A frame buffer device is a memory device, such as /dev/mem, and it has features similar
to a memory device. Users can read it, write to it, seek to some location in it, and mmap()
it (the main use). The difference is that the memory that appears in the special file is not
the whole memory, but the frame buffer of some video hardware.
The EPDC frame buffer driver ( drivers/video/mxc/mxc_epdc_fb.c) interacts closely with
the generic Linux frame buffer driver (drivers/video/fbmem.c).
For additional details on the frame buffer device, please refer to documentation in the
Linux kernel found in Documentation/fb/framebuffer.txt.
9.3.2 EPDC Frame Buffer Driver Extensions
E Ink display technology, in conjunction with the EPDC, has several features that
distinguish it from standard LCD-based frame buffer devices. These differences
introduce the need for API extensions to the frame buffer interface. The EPDC refreshes
the E Ink display asynchronously and supports partial screen updates. Therefore, the
EPDC requires notification from the user when the frame buffer contents have been
modified and which region needs updating. Another unique characteristic of EPDC
updates to the E Ink display is the long screen update latencies (between 300-980ms),
which introduces the need for a mechanism to allow the user to wait for a given screen
update to complete.
The custom API extensions to the frame buffer device are accessible both from user
space applications and from within kernel space. The standard device IOCTL interface
provides access to the custom API for user space applications. The IOCTL extensions,
along with relevant data structures and definitions, can be found in include/linux/
mxcfb.h. A full description of these IOCTLs can be found in the Programming Interface
section
.
For kernel mode access to the custom API extensions, the IOCTL interface should be
bypassed in favor of direct access to the underlying functions. These functions are
included in include/linux/mxcfb_epdc_kernel.h, and are documented in the Programming
Interface section
9.3.3 EPDC Panel Configuration
The EPDC driver is designed to flexibly support E Ink panels with a variety of panel
resolutions, timing parameters, and waveform modes. The EPDC driver is kept panel-
agnostic through the use of an EPDC panel mode structure, mxc_epdc_fb_mode, which
can be found in arch/arm/plat-mxc/include/mach/epdc.h.
Chapter 9 Electrophoretic Display Controller (EPDC) Frame Buffer Driver
i.MX 6Solo/6DualLite Linux Reference Manual, Rev. L3.0.35_4.1.0, 09/2013
Freescale Semiconductor, Inc.
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