90 lines
2.9 KiB
C
90 lines
2.9 KiB
C
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/*
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Note: Previously this program did not unlock the extended registers,
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so it only worked if the registers happened to be unlocked.
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This program sets the 'memory clock' of Cirrus 5424/26/28 cards.
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The first three values could be set by utility programs that
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came with my card (AVGA3), but somewhat higher values seem to work (on my
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card at least). It may be that better and more recent Cirrus cards use a
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higher value as boot-up default. It should depend on DRAM speed, but it
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seems to be more dependant on the card logic.
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I have the impression that many Cirrus 542x cards suffer from horrible
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BIOS version/DRAM timing misconfigurations. Perhaps even some versions of
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MS-Windows drivers change the MCLK register. In any case, the boot-up BIOS
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default (0x1c) may be inappropriately low for the type of DRAM timing most
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cards use.
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Using a higher memory clock gives a very significant performance improvement;
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with high dot clock modes (like 640x480x16M or 1150x900x256) performance can
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be more than twice that of the standard 50 MHz clock. This goes for both
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(VLB) framebuffer access and accelerated features (bitblt). This also helps
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XFree86 server performance, but only if the XFree86 Cirrus driver doesn't
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set the memory clock register (it should work for XFree86 1.3 and 2.0).
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Use at your own risk!
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Note that the 'dot clock' is something entirely different. There does not
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seem to be much correlation between the two (i.e. if a high dot clock gives
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screen problems, using a high memory clock is not likely to fix it, other
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than improving speed).
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*/
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#define NEW_MCLK 0x1C /* Default value */
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/* #define NEW_MCLK 0x26 *//* High value to test XFree86 */
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <vga.h>
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#include <sys/io.h> /* For port I/O macros. */
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#define OUTB(a,d) outb(d,a)
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int
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main (void)
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{
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vga_init ();
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if (vga_getcurrentchipset () != CIRRUS)
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{
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printf ("Not a Cirrus.\n");
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printf ("Continue anyway (y/n)?\n");
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if (getchar () != 'y')
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return -1;
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}
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/* Unlock extended registers. */
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OUTB (0x3c4, 0x06);
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OUTB (0x3c5, 0x12);
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/*
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Tested on VLB AVGA3 CL-GD5426 on 40MHz VLB
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0x1c 50 MHz (boot-up default)
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0x21 59
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0x22 62
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0x23 OK
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0x24 OK
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0x25 OK
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0x26 OK [This corresponds to the highest value
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mentioned in the databook (which does
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not mean that it is supposed to work
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on all cards); the book also says the
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parts are not specified for more than
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50 MHz].
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0x27 occasional loose pixels
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0x28 occasional problems
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0x29 some problems
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0x2A 16M/textmode problems
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0x2c 256/32k color problems
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*/
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OUTB (0x3c4, 0x1f);
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printf ("Old MCLK value: %02x\n", inb (0x3c5));
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OUTB (0x3c4, 0x1f);
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OUTB (0x3c5, NEW_MCLK);
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printf ("New MCLK value: %02x\n", NEW_MCLK);
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return 0;
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}
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