apps/plugins/rockboy/lcdc.c

   1 #include "rockmacros.h"
   2
   3 #include "defs.h"
   4 #include "hw.h"
   5 #include "cpu-gb.h"
   6 #include "regs.h"
   7 #include "lcd-gb.h"
   8 #include "fb.h"
   9
  10
  11 #define C (cpu.lcdc)
  12
  13
  14 /*
  15  * stat_trigger updates the STAT interrupt line to reflect whether any
  16  * of the conditions set to be tested (by bits 3-6 of R_STAT) are met.
  17  * This function should be called whenever any of the following occur:
  18  * 1) LY or LYC changes.
  19  * 2) A state transition affects the low 2 bits of R_STAT (see below).
  20  * 3) The program writes to the upper bits of R_STAT.
  21  * stat_trigger also updates bit 2 of R_STAT to reflect whether LY=LYC.
  22  */
  23
  24 void stat_trigger(void)
  25 {
  26     static const int condbits[4] = { 0x08, 0x10, 0x20, 0x00 };
  27     int flag = 0;
  28
  29     if (R_LY == R_LYC)
  30     {
  31         R_STAT |= 0x04;
  32         if (R_STAT & 0x40) flag = IF_STAT;
  33     }
  34     else R_STAT &= ~0x04;
  35
  36     if (R_STAT & condbits[R_STAT&3]) flag = IF_STAT;
  37
  38     if (!(R_LCDC & 0x80)) flag = 0;
  39
  40     hw_interrupt(flag, IF_STAT);
  41 }
  42
  43 /*
  44  * stat_change is called when a transition results in a change to the
  45  * LCD STAT condition (the low 2 bits of R_STAT).  It raises or lowers
  46  * the VBLANK interrupt line appropriately and calls stat_trigger to
  47  * update the STAT interrupt line.
  48  */
  49
  50 static void stat_change(unsigned int stat)
  51 {
  52     R_STAT = (R_STAT & 0x7C) | stat;
  53
  54     if (stat != 1) hw_interrupt(0, IF_VBLANK);
  55     /* hw_interrupt((stat == 1) ? IF_VBLANK : 0, IF_VBLANK); */
  56     stat_trigger();
  57 }
  58
  59
  60 void lcdc_change(byte b)
  61 {
  62     byte old = R_LCDC;
  63     R_LCDC = b;
  64     if ((R_LCDC ^ old) & 0x80) /* lcd on/off change */
  65     {
  66         R_LY = 0;
  67         stat_change(2);
  68         C = 40;
  69         lcd_begin();
  70     }
  71 }
  72
  73
  74 void lcdc_trans(void)
  75 {
  76     if (!(R_LCDC & 0x80))
  77     {
  78         while (C <= 0)
  79         {
  80             switch ((byte)(R_STAT & 3))
  81             {
  82             case 0:
  83             case 1:
  84                 stat_change(2);
  85                 C += 40;
  86                 break;
  87             case 2:
  88                 stat_change(3);
  89                 C += 86;
  90                 break;
  91             case 3:
  92                 stat_change(0);
  93                 if (hw.hdma & 0x80)
  94                     hw_hdma();
  95                 else
  96                     C += 102;
  97                 break;
  98             }
  99             return;
 100         }
 101     }
 102     while (C <= 0)
 103     {
 104         switch ((byte)(R_STAT & 3))
 105         {
 106         case 1:
 107             if (!(hw.ilines & IF_VBLANK))
 108             {
 109                 C += 218;
 110                 hw_interrupt(IF_VBLANK, IF_VBLANK);
 111                 break;
 112             }
 113             if (R_LY == 0)
 114             {
 115                 lcd_begin();
 116                 stat_change(2);
 117                 C += 40;
 118                 break;
 119             }
 120             else if (R_LY < 152)
 121                 C += 228;
 122             else if (R_LY == 152)
 123                 C += 28;
 124             else
 125             {
 126                 R_LY = -1;
 127                 C += 200;
 128             }
 129             R_LY++;
 130             stat_trigger();
 131             break;
 132         case 2:
 133             if (fb.enabled)
 134                 lcd_refreshline();
 135             stat_change(3);
 136             C += 86;
 137             break;
 138         case 3:
 139             stat_change(0);
 140             if (hw.hdma & 0x80)
 141                 hw_hdma();
 142             /* FIXME -- how much of the hblank does hdma use?? */
 143             /* else */
 144             C += 102;
 145             break;
 146         case 0:
 147             if (++R_LY >= 144)
 148             {
 149                 if (cpu.halt)
 150                 {
 151                     hw_interrupt(IF_VBLANK, IF_VBLANK);
 152                     C += 228;
 153                 }
 154                 else C += 10;
 155                 stat_change(1);
 156                 break;
 157             }
 158             stat_change(2);
 159             C += 40;
 160             break;
 161         }
 162     }
 163 }
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