nanogui: qn. on offscreen mem. transfer / h.w. integration
Subject:
qn. on offscreen mem. transfer / h.w. integration
From:
sean machin ####@####.####
Date:
19 Jul 2006 19:16:04 +0100
Message-Id: <44BE76CF.5040300@yahoo.com>
Hi All,
I'm using Nano-X 0.91 on a custom ARM system using uCLinux. On this
particular system the CPU communicates with
a separate LCD controller via a fast shared serial line. The LCD
controller has it's own onboard memory for storing pixel
data. I created a custom Nano-X driver for this LCD based on one of the
samples in the distribution.
My question is where is the optimal place in the code for transferring
data from the CPU's memory buffer (storing
an image of what is to be sent to the LCD) to the LCD controller itself?
Originally I had each of the low level driver routines such as
LCD_drawpixel(), LCD_drawvline() etc. send
out the data to the LCD controller on each call. This did work but was
quite slow for high level routines such as text and bitmap
rendering as the LCD must be setup with col & page registers before you
send down the pixel data.
My next optimization was to not perform any writes to the LCD in the low
level driver pixel/line routines, but have
those routines instead just set bits on an offscreen memory buffer in
the CPU's address space. I then hacked in an extra "Flush"
command into the driver which transfers the data in the offscreen buffer
to the LCD's memory in one single
block of writes.
This technique works OK, except I had to hack in calls to the new Flush
command into the higher level Gd
functions such as GdText() and GdDrawImage(). This is starting to get
too hacky for my liking.
Can anyone suggest a better method of efficiently getting the pixel data
to the LCD in a h.w. configuration like mine?
Thanks,
Sean
BTW : Good work Greg & others on Nano-X, we like it a lot here.
