the better choice, but in the interim, the Framebuffer Driver
works great for our hacking needs.
The e2i Technology touchpanel portion of the device is driven by the USB Touchscreen
Driver ( CONFIG_TOUCHSCREEN_USB_COMPOSITE in Kconfig -speak, usbtouchscreen.ko as a
module).
Neither the USB Touchscreen Driver nor the UDL Framebuffer Driver is enabled by
default in the prebuilt kernels provided by the Raspberry Pi Foundation, and thus,
almost never present in Raspberry Pi Linux distribution images, but this is easily rem-
edied with a custom kernel, which you can build from source with the instructions in
“Install a New Kernel” on page 85 .
When you build your custom kernel for this hack, you will need to be sure that you
configure it so that these additional drivers are also built. As a reminder, you can con-
figure which drivers and options to build using make menuconfig .
 
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