[linrad] VESA

[Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxx>]

Hi All,

The VESA driver of svgalib-1.4.3 is very slow because 
Linrad writes pixels in the order order of increasing 
frequency or time (the order in which the data points 
are stored). This means that the VESA driver will have 
to remap it's memory each time the vertical separation 
between two pixels is too large (not very large)

Linrad-01.17 and earlier versions do not work well with
the VESA driver of svgalib-1.4.3. Overrun errors occur 
when spectra change rapidly causing the need to move 
many pixels. It has been possible to avoid these 
problems by make the window sizes modest or by averaging 
over many transforms so the pixels do not move so fast.

Linrad-01.18 works well with the svgalib-1.4.3 VESA 
driver on reasonably fast computers - but not for the 
oscilloscope functions.

I have installed svgalib-1.9.18 today. I needed assistance
from Matan Ziv-Av, head of svgalib.org because it does not 
install automatically under Red Hat 9. The difference in
speed of the graphics is most remarkable. The VESA driver
"VESA driver, 65536KB VBE3" of svgalib-1.9.18 runs about 
300 times faster than the 1.4.3 driver. Oscilloscopes run
faster on the screen than one can see (I will have to add 
a trigger function some day...) 

Redrawing the timf2 oscilloscope at 100 Hz (9 tracks, half 
the screen width) requires about 15 % of the CPU power 
of my PentiumIV 2.7GHz with the new driver. The time to 
redraw it once with the old driver was about half a 
second (useless).

The problem with installing svgalib-1.9.18 is related to
a feature called -rmap VM which is included in Red Hat 
distributions. (It is a feature that makes the handling of
virtual memory more efficient.)

If there is anyone on this list who knows how one can find
out if the -rmap VM feature is enabled in the kernel for the
svgalib Makefile to know, Matan Ziv-Av would be grateful for
some help so he can make the next svgalib easier to install.

              ---------- (from Matan) -----------

> The problem is that RH kernel includes a feature (rmap VM), 
> which is hard (at least, for me) to find. To compile 
> the module anyway, make sure you have the latest version 
> (1.9.18) and edit the file kernel26compat.h, changing line 10, so that 
> it is a copy of line 22 ( so that io_remap_page_range() sees 5 
> arguments). There might be similar issue with minor versus MINOR, which 
> requires similar changes near the end of the file.
.
.
.
> Maybe you can help me here - all that is needed here is a 
> gcc pre-processor trick that will find out if the rmap VM is used.
                     ---------------------------

I had to use Makefile.alt to compile svgalib_helper.

73

Leif  /  SM5BSZ



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