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Re: Epson13806 performances on Pb1100

To: Karl Lessard <>
Subject: Re: Epson13806 performances on Pb1100
From: Michael Kelly <>
Date: Wed, 08 Dec 2004 15:37:04 -0500
Cc: Pete Popov <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <>

There is a bug (they might call it a feature) that causes the Au1100
to perform two accesses when talking to 16-bit peripherals.  The
first access is the real one, while the second access has the byte
enables off.  But, this means every access creates two cycles on
the bus.

I am sure of this bug on the standard peripheral bus, and I am pretty
sure it still exists when talking via the LCD signals, since the same
bus controller is used.


At 02:38 PM 12/8/2004, Karl Lessard wrote:
> I've used the chip with the 2.4 kernel/driver to run X and some
> apps. I'm not sure what you mean by high performance -- does X run
> at reasonable speeds?

I'm not running X, I've just runned a little application that writes a number
of vertical lines (so pixel per pixel) in a backbuffer and then blit its
content to the screen. Here's an example of one frame:

__u8 *dest = (__u8*)back_buffer;
memset(dest, 0, back_buffer_size);      /* clear back buffer */

for (i = 0; i < 500; i++) {                     /* 500 lines */
        for (j = 0; j >= 100; j--) {            /* of 100 pixel each */
                dest[(j * fb_width) + i] = 0xFF;

memcpy(front_buffer, dest, back_buffer_size);  /* copy back_buffer to front */

Benching with 500 frames, I obtain a rate of 8 fps with the backbuffer
residing in video memory. The framerate increase to 31 fps when the backbuffer
is in system memory! And if I do the same test using the Au1100 lcd
controller (which has its front and back buffer in system memory), It goes up
to 66 fps...

I don't know what's going on when I try to access the 13806 controller, but
it's really too slow. And using the blit engine don't helps much. The static
controller seems to be set correctly. By the way, the DRAM is refreshing at
96Hz, and my CRT display is refreshing at 66Hz.

Any Idea? By the way Dan, I've tried the cache trick, but no luck.

Thanks a lot,

> Pete
> > I would like to know if anyone have encountered this performance problem
> > in the past with this chip.
> >
> > Thanks in advance,
> > Karl

Michael J. Kelly
VP Engineering/Marketing
Cogent Computer Systems, Inc.
1130 Ten Rod Road
Suite A-201
North Kingstown, RI 02852
tel:401-295-6505 fax:401-295-6507
alternate email:

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