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xf86cvt.c

/*
 * Copyright 2005-2006 Luc Verhaegen.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * The reason for having this function in a file of its own is
 * so that ../utils/cvt/cvt can link to it, and that xf86CVTMode
 * code is shared directly.
 */

#ifdef HAVE_XORG_CONFIG_H
#include <xorg-config.h>
#else
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#endif

#include "xf86.h"
#include "xf86Modes.h"

#include <string.h>

/*
 * Generate a CVT standard mode from HDisplay, VDisplay and VRefresh.
 *
 * These calculations are stolen from the CVT calculation spreadsheet written
 * by Graham Loveridge. He seems to be claiming no copyright and there seems to
 * be no license attached to this. He apparently just wants to see his name
 * mentioned.
 *
 * This file can be found at http://www.vesa.org/Public/CVT/CVTd6r1.xls
 *
 * Comments and structure corresponds to the comments and structure of the xls.
 * This should ease importing of future changes to the standard (not very
 * likely though).
 *
 * About margins; i'm sure that they are to be the bit between HDisplay and
 * HBlankStart, HBlankEnd and HTotal, VDisplay and VBlankStart, VBlankEnd and 
 * VTotal, where the overscan colour is shown. FB seems to call _all_ blanking
 * outside sync "margin" for some reason. Since we prefer seeing proper
 * blanking instead of the overscan colour, and since the Crtc* values will
 * probably get altered after us, we will disable margins altogether. With
 * these calculations, Margins will plainly expand H/VDisplay, and we don't
 * want that. -- libv
 *
 */
DisplayModePtr
xf86CVTMode(int HDisplay, int VDisplay, float VRefresh, Bool Reduced,
          Bool Interlaced)
{
    DisplayModeRec  *Mode = xnfcalloc(1, sizeof(DisplayModeRec));

    /* 1) top/bottom margin size (% of height) - default: 1.8 */
#define CVT_MARGIN_PERCENTAGE 1.8    

    /* 2) character cell horizontal granularity (pixels) - default 8 */
#define CVT_H_GRANULARITY 8

    /* 4) Minimum vertical porch (lines) - default 3 */
#define CVT_MIN_V_PORCH 3

    /* 4) Minimum number of vertical back porch lines - default 6 */
#define CVT_MIN_V_BPORCH 6

    /* Pixel Clock step (kHz) */
#define CVT_CLOCK_STEP 250

    Bool Margins = FALSE;
    float  VFieldRate, HPeriod;
    int  HDisplayRnd, HMargin;
    int  VDisplayRnd, VMargin, VSync;
    float  Interlace; /* Please rename this */

    /* CVT default is 60.0Hz */
    if (!VRefresh)
        VRefresh = 60.0;

    /* 1. Required field rate */
    if (Interlaced)
        VFieldRate = VRefresh * 2;
    else
        VFieldRate = VRefresh;

    /* 2. Horizontal pixels */
    HDisplayRnd = HDisplay - (HDisplay % CVT_H_GRANULARITY);

    /* 3. Determine left and right borders */
    if (Margins) {
        /* right margin is actually exactly the same as left */
        HMargin = (((float) HDisplayRnd) * CVT_MARGIN_PERCENTAGE / 100.0);
        HMargin -= HMargin % CVT_H_GRANULARITY;
    } else
        HMargin = 0;

    /* 4. Find total active pixels */
    Mode->HDisplay = HDisplayRnd + 2*HMargin;

    /* 5. Find number of lines per field */
    if (Interlaced)
        VDisplayRnd = VDisplay / 2;
    else
        VDisplayRnd = VDisplay;

    /* 6. Find top and bottom margins */
    /* nope. */
    if (Margins)
        /* top and bottom margins are equal again. */
        VMargin = (((float) VDisplayRnd) * CVT_MARGIN_PERCENTAGE / 100.0);
    else
        VMargin = 0;

    Mode->VDisplay = VDisplay + 2*VMargin;

    /* 7. Interlace */
    if (Interlaced)
        Interlace = 0.5;
    else
        Interlace = 0.0;

    /* Determine VSync Width from aspect ratio */
    if (!(VDisplay % 3) && ((VDisplay * 4 / 3) == HDisplay))
        VSync = 4;
    else if (!(VDisplay % 9) && ((VDisplay * 16 / 9) == HDisplay))
        VSync = 5;
    else if (!(VDisplay % 10) && ((VDisplay * 16 / 10) == HDisplay))
        VSync = 6;
    else if (!(VDisplay % 4) && ((VDisplay * 5 / 4) == HDisplay))
        VSync = 7;
    else if (!(VDisplay % 9) && ((VDisplay * 15 / 9) == HDisplay))
        VSync = 7;
    else /* Custom */
        VSync = 10;

    if (!Reduced) { /* simplified GTF calculation */

        /* 4) Minimum time of vertical sync + back porch interval (Ás) 
         * default 550.0 */
#define CVT_MIN_VSYNC_BP 550.0

        /* 3) Nominal HSync width (% of line period) - default 8 */
#define CVT_HSYNC_PERCENTAGE 8

        float  HBlankPercentage;
        int  VSyncAndBackPorch, VBackPorch;
        int  HBlank;

        /* 8. Estimated Horizontal period */
        HPeriod = ((float) (1000000.0 / VFieldRate - CVT_MIN_VSYNC_BP)) / 
            (VDisplayRnd + 2 * VMargin + CVT_MIN_V_PORCH + Interlace);

        /* 9. Find number of lines in sync + backporch */
        if (((int)(CVT_MIN_VSYNC_BP / HPeriod) + 1) < (VSync + CVT_MIN_V_PORCH))
            VSyncAndBackPorch = VSync + CVT_MIN_V_PORCH;
        else
            VSyncAndBackPorch = (int)(CVT_MIN_VSYNC_BP / HPeriod) + 1;

        /* 10. Find number of lines in back porch */
        VBackPorch = VSyncAndBackPorch - VSync;

        /* 11. Find total number of lines in vertical field */
        Mode->VTotal = VDisplayRnd + 2 * VMargin + VSyncAndBackPorch + Interlace
            + CVT_MIN_V_PORCH;

        /* 5) Definition of Horizontal blanking time limitation */
        /* Gradient (%/kHz) - default 600 */
#define CVT_M_FACTOR 600

        /* Offset (%) - default 40 */
#define CVT_C_FACTOR 40

        /* Blanking time scaling factor - default 128 */
#define CVT_K_FACTOR 128

        /* Scaling factor weighting - default 20 */
#define CVT_J_FACTOR 20

#define CVT_M_PRIME CVT_M_FACTOR * CVT_K_FACTOR / 256
#define CVT_C_PRIME (CVT_C_FACTOR - CVT_J_FACTOR) * CVT_K_FACTOR / 256 + \
        CVT_J_FACTOR

        /* 12. Find ideal blanking duty cycle from formula */
        HBlankPercentage = CVT_C_PRIME - CVT_M_PRIME * HPeriod/1000.0;

        /* 13. Blanking time */
        if (HBlankPercentage < 20)
            HBlankPercentage = 20;

        HBlank = Mode->HDisplay * HBlankPercentage/(100.0 - HBlankPercentage);
        HBlank -= HBlank % (2*CVT_H_GRANULARITY);
        
        /* 14. Find total number of pixels in a line. */
        Mode->HTotal = Mode->HDisplay + HBlank;

        /* Fill in HSync values */
        Mode->HSyncEnd = Mode->HDisplay + HBlank / 2;

        Mode->HSyncStart = Mode->HSyncEnd - 
            (Mode->HTotal * CVT_HSYNC_PERCENTAGE) / 100;
        Mode->HSyncStart += CVT_H_GRANULARITY - 
            Mode->HSyncStart % CVT_H_GRANULARITY;

        /* Fill in VSync values */
        Mode->VSyncStart = Mode->VDisplay + CVT_MIN_V_PORCH;
        Mode->VSyncEnd = Mode->VSyncStart + VSync;

    } else { /* Reduced blanking */
        /* Minimum vertical blanking interval time (Ás) - default 460 */
#define CVT_RB_MIN_VBLANK 460.0

        /* Fixed number of clocks for horizontal sync */
#define CVT_RB_H_SYNC 32.0

        /* Fixed number of clocks for horizontal blanking */
#define CVT_RB_H_BLANK 160.0

        /* Fixed number of lines for vertical front porch - default 3 */
#define CVT_RB_VFPORCH 3

        int  VBILines;

        /* 8. Estimate Horizontal period. */
        HPeriod = ((float) (1000000.0 / VFieldRate - CVT_RB_MIN_VBLANK)) / 
            (VDisplayRnd + 2*VMargin);

        /* 9. Find number of lines in vertical blanking */
        VBILines = ((float) CVT_RB_MIN_VBLANK) / HPeriod + 1;

        /* 10. Check if vertical blanking is sufficient */
        if (VBILines < (CVT_RB_VFPORCH + VSync + CVT_MIN_V_BPORCH))
            VBILines = CVT_RB_VFPORCH + VSync + CVT_MIN_V_BPORCH;
        
        /* 11. Find total number of lines in vertical field */
        Mode->VTotal = VDisplayRnd + 2 * VMargin + Interlace + VBILines;

        /* 12. Find total number of pixels in a line */
        Mode->HTotal = Mode->HDisplay + CVT_RB_H_BLANK;

        /* Fill in HSync values */
        Mode->HSyncEnd = Mode->HDisplay + CVT_RB_H_BLANK / 2;
        Mode->HSyncStart = Mode->HSyncEnd - CVT_RB_H_SYNC;

        /* Fill in VSync values */
        Mode->VSyncStart = Mode->VDisplay + CVT_RB_VFPORCH;
        Mode->VSyncEnd = Mode->VSyncStart + VSync;
    }

    /* 15/13. Find pixel clock frequency (kHz for xf86) */
    Mode->Clock = Mode->HTotal * 1000.0 / HPeriod;
    Mode->Clock -= Mode->Clock % CVT_CLOCK_STEP;

    /* 16/14. Find actual Horizontal Frequency (kHz) */
    Mode->HSync = ((float) Mode->Clock) / ((float) Mode->HTotal);

    /* 17/15. Find actual Field rate */
    Mode->VRefresh = (1000.0 * ((float) Mode->Clock)) / 
        ((float) (Mode->HTotal * Mode->VTotal));

    /* 18/16. Find actual vertical frame frequency */
    /* ignore - just set the mode flag for interlaced */
    if (Interlaced)
        Mode->VTotal *= 2;

    {
        char  Name[256];
        Name[0] = 0;

        snprintf(Name, 256, "%dx%d", HDisplay, VDisplay);

        Mode->name = xnfalloc(strlen(Name) + 1);
        memcpy(Mode->name, Name, strlen(Name) + 1);
    }

    if (Reduced)
        Mode->Flags |= V_PHSYNC | V_NVSYNC;
    else
        Mode->Flags |= V_NHSYNC | V_PVSYNC;

    if (Interlaced)
        Mode->Flags |= V_INTERLACE;

    return Mode;
}

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