/* SCROLL.C scrolling function module.

   Copyright (c) 1995 Lin Ke-Fong, Ethereal Software.
*/

#include <conio.h>
#include "mpvga.h"

/* %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% */
void MPVGA_SetVStart (int Sx, int Sy)

{
  long int l;
  int shft, x;
  long int *Ptr;

  shft = 5;
  l = ((320 * Sy) + Sx) << 6;

  switch (MPVGA_ChipType) {

    case __Acer     : modinx(CRTC,0x81,0x30,l >> 20); break;

    case __Ahead    : {
      if ((rdinx(GRC,0x0C) & 0x20) > 0) l >>= 1;
      modinx(GRC,0x1C,3,l >> 24);
      break;
    }

    case __ALG      : {
      if ((rdinx(GRC,0x0C) & 0x10) != 0) l >>= 1;
      modinx(CRTC,0x20,7,l >> 24);
      break;
    }

    case __Alliance : modinx(CRTC,0x1C,0x0F,l >> 24); break;

    case __ARK      : {
      if ((rdinx(CRTC,0x46) & 4) > 0) l >>= 1;
      modinx(CRTC,0x40,7,l >> 24);
      break;
    }

    case __ATI      : {
      if ((MPVGA_ChipVer == ATI_18800_1) && ((rdinx(IOAdr,0xB3) & 0x40) > 0) ||
          (MPVGA_ChipVer >= ATI_18800_1) && ((rdinx(IOAdr,0xB0) & 0x20) > 0))
        l >>= 1;
      modinx(IOAdr,0xB0,0x40,l >> 18);
      if (MPVGA_ChipVer > ATI_18800_1) modinx(IOAdr,0xA3,0x10,l >> 21);
      if (MPVGA_ChipVer >= ATI_GUP_3)  modinx(IOAdr,0xAD,0x0C,l >> 24);
      break;
    }

    case __Chips    : {
      modinx(IOAdr,0x0C,7,l >> 24);
      if ((rdinx(IOAdr,0x28) & 0x10) > 0) shft = 6;
      break;
    }

    case __Cirrus54 : {
      l = l + (l & 0x6000000);
      modinx(CRTC,0x1B,0x0D,l >> 24);
      if ((rdinx(SEQ,7) & 1) > 0) shft += 1;
      if ((rdinx(SEQ,7) & 6) == 6) shft += 1;
      break;
    }

    case __Cirrus64 : wrinx(GRC,0x7C,l >> 24); break;

    case __Compaq   : modinx(GRC,0x42,0x1C,l >> 22); break;

    case __HMC      : {
      if ((rdinx(SEQ,0xE7) & 1) > 0) l >>= 1;
      modinx(SEQ,0xED,1,l >> 24);
      break;
    }

    case __Matrox   : {
      l >>= 1;
      clrinx(CRTC,0x11,0x80);
      modinx(CRTC,8,0x60,l >> 3);
      modinx(0x3DE,0x0A,0x13,(l >> 24)+0x10);
      break;
    }

    case __MXIC     : modinx(SEQ,0xF1,3,l >> 24); break;

    case __NCR      : modinx(CRTC,0x31,0x0F,l >> 24); break;

    case __Oak      : {
      if (MPVGA_ChipVer <= OAK_083) {
	modinx(0x3DE,0x14,8,l >> 21);
	modinx(0x3DE,0x16,8,l >> 22);
      } else {
        if ((rdinx(0x3DE,0x21) & 4) > 0) l >>= 1;
        modinx(0x3DE,0x17,7,l >> 24);
      }
      break;
    }

    case __Primus   : {
      modinx(GRC,0x21,7,l >> 24);
      shft += 1;
      break;
    }

    case __Realtek  : {
      if ((rdinx(GRC,0x0C) & 0x10) != 0) l >>= 1;
      l = l + (l & 0x2000000);
      modinx(CRTC,0x19,0x50,l >> 20);
      break;
    }

    case __S3       : {
      wrinx(CRTC,0x38,0x48);
      modinx(CRTC,0x31,0x30,l >> 20);
      if (MPVGA_ChipVer > S3_924) {
        wrinx(CRTC,0x39,0xA5);
        modinx(CRTC,0x51,3,l >> 26);
        wrinx(CRTC,0x39,0x5A);
      }
      wrinx(CRTC,0x38,0);
      break;
    }

    case __Sierra   : modinx(CRTC,0x1E,0x0F,l >> 24); break;

    case __SiS      : modinx(SEQ,0x27,0x0F,l >> 24); break;

    case __Trident  : {
      wrinx(SEQ,0x0B,0);

      if ((rdinx(SEQ,0x0D) & 0x10) > 0) l >>= 1;

      if (MPVGA_ChipVer == TR_8900B || MPVGA_ChipVer == TR_8900C)
 	modinx(SEQ,0x0E,1,l >> 25);
      rdinx(SEQ,0x0B);

      modinx(CRTC,0x1E,0x20,l >> 19);

      if (MPVGA_ChipVer >= TR_9000C) modinx(CRTC,0x27,3,l >> 25);
      if (MPVGA_ChipVer >= TR_8900CL && (rdinx(GRC,0x0F) & 2) > 0) shft = 6;
      break;
    }

    case __Tseng    : {
      if (MPVGA_ChipVer == ET_3000) {
        l >>= 1;
	shft += 1;
        modinx(CRTC,0x23,2,l >> 23);
      } else {
        if (MPVGA_ChipVer == ET_4000) x = 3; else x = 0x0F;
        modinx(CRTC,0x33,x,l >> 24);
      }
      break;
    }

    case __UMC      : {
      if ((rdinx(CRTC,0x33) & 0x10) > 0) l >>= 1;
      modinx(CRTC,0x33,3,l >> 24);
      break;
    }

    case __Video7   : {
      modinx(SEQ,0xF6,0x30,l >> 20);
      if ((rdinx(SEQ,0xC8) & 0x10) > 0) shft = 6;
      break;
    }

    case __WD       : {
      modinx(GRC,0x0D,0x18,l >> 21);
      if (MPVGA_ChipVer == WD_90c33) {
	x = rdinx(CRTC,0x11);
	clrinx(CRTC,0x11,0x80);
	modinx(CRTC,0x3E,0x40,l >> 20);
	wrinx(CRTC,0x11,x);
      }
      break;
    }

    default : return;
  }

  clrinx(CRTC,0x11,0x80);
  wrinx(0x3C0,0x13,(l & 0xFF) >> shft);
  outp(0x3C0,0x33);
  wrinx(CRTC,0x0D,(l >> 8) & 0xFF);
  wrinx(CRTC,0x0C,(l >> 16) & 0xFF);

  return;
}