Fix broken timer fix bug fixes

core/cpu.c

@@ -91,11 +91,6 @@
 #define CPU_XORBSU   82
 #define CPU_XORNBSU  83
 
-/* Functional operand types */
-#define CPU_LITERAL  0
-#define CPU_MEMORY   1
-#define CPU_REGISTER 2
-
 /* Bit string operations */
 #define CPU_AND_BS  0
 #define CPU_ANDN_BS 1

core/timer.c

@@ -5,6 +5,15 @@
 
 /***************************** Module Functions ******************************/
 
+/* Compute clocks until the next decrement to zero */
+static uint32_t tmrGetUntil(VB *sim) {
+    uint32_t fullTick = sim->tmr.t_clk_sel ? 400 : 2000;
+    uint32_t thisTick = sim->tmr.clocks +
+        (sim->tmr.t_clk_sel ? 0 : 400 * (4 - sim->tmr.tick20));
+    return thisTick + fullTick *
+        (sim->tmr.counter == 0 ? sim->tmr.reload : sim->tmr.counter - 1);
+}
+
 /* Update the counter to a new value */
 static void tmrUpdate(VB *sim, uint16_t value) {
     if (value == 0 && sim->tmr.counter != 0) {
@@ -23,10 +32,6 @@ static void tmrUpdate(VB *sim, uint16_t value) {
 /* Process component */
 static void tmrEmulate(VB *sim, uint32_t clocks) {
 
-    /* Timer is disabled */
-    if (!sim->tmr.t_enb)
-        return;
-
     /* Process all clocks */
     for (;;) {
 
@@ -40,13 +45,20 @@ static void tmrEmulate(VB *sim, uint32_t clocks) {
         /* Advance forward the component's number of clocks */
         clocks          -= sim->tmr.clocks;
         sim->tmr.until  -= sim->tmr.clocks;
-        sim->tmr.clocks = sim->tmr.t_clk_sel ? 400 : 2000;
+        sim->tmr.clocks  = 400;
+        sim->tmr.tick20 += sim->tmr.tick20 == 4 ? -4 : 1;
+
+        /* Do not decrement counter */
+        if (
+            !sim->tmr.t_enb ||
+            (!sim->tmr.t_clk_sel && sim->tmr.tick20 != 0)
+        ) continue;
 
         /* Advance to the next counter value */
         tmrUpdate(sim, sim->tmr.counter == 0 ?
             sim->tmr.reload : sim->tmr.counter - 1);
         if (sim->tmr.counter == 0)
-            sim->tmr.until = sim->tmr.clocks * ((uint32_t)sim->tmr.reload + 1);
+            sim->tmr.until = tmrGetUntil(sim);
     }
 
 }
@@ -71,8 +83,10 @@ static void tmrReset(VB *sim) {
     sim->tmr.z_stat    = 0;
 
     /* Other */
+    sim->tmr.clocks  = 400;
     sim->tmr.counter = 0xFFFF;
     sim->tmr.reload  = 0x0000;
+    sim->tmr.tick20  = 0;
 }
 
 /* Determine how many clocks are guaranteed to process */
@@ -88,14 +102,27 @@ static void tmrWriteControl(VB *sim, uint8_t value) {
     if (
         (value & 0x04) && /* Z-Stat-Clr */
         (
-            sim->tmr.counter != 0 ||
-            !sim->tmr.t_enb
+            !sim->tmr.t_enb ||
+            (
+                sim->tmr.counter != 0 &&
+                !(value & 0x01) /* T-Enb */
+            )
         )
     ) {
         sim->tmr.z_stat = sim->tmr.counter != 0;
         sim->cpu.irq   &= ~0x0002;
     }
 
+    /* Hardware bug: decrement on switch to 20us mode */
+    if (
+        !sim->tmr.t_clk_sel &&
+        (value & 0x10)      && /* T-Clk-Sel */
+        sim->tmr.tick20 != 4
+    ) {
+        tmrUpdate(sim, sim->tmr.counter == 0 ?
+            sim->tmr.reload : sim->tmr.counter - 1);
+    }
+
     /* Parse fields */
     sim->tmr.t_clk_sel = value >> 4 & 1;
     sim->tmr.tim_z_int = value >> 3 & 1;
@@ -105,10 +132,8 @@ static void tmrWriteControl(VB *sim, uint8_t value) {
     if (!sim->tmr.tim_z_int)
         sim->cpu.irq &= ~0x0002;
 
-    /* Configure countdowns */
-    sim->tmr.clocks = sim->tmr.t_clk_sel ? 400 : 2000;
-    sim->tmr.until  = sim->tmr.clocks * (sim->tmr.counter == 0 ?
-        (uint32_t) sim->tmr.reload + 1 : sim->tmr.counter);
+    /* Configure state */
+    sim->tmr.until = tmrGetUntil(sim);
 
     /* TODO: Will Z-Stat raise an interrupt when Tim-Z-Int is set? */
 }
@@ -117,12 +142,14 @@ static void tmrWriteControl(VB *sim, uint8_t value) {
 static void tmrWriteHigh(VB *sim, uint8_t value) {
     sim->tmr.reload = (uint16_t) value << 8 | (sim->tmr.reload & 0x00FF);
     tmrUpdate(sim, sim->tmr.reload);
+    sim->tmr.until  = tmrGetUntil(sim);
 }
 
 /* Write to the low data register */
 static void tmrWriteLow(VB *sim, uint8_t value) {
     sim->tmr.reload = (sim->tmr.reload & 0xFF00) | value;
     tmrUpdate(sim, sim->tmr.reload);
+    sim->tmr.until  = tmrGetUntil(sim);
 }
 
 

core/vb.c

@@ -8,8 +8,11 @@
 
 /*********************************** Types ***********************************/
 
-/* Output image */
-typedef uint8_t Pixels[2][384*224];
+/* VIP BG map cell */
+typedef struct {
+    uint8_t *palette; /* Points to a VB.vip.gplt */
+    uint8_t *pixels;  /* Points to a VB.vip.characters */
+} Cell;
 
 /* VSU channel */
 typedef struct {
@@ -64,9 +67,58 @@ typedef struct {
     } wave;
 
     /* Other state */
-    uint32_t clocks; /* Clocks until next sample */
+    uint32_t clocks;  /* Clocks until next wave or noise sample */
+    uint8_t  freqmod; /* Frequency modifications are active */
+    uint32_t until;   /* Clocks until channel component update */
 } Channel;
 
+/* VIP character (hflp << 1 | vflp) */
+typedef uint8_t Character[4][64];
+
+/* VIP object */
+typedef struct {
+    Cell    cell; /* BG map-like attributes */
+    int16_t jp;   /* Parallax */
+    int16_t jx;   /* Screen base X */
+    int16_t jy;   /* Screen Y */
+    uint8_t lron; /* Visible in left and right images */
+} Object;
+
+/* Output image */
+typedef uint8_t Pixels[2][384*224];
+
+/* VIP world */
+typedef struct {
+
+    /* Attributes */
+    uint8_t  bgm;       /* Mode */
+    uint8_t  end;       /* Control world */
+    int16_t  gp;        /* World parallax */
+    int16_t  gx;        /* World base X */
+    int16_t  gy;        /* World Y */
+    int16_t  mx;        /* Scroll base X */
+    int16_t  mp;        /* Scroll parallax */
+    int16_t  my;        /* Scroll Y */
+    uint8_t  over;      /* Use overplane */
+    Cell    *overplane; /* Overplane cell */
+
+    /* Non-attributes */
+    Cell    *bg[64];    /* Background arrangement */
+    int32_t  bgHeight;  /* Height of background in pixels */
+    uint32_t bgMaskX;   /* Horizontal background mask */
+    uint32_t bgMaskY;   /* Vertical background mask */
+    uint32_t bgShift;   /* Bits to shift when selecting a BG map */
+    int32_t  bgWidth;   /* Width of background in pixels */
+    uint32_t hAffine;   /* H for affine mode */
+    uint32_t hNaffine;  /* H for not affine mode */
+    uint32_t height;    /* Height of world in pixels */
+    uint8_t  lron;      /* Visible in left and right images */
+    uint32_t paramBase; /* H-bias and affine parameter address */
+    uint32_t wAffine;   /* W for affine mode */
+    uint32_t wNaffine;  /* W for not affine mode */
+    uint32_t width;     /* Width of world in pixels */
+} World;
+
 /* Simulation state */
 struct VB {
 
@@ -199,6 +251,7 @@ struct VB {
         uint32_t clocks;  /* Master clocks to wait */
         uint16_t counter; /* Current counter value */
         uint16_t reload;  /* Reload counter value */
+        uint8_t  tick20;  /* Current 20-microsecond tick */
         uint32_t until;   /* Clocks until interrupt condition */
     } tmr;
 
@@ -278,7 +331,11 @@ struct VB {
         Pixels   shadow;            /* Drawing shadow image, column-major */
 
         /* Other state */
+        Cell      cells[0x10000];   /* Pre-computed BG map attributes */
+        Character characters[2048]; /* Pre-computed character pixels */
+        Object    objects[1024];    /* Pre-computed object attributes */
         uint8_t   ram[0x40000];     /* Video memory */
+        World     worlds[32];       /* Pre-computed world attributes */
     } vip;
 
     /* VSU */
@@ -643,6 +700,7 @@ VBAPI vbOnWrite vbGetWriteCallback(VB *sim) {
 VBAPI VB* vbInit(VB *sim) {
     sim->cart.ram        = NULL;
     sim->cart.rom        = NULL;
+    sim->ph.enabled      = 0;
     sim->vsu.out.samples = NULL;
     sim->onExecute       = NULL;
     sim->onFetch         = NULL;
@@ -652,7 +710,7 @@ VBAPI VB* vbInit(VB *sim) {
     sim->onSamples       = NULL;
     sim->onWrite         = NULL;
     sim->peer            = NULL;
-    sim->ph.enabled      = 0;
+    sim->tag             = NULL;
     vbReset(sim);
     return sim;
 }
@@ -774,6 +832,8 @@ VBAPI int vbSetOption(VB *sim, int key, int value) {
 VBAPI void vbSetPeer(VB *sim, VB *peer) {
     if (sim->peer == peer)
         return;
+    if (sim->peer != NULL)
+        sim->peer->peer = NULL;
     sim->peer = peer;
     if (peer == NULL)
         return;
@@ -784,6 +844,7 @@ VBAPI void vbSetPeer(VB *sim, VB *peer) {
 
 /* Specify a new value for the program counter */
 VBAPI uint32_t vbSetProgramCounter(VB *sim, uint32_t value) {
+    sim->cpu.clocks    = 0;
     sim->cpu.operation = CPU_FETCH;
     sim->cpu.pc        = sim->cpu.nextPC = value & 0xFFFFFFFE;
     sim->cpu.step      = 0;

core/vip.c

@@ -56,37 +56,18 @@ static const uint8_t BRIGHT8[] = {
 
 /*********************************** Types ***********************************/
 
-/* World attribtues per eye */
+/* Intersection of the screen and a world rectangle */
 typedef struct {
-    int32_t bp;          /* BG source parallax */
-    int32_t left, right; /* Window bounds */
-    int32_t wx;          /* World horizontal position */
-} EyeAttribs;
-
-/* Parsed world attributes */
-typedef struct {
-    int32_t  base;        /* Base BG map index */
-    uint8_t *bg;          /* Background template */
-    int32_t  bgm;         /* World type */
-    int32_t  bgw, bgh;    /* Background dimension masks */
-    int32_t  bottom, top; /* Window bounds */
-    int32_t  gx, gp, gy;  /* World screen position */
-    int32_t  mx, mp, my;  /* Background scroll */
-    uint8_t *over;        /* Overplane character */
-    uint32_t params;      /* Line parameters address */
-    int32_t  scx, scy;    /* Background dimensions */
-    int32_t  w, h;        /* Window size */
-} WorldAttribs;
+    int32_t x1; /* Left edge inclusive */
+    int32_t x2; /* Right edge exclusive */
+    int32_t y1; /* Top edge inclusive */
+    int32_t y2; /* Bottom edge exclusive */
+} Window;
 
 
 
 /***************************** Module Functions ******************************/
 
-/* Retrieve a pointer to character data in host memory */
-static uint8_t* vipCharacter(VB *sim, uint32_t c) {
-    return &sim->vip.ram[0x06000 | (c << 6 & 0x18000) | (c << 4 & 0x01FF0)];
-}
-
 /* Read a palette */
 static int32_t vipReadPalette(uint8_t *entries) {
     return entries[3] << 6 | entries[2] << 4 | entries[1] << 2;
@@ -244,6 +225,178 @@ static int32_t vipReadIO(VB *sim, uint32_t address, int type) {
     value;
 }
 
+/* Write into BG map cell memory */
+static void vipWriteCell(VB *sim, uint32_t offset, int type, int32_t value) {
+    Cell *cell;
+
+    /* Adjustments for byte and word writes */
+    switch (type) {
+        case VB_S8:
+        case VB_U8:
+            value = offset & 1 ?
+                value << 8 |           sim->vip.ram[0x20001 ^ offset] :
+                value      | (int32_t) sim->vip.ram[0x20001 | offset] << 8
+            ;
+            break;
+        case VB_S32:
+            vipWriteCell(sim, offset + 2, VB_U16, value >> 16);
+            break;
+    }
+
+    /* Update pixel pointer */
+    cell          = &sim->vip.cells[offset >> 1];
+    cell->palette = sim->vip.gplt[value >> 14 & 3];
+    cell->pixels  = sim->vip.characters[value & 0x07FF][value >> 12 & 3];
+}
+
+/* Write into character memory */
+static void vipWriteChr(VB *sim, uint32_t offset, int type, int32_t value) {
+    Character *chr;        /* Pixel state */
+    int        b, l, r, t; /* Pixel bounds */
+    int        x, y, X, Y; /* Iterators */
+
+    /* Byte advance by data type */
+    static const uint8_t HORZ[] = { 4, 4, 8, 8,  8 };
+    static const uint8_t VERT[] = { 8, 8, 8, 8, 16 };
+
+    /* Working variables */
+    chr = &sim->vip.characters[offset >> 4];
+    l   = (offset & 0x1) << 2;
+    t   = (offset & 0xE) << 2;
+    r   = l + HORZ[type];
+    b   = t + VERT[type];
+
+    /* Process all pixels */
+    for (y = t, Y = 56 - y; y < b; y += 8, Y -= 8)
+    for (x = l, X =  7 - x; x < r; x += 1, X -= 1, value >>= 2) {
+        (*chr)[0][y | x] = (*chr)[1][Y | x] =
+        (*chr)[2][y | X] = (*chr)[3][Y | X] = value & 3;
+    }
+
+}
+
+/* Write into object attribute memory */
+static void vipWriteObject(VB *sim, uint32_t offset, int type, int32_t value) {
+    Object *obj; /* Object state */
+
+    /* Adjustments for byte and word writes */
+    switch (type) {
+        case VB_S8:
+        case VB_U8:
+            value = offset & 1 ?
+                value << 8 |           sim->vip.ram[0x3E001 ^ offset] :
+                value      | (int32_t) sim->vip.ram[0x3E001 | offset] << 8
+            ;
+            break;
+        case VB_S32:
+            vipWriteObject(sim, offset + 2, VB_U16, value >> 16);
+            break;
+    }
+
+    /* Processing by offset */
+    obj = &sim->vip.objects[offset >> 3];
+    switch (offset >> 1 & 3) {
+        case 0: obj->jx = SignExtend(value, 10); break;
+        case 1:
+            obj->jp   = SignExtend(value, 10);
+            obj->lron = value >> 14 & 3;
+            break;
+        case 2:
+            value = (int8_t) value;
+            obj->jy = value > -8 ? value : value & 0xFF;
+            break;
+        case 3:
+            obj->cell.palette = sim->vip.jplt[value >> 14 & 3];
+            obj->cell.pixels  =
+                sim->vip.characters[value & 0x07FF][value >> 12 & 3];
+    }
+
+}
+
+/* Write into world attribute memory */
+static void vipWriteWorld(VB *sim, uint32_t offset, int type, int32_t value) {
+    uint32_t base;  /* Base BG map index */
+    uint8_t *bg;    /* Background template */
+    uint32_t count; /* Number of BG maps in background */
+    World   *world; /* World state */
+    uint32_t z;     /* Iterator */
+
+    /* Adjustments for byte and word writes */
+    switch (type) {
+        case VB_S8:
+        case VB_U8:
+            value = offset & 1 ?
+                value << 8 |           sim->vip.ram[0x3D801 ^ offset] :
+                value      | (int32_t) sim->vip.ram[0x3D801 | offset] << 8
+            ;
+            break;
+        case VB_S32:
+            vipWriteWorld(sim, offset + 2, VB_U16, value >> 16);
+            break;
+    }
+
+    /* Processing by offset */
+    world = &sim->vip.worlds[offset >> 5];
+    switch (offset >> 1 & 15) {
+        case 0:
+
+            /* Parse attributes */
+            world->lron = value >> 14 & 3;
+            world->bgm  = value >> 12 & 3;
+            world->over = value >>  7 & 1;
+            world->end  = value >>  6 & 1;
+
+            /* Update background fields */
+            z               = value >> 10 & 3;
+            world->bgMaskX  =  (1 << z) - 1;
+            world->bgWidth  = 512 << z;
+            world->bgShift  = z;
+            z               = value >>  8 & 3;
+            world->bgMaskY  =  (1 << z) - 1;
+            world->bgHeight = 512 << z;
+
+            /* Update world dimensions */
+            if (world->bgm != 2) {
+                world->height = world->hNaffine;
+                world->width  = world->wNaffine;
+            } else {
+                world->height = world->hAffine;
+                world->width  = world->wAffine;
+            }
+
+            /* Update background arrangement */
+            count = (world->bgMaskX + 1) * (world->bgMaskY + 1);
+            base  = value & 15 & ~(count > 8 ? 7 : count - 1);
+            bg    = (uint8_t *) BG_TEMPLATES[value >> 8 & 15];
+            for (z = 0; z < count; z++)
+                world->bg[z] = &sim->vip.cells[(base + bg[z]) << 12];
+            break;
+
+        case 1: world->gx = SignExtend(value, 10); break;
+        case 2: world->gp = SignExtend(value, 10); break;
+        case 3: world->gy = (int16_t) value;       break;
+        case 4: world->mx = SignExtend(value, 13); break;
+        case 5: world->mp = SignExtend(value, 15); break;
+        case 6: world->my = SignExtend(value, 13); break;
+        case 7: /* W */
+            value = SignExtend(value, 13) + 1;
+            world->wNaffine = value < 0 ? 0 : value;
+            value = SignExtend(value, 10) + 1;
+            world->wAffine  = value < 0 ? 0 : value;
+            world->width = world->bgm != 2 ? world->wNaffine : world->wAffine;
+            break;
+        case 8: /* H */
+            value = (int16_t) value + 1;
+            world->hNaffine = value < 8 ? 8 : value;
+            world->hAffine  = value < 0 ? 0 : value;
+            world->height = world->bgm != 2 ? world->hNaffine : world->hAffine;
+            break;
+        case  9: world->paramBase = 0x20000|(uint32_t)(uint16_t)value<<1;break;
+        case 10: world->overplane = &sim->vip.cells[(uint16_t) value];   break;
+    }
+
+}
+
 /* Write a typed value to an I/O register */
 static void vipWriteIO(
     VB *sim, uint32_t address, int type, int32_t value, int debug) {
@@ -328,10 +481,12 @@ static void vipWriteIO(
             break;
 
         case 0x5F830>>1: /* CTA */
+            if (debug) {
                 if ((mask & 0xFF00) == 0)
                     sim->vip.cta.cta_r = value >> 8;
                 if ((mask & 0x00FF) == 0)
                     sim->vip.cta.cta_l = value;
+            }
             break;
 
         case 0x5F842>>1: /* XPCTRL */
@@ -627,313 +782,354 @@ static int vipEmulateDisplay(VB *sim, uint32_t clocks) {
 
 /****************************** Pixel Processor ******************************/
 
-/* Parse eye attributes and test window bounds */
-static int vipParseEye(WorldAttribs *wttr, EyeAttribs *ettr, int eye) {
+/* Draw a cell into shadow memory */
+static void vipDrawCell(uint8_t *shadow, Window *wnd,
+    Cell *cell, int32_t x, int32_t y) {
+    uint8_t *col, *row;          /* Output pixel */
+    uint8_t  pixel;              /* Character pixel value */
+    int32_t  px1, px2, py1, py2; /* Pixel bounds in cell */
+    int32_t  px, py;             /* Pixel origin in cell */
 
-    /* Validate the world isn't right of frame */
-    ettr->wx = wttr->gx - (eye == 0 ? wttr->gp : -wttr->gp);
-    if (ettr->wx > 383)
-        return 1;
-    ettr->left = ettr->wx < 0 ? 0 : ettr->wx;
+    /* Identify the visible pixels */
+    py1 = y     > wnd->y1 ? y     : wnd->y1;
+    py2 = y + 8 < wnd->y2 ? y + 8 : wnd->y2;
+    px1 = x     > wnd->x1 ? x     : wnd->x1;
+    px2 = x + 8 < wnd->x2 ? x + 8 : wnd->x2;
 
-    /* Validate the world isn't left of frame */
-    ettr->right = ettr->wx + wttr->w - 1;
-    if (ettr->right < 0)
-        return 1;
-    if (ettr->right > 383)
-        ettr->right = 383;
+    /* Process all columns of pixels */
+    col = &shadow[px1 * 224 + py1];
+    for (px = px1; px < px2; px++, col += 224)
+    for (py = py1, row = col; py < py2; py++, row++) {
+        pixel = cell->pixels[(py - y) << 3 | (px - x)];
+        if (pixel != 0)
+            *row = cell->palette[pixel];
+    }
 
-    /* BG source parallax */
-    if (wttr->bgm != 2)
-        ettr->bp = eye == 0 ? -wttr->mp : wttr->mp;
-
-    return 0;
 }
 
-/* Parse world attributes and test window bounds */
-static int vipParseWorld(VB*sim,uint8_t*world,uint16_t bits,WorldAttribs*attr){
-    int32_t z; /* Scratch */
+/* Draw a BG map into shadow memory */
+static void vipDrawBGMap(uint8_t *shadow, Window *wnd,
+    uint8_t over, Cell *map, int32_t x, int32_t y) {
+    Cell   *col, *row;          /* Source cell */
+    int32_t cx1, cx2, cy1, cy2; /* Cell bounds in BG map pixels */
+    int32_t cx, cy;             /* Cell origin in BG map pixels */
 
-    /* Validate the world isn't below the frame */
-    attr->gy = busReadBuffer(world + 6, VB_S16);
-    if (attr->gy > 223)
-        return 1;
+    /* Identify the visible cells */
+    cy1 = (wnd->y1-y  ) & ~7; if (cy1 < 0) cy1 = 0; if (cy1 > 512) cy1 = 512;
+    cy2 = (wnd->y2-y+7) & ~7; if (cy2 < 0) cy2 = 0; if (cy2 > 512) cy2 = 512;
+    cx1 = (wnd->x1-x  ) & ~7; if (cx1 < 0) cx1 = 0; if (cx1 > 512) cx1 = 512;
+    cx2 = (wnd->x2-x+7) & ~7; if (cx2 < 0) cx2 = 0; if (cx2 > 512) cx2 = 512;
 
-    /* Validate the world isn't above the frame, and height is positive */
-    attr->bgm = bits >> 12 & 3;
-    attr->h   = busReadBuffer(world + 16, VB_S16) + 1;
-    z         = attr->bgm == 2 ? 0 : 8;
-    if (attr->h < z)
-        attr->h = z;
-    if (attr->h == 0)
-        return 1;
-    attr->bottom = attr->gy + attr->h - 1;
-    attr->top    = (int32_t) sim->vip.xp.sbcount << 3;
-    if (attr->bottom < attr->top)
-        return 1;
-    if (attr->bottom > 223)
-        attr->bottom = 223;
-    if (attr->top < attr->gy)
-        attr->top = attr->gy;
-
-    /* Validate width is positive */
-    attr->w = SignExtend(busReadBuffer(world + 14, VB_U16),
-        attr->bgm == 2 ? 10 : 13) + 1;
-    if (attr->w < 1)
-        return 1;
-
-    /* Parse attributes */
-    attr->bg   = (uint8_t *) BG_TEMPLATES[bits >> 8 & 15];
-    attr->gx   = SignExtend(busReadBuffer(world + 2, VB_U16), 10);
-    attr->gp   = SignExtend(busReadBuffer(world + 4, VB_U16), 10);
-    attr->over = (bits & 0x0080) == 0 ? NULL :
-        &sim->vip.ram[0x00020000 | busReadBuffer(world + 10, VB_U16) << 1];
-    attr->scx  = bits >> 10 & 3;
-    attr->scy  = bits >>  8 & 3;
-    attr->bgw  = (1 << attr->scx) - 1;
-    attr->bgh  = (1 << attr->scy) - 1;
-    z = attr->scx + attr->scy;
-    attr->base = bits & 15 & ~((1 << (z < 3 ? z : 3)) - 1);
-    if (attr->bgm != 2) {
-        attr->mx = SignExtend(busReadBuffer(world +  8, VB_U16), 13);
-        attr->mp = SignExtend(busReadBuffer(world + 10, VB_U16), 15);
-        attr->my = SignExtend(busReadBuffer(world + 12, VB_U16), 13);
-    }
-    if (attr->bgm != 0) {
-        attr->params =
-            0x20000 +
-            (attr->top - attr->gy) * (attr->bgm == 1 ? 4 : 16) +
-            ((uint32_t) busReadBuffer(world + 18, VB_U16) << 1)
-        ;
+    /* Process all cells as overplane */
+    if (over) {
+        for (cy = cy1; cy < cy2; cy += 8)
+        for (cx = cx1; cx < cx2; cx += 8)
+            vipDrawCell(shadow, wnd, map, x + cx, y + cy);
+        return;
     }
 
-    return 0;
+    /* Process all cells normally */
+    row = &map[cy1 << 3 | cx1 >> 3];
+    for (cy = cy1           ; cy < cy2; cy += 8, row += 64)
+    for (cx = cx1, col = row; cx < cx2; cx += 8, col++)
+        vipDrawCell(shadow, wnd, col, x + cx, y + cy);
+}
+
+/* Draw a background into shadow memory */
+static void vipDrawBackground(uint8_t *shadow, Window *wnd,
+    World *world, int32_t x, int32_t y) {
+    int32_t bx1, bx2, by1, by2; /* BG map bounds in background pixels */
+    int32_t bx, by;             /* BG map origin in background pixels */
+
+    /* Identify the visible BG maps */
+    by1 = (wnd->y1 - y    ) & ~511;
+    by2 = (wnd->y2 - y - 1) & ~511;
+    bx1 = (wnd->x1 - x    ) & ~511;
+    bx2 = (wnd->x2 - x - 1) & ~511;
+
+    /* Process all rows of BG maps */
+    for (by = by1; by <= by2; by += 512) {
+
+        /* Row is out of bounds */
+        if (world->over && (by < 0 || by >= world->bgHeight)) {
+            for (bx = bx1; bx <= bx2; bx++)
+                vipDrawBGMap(shadow, wnd, 1, world->overplane, x + bx, y + by);
+            continue;
+        }
+
+        /* Process all columns of BG maps */
+        for (bx = bx1; bx <= bx2; bx += 512) {
+
+            /* Column is out of bounds */
+            if (world->over && (bx < 0 || bx >= world->bgWidth)) {
+                vipDrawBGMap(shadow, wnd, 1, world->overplane, x + bx, y + by);
+                continue;
+            }
+
+            /* Column is in bounds */
+            vipDrawBGMap(shadow, wnd, 0, world->bg[
+                (by >> 9 & world->bgMaskY) << world->bgShift |
+                (bx >> 9 & world->bgMaskX)
+            ], x + bx, y + by);
+        }
+
+    }
+
+}
+
+/* Draw a Normal world into shadow memory */
+static void vipDrawNormal(VB *sim, World *world) {
+    int32_t  mx, my; /* Background origin */
+    Window   wnd;    /* Window bounds in pixels */
+    int      i;      /* Iterator */
+
+    /* No visible content */
+    if (world->width == 0)
+        return;
+
+    /* Vertical window bounds */
+    wnd.y1 = (int32_t) sim->vip.xp.sbcount << 3;
+    if (world->gy > wnd.y1)
+        wnd.y1 = world->gy;
+    if (wnd.y1 >= 224)
+        return;
+    wnd.y2 = world->gy + world->height;
+    if (wnd.y2 <= 0)
+        return;
+    my = world->gy - world->my;
+    if (wnd.y1 < 0)
+        wnd.y1 = 0;
+    if (wnd.y2 > 224)
+        wnd.y2 = 224;
+
+    /* Process both eyes */
+    for (i = 0; i < 2; i++) {
+
+        /* Check visibility */
+        if (!(world->lron >> (i ^ 1) & 1))
+            continue;
+
+        /* Horizontal window bounds */
+        wnd.x1 = world->gx + (i == 0 ? -world->gp : world->gp);
+        if (wnd.x1 >= 384)
+            continue;
+        wnd.x2 = wnd.x1 + world->width;
+        if (wnd.x2 <= 0)
+            continue;
+        mx = wnd.x1 - world->mx - (i == 0 ? -world->mp : world->mp);
+        if (wnd.x1 < 0)
+            wnd.x1 = 0;
+        if (wnd.x2 > 384)
+            wnd.x2 = 384;
+
+        /* Draw the background into the window */
+        vipDrawBackground(sim->vip.shadow[i], &wnd, world, mx, my);
+    }
+
+}
+
+/* Draw an H-bias world into shadow memory */
+static void vipDrawHBias(VB *sim, World *world) {
+    int32_t  mx, my; /* Background origin */
+    uint8_t *param;  /* World parameter memory */
+    Window   wnd;    /* Window bounds in pixels */
+    int32_t  y1, y2; /* Vertical window bounds */
+    int      i, y;   /* Iterators */
+
+    /* No visible content */
+    if (world->width == 0)
+        return;
+
+    /* Vertical window bounds */
+    y1 = (int32_t) sim->vip.xp.sbcount << 3;
+    if (world->gy > y1)
+        y1 = world->gy;
+    if (y1 >= 224)
+        return;
+    y2 = world->gy + world->height;
+    if (y2 <= 0)
+        return;
+    my = world->gy - world->my;
+    if (y1 < 0)
+        y1 = 0;
+    if (y2 > 224)
+        y2 = 224;
+
+    /* Process both eyes */
+    for (i = 0; i < 2; i++) {
+
+        /* Check visibility */
+        if (!(world->lron >> (i ^ 1) & 1))
+            continue;
+
+        /* Horizontal window bounds */
+        wnd.x1 = world->gx + (i == 0 ? -world->gp : world->gp);
+        if (wnd.x1 >= 384)
+            continue;
+        wnd.x2 = wnd.x1 + world->width;
+        if (wnd.x2 <= 0)
+            continue;
+        mx = wnd.x1 - world->mx - (i == 0 ? -world->mp : world->mp);
+        if (wnd.x1 < 0)
+            wnd.x1 = 0;
+        if (wnd.x2 > 384)
+            wnd.x2 = 384;
+
+        /* Process all visible lines */
+        param = &sim->vip.ram[world->paramBase +
+            ((y1 - world->gy) << 2) + (i << 1)];
+        for (y = y1; y < y2; y++, param += 2) {
+
+            /* Configure window bounds */
+            wnd.y1 = y;
+            wnd.y2 = y + 1;
+
+            /* Draw the background into the window */
+            vipDrawBackground(sim->vip.shadow[i], &wnd, world,
+                mx + busReadBuffer(param, VB_S16), my);
+        }
+
+    }
+
+}
+
+/* Draw an Affine world into shadow memory */
+static void vipDrawAffine(VB *sim, World *world) {
+    Cell    *cell;               /* Source cell */
+    uint8_t *col, *row;          /* Output pixel */
+    uint8_t  pixel;              /* Character pixel value */
+    uint8_t *param;              /* World parameter memory */
+    int32_t  px, py;             /* Pixel source coordinates */
+    int32_t  dx, dy, mp, mx, my; /* Affine parameters */
+    int32_t  wx;                 /* Base world X coordinate */
+    int32_t  x1, x2, y1, y2;     /* Window bounds */
+    int      i, x, y;            /* Iterators */
+
+    /* No visible content */
+    if (world->width == 0 || world->height == 0)
+        return;
+
+    /* Vertical window bounds */
+    y1 = (int32_t) sim->vip.xp.sbcount << 3;
+    if (world->gy > y1)
+        y1 = world->gy;
+    if (y1 >= 224)
+        return;
+    y2 = world->gy + world->height;
+    if (y2 <= 0)
+        return;
+    if (y1 < 0)
+        y1 = 0;
+    if (y2 > 224)
+        y2 = 224;
+
+    /* Process both eyes */
+    for (i = 0; i < 2; i++) {
+
+        /* Check visibility */
+        if (!(world->lron >> (i ^ 1) & 1))
+            continue;
+
+        /* Horizontal window bounds */
+        x1 = world->gx + (i == 0 ? -world->gp : world->gp);
+        if (x1 >= 384)
+            continue;
+        x2 = x1 + world->width;
+        if (x2 <= 0)
+            continue;
+        wx = x1;
+        if (x1 < 0)
+            x1 = 0;
+        if (x2 > 384)
+            x2 = 384;
+        wx = x1 - wx;
+
+        /* Process all visible rows */
+        param = &sim->vip.ram[world->paramBase | (y1 - world->gy) << 4];
+        row   = &sim->vip.shadow[i][x1 * 224 + y1];
+        for (y = y1; y < y2; y++, param += 16, row++) {
+
+            /* Parse line parameters */
+            mx = (int32_t) busReadBuffer(param + 0, VB_S16) << 6;
+            mp = (int32_t) busReadBuffer(param + 2, VB_S16);
+            my = (int32_t) busReadBuffer(param + 4, VB_S16) << 6;
+            dx = (int32_t) busReadBuffer(param + 6, VB_S16);
+            dy = (int32_t) busReadBuffer(param + 8, VB_S16);
+
+            /* Adjust left-edge parameters */
+            if ((mp < 0) ^ i) {
+                mx += dx * (wx - mp);
+                my += dy * (wx - mp);
+            } else {
+                mx += dx * wx;
+                my += dy * wx;
+            }
+
+            /* Process all visible columns */
+            col = row;
+            for (x = x1; x < x2; x++, mx += dx, my += dy, col += 224) {
+                px = (int16_t) (mx >> 9);
+                py = (int16_t) (my >> 9);
+
+                /* Overplane */
+                if (world->over && (
+                    px < 0 || px >= world->bgWidth ||
+                    py < 0 || py >= world->bgHeight
+                )) cell = world->overplane;
+
+                /* Regular */
+                else cell = &world->bg[
+                    (py >> 9 & world->bgMaskY) << world->bgShift |
+                    (px >> 9 & world->bgMaskX)
+                ][(py << 3 & 0xFC0) | (px >> 3 & 63)];
+
+                /* Sample the pixel */
+                pixel = cell->pixels[(py & 7) << 3 | (px & 7)];
+                if (pixel != 0)
+                    *col = cell->palette[pixel];
+
+            } /* x */
+
+        } /* y */
+
+    } /* i */
+
 }
 
 /* Draw an object group into shadow memory */
 static void vipDrawObjects(VB *sim, int group) {
-    uint8_t *dest;       /* Pointer to object position in shadow memory */
-    int      fx;         /* Output horizontal position */
-    int      fy;         /* Output vertical position */
-    uint8_t *obj;        /* Pointer to object attributes in host memory */
-    int32_t  ox;         /* Eye horizontal position */
-    int      pixel;      /* Character input pixel */
-    int      start;      /* Index of first object in group */
-    int      stop;       /* Index of last object in group */
-    int      sx;         /* Input horizontal position */
-    int      sy;         /* Input vertical position */
-    int32_t  top;        /* Window boundary */
-    int      i, o, x, y; /* Iterators */
+    Object *obj;   /* Object state */
+    int     start; /* First object in the group */
+    int     stop;  /* Last object in the group */
+    Window  wnd;   /* Window bounds in pixels */
+    int     i, o;  /* Iterators */
 
-    /* Object attributes */
-    uint32_t attr1;      /* Attribute bits */
-    uint32_t attr2;      /* Attribute bits */
-    int      jhflp;      /* Is flipped horizontally */
-    int32_t  jp;         /* Stereo parallax */
-    int      jvflp;      /* Is flipped vetically */
-    int32_t  jx;         /* Base horizontal position */
-    int32_t  jy;         /* Vertical position */
-    uint8_t *plt;        /* Palette */
-    uint8_t *src;        /* Pointer to character source data in host memory */
+    /* Establish the viewing window */
+    wnd.x1 = 0;
+    wnd.y1 = (int32_t) sim->vip.xp.sbcount << 3;
+    wnd.x2 = 384;
+    wnd.y2 = 224;
 
     /* Process all objects in the group */
     start = group == 0 ? 0 : (sim->vip.spt[group - 1] + 1) & 1023;
     stop  = sim->vip.spt[group];
-    top   = (int32_t) sim->vip.xp.sbcount << 3;
     for (o = stop; o != -1; o = o == start ? -1 : (o - 1) & 1023) {
-        obj = &sim->vip.ram[0x3E000 | o << 3];
-
-        /* Validate object is enabled */
-        attr1 = busReadBuffer(obj + 2, VB_U16);
-        if ((attr1 & 0xC000) == 0) /* JLON, JRON */
-            continue;
-
-        /* Validate Y position */
-        jy = (int8_t) obj[4];
-        if (jy < 7)
-            jy &= 0xFF;
-        if (jy < top - 7 || jy > 223)
-            continue;
-
-        /* Parse attributes */
-        jx    = SignExtend(busReadBuffer(obj, VB_U16), 10);
-        jp    = SignExtend(attr1, 10);
-        attr2 = busReadBuffer(obj + 6, VB_U16);
-        jhflp = attr2 >> 13 & 1;
-        jvflp = attr2 >> 12 & 1;
-
-        /* Locate palette and character state in host memory */
-        plt = sim->vip.jplt[attr2 >> 14];
-        src = vipCharacter(sim, attr2); 
-
-        /* Draw the character */
+        obj = &sim->vip.objects[o];
         for (i = 0; i < 2; i++) {
-            if ((attr1 >> (15 - i) & 1) == 0) /* J*ON */
+            if (!(obj->lron >> (i ^ 1) & 1))
                 continue;
-            ox   = jx - (i == 0 ? jp : -jp);
-            dest = &sim->vip.shadow[i][ox * 224 + jy];
-
-            /* Draw all columns */
-            for (x = 0; x < 8; x++, dest += 224) {
-                fx = ox + x;
-                if (fx < 0 || fx > 383)
-                    continue;
-                sx = jhflp ? 7 - x : x;
-
-                /* Draw all rows */
-                for (y = 0; y < 8; y++) {
-                    fy = jy + y;
-                    if (fy < top || fy > 223)
-                        continue;
-                    sy    = jvflp ? 7 - y : y;
-                    pixel = src[sy << 1 | sx >> 2] >> ((sx & 3) << 1) & 3;
-                    if (pixel != 0)
-                        dest[y] = plt[pixel]; /* TODO: Research clocks */
-                } /* y */
-
-            } /* x */
-
-        } /* i */
-
+            vipDrawCell(sim->vip.shadow[i], &wnd, &obj->cell,
+                obj->jx + (i == 0 ? -obj->jp : obj->jp), obj->jy);
         }
-
-}
-
-/* Draw a background world into shadow memory */
-static void vipDrawWorld(VB *sim, uint8_t *world, uint16_t bits) {
-    uint16_t   bgAttr;  /* BG map cell attributes */
-    int32_t    bx;      /* BG source X */
-    int32_t    by;      /* BG source Y */
-    uint8_t   *cell;    /* Pointer to BG map cell in host memory */
-    uint8_t   *chr;     /* Pointer to character data in host memory */
-    int32_t    cx;      /* BG cell/character source X */
-    int32_t    cy;      /* BG cell/character source Y */
-    uint8_t   *dest;    /* Pointer to output in shadow memory */
-    EyeAttribs ettr;    /* Eye attributes */
-    uint32_t   param;   /* Current line parameter address */
-    int8_t     pixel;   /* Character pixel value */
-    int32_t    i, x, y; /* Iterators */
-
-    /* World attributes */
-    WorldAttribs wttr;  /* Common attributes */
-    int32_t      dx;    /* Affine per-pixel X delta */
-    int32_t      dy;    /* Affine per-pixel Y delta */
-    int32_t      mp;    /* BG source parallax */
-    int32_t      mx;    /* BG source X */
-    int32_t      my;    /* BG source Y */
-    int16_t      hofst; /* H-bias shift */
-
-    /* Working variables */
-    ettr.bp = wttr.mp = wttr.mx = wttr.my = wttr.params = 0;
-
-    /* Parse attributes */
-    if (vipParseWorld(sim, world, bits, &wttr))
-        return; /* Window not in frame */
-
-    /* Draw the world */
-    for (i = 0; i < 2; i++) {
-
-        /* World is not visible */
-        if ((bits & (int32_t) 0x8000 >> i) == 0) /* LON, RON */
-            continue;
-
-        /* Process attributes */
-        if (vipParseEye(&wttr, &ettr, i))
-            continue;
-
-        /* Draw all rows */
-        for (y = wttr.top, param = wttr.params; y <= wttr.bottom; y++) {
-
-            /* Parse line parameters */
-            hofst = 0;
-            mp    = wttr.mp;
-            mx    = wttr.mx;
-            my    = wttr.my;
-            switch (wttr.bgm) {
-                case 1: /* H-bias */
-                    hofst  = SignExtend(vipParam(param | i << 1), 13);
-                    param += 4;
-                    break;
-                case 2: /* Affine */
-                    dx =  (int32_t) (int16_t) vipParam(param|6) << 7;
-                    dy =  (int32_t) (int16_t) vipParam(param|8) << 7;
-                    mp =  (int32_t) (int16_t) vipParam(param|2);
-                    mp = ettr.left - ettr.wx - ((mp < 0) ^ i ? mp : 0);
-                    mx = ((int32_t) (int16_t) vipParam(param  ) << 13) + dx*mp;
-                    my = ((int32_t) (int16_t) vipParam(param|4) << 13) + dy*mp;
-                    param += 16;
     }
 
-            /* Select output in shadow memory */
-            dest = &sim->vip.shadow[i][ettr.left * 224 + y];
-
-            /* Draw all columns */
-            for (x = ettr.left; x <= ettr.right; x++, dest += 224) {
-
-                /* Locate the pixel in the background */
-                if (wttr.bgm != 2) { /* Normal, H-bias */
-                    cx  = x - ettr.wx + mx + ettr.bp + hofst;
-                    cy  = y - wttr.gy + my;
-                } else { /* Affine */
-                    cx  = (int16_t) (mx >> 16);
-                    cy  = (int16_t) (my >> 16);
-                    mx += dx;
-                    my += dy;
-                }
-
-                /* Locate the BG map in the background */
-                bx   = SignExtend(cx >> 9, 23);
-                by   = SignExtend(cy >> 9, 23);
-                cell = NULL;
-
-                /* BG map is out of bounds */
-                if (
-                    bx < 0 || bx > wttr.bgw ||
-                    by < 0 || by > wttr.bgh
-                ) {
-                    if (wttr.over == NULL) {
-                        bx &= wttr.bgw;
-                        by &= wttr.bgh;
-                    } else cell = wttr.over;
-                }
-
-                /* Locate the cell in the BG map */
-                if (cell == NULL) {
-                    cell = &sim->vip.ram[
-                        0x20000 | ((
-                            wttr.base +
-                            wttr.bg[by << wttr.scx | bx]
-                        ) << 13) |
-                        (cy << 4 & 0x1F80) |
-                        (cx >> 2 & 0x007E)
-                    ];
-                }
-
-                /* Extract the pixel from the character */
-                bgAttr = busReadBuffer(cell, VB_U16);
-                chr    = vipCharacter(sim, bgAttr);
-                cx     = (bgAttr & 0x2000 ? 7 - cx : cx) & 7;
-                cy     = (bgAttr & 0x1000 ? 7 - cy : cy) & 7;
-                pixel  = chr[cy << 1 | cx >> 2] >> ((cx & 3) << 1) & 3;
-
-                /* Write the pixel into shadow memory */
-                if (pixel != 0)
-                    *dest = sim->vip.gplt[bgAttr >> 14 & 3][pixel];
-
-            } /* x */
-
-        } /* y */
-
-    } /* i */
-
 }
 
 /* Draw the current graphics configuration into shadow memory */
 static void vipRender(VB *sim) {
-    uint16_t  attr;   /* World attribute bits */
     int       group;  /* Next object group index */
     uint16_t *timing; /* Column timing in host memory */
-    uint8_t  *world;  /* World attribute source in host memory */
+    World    *world;  /* World attribute source in host memory */
     int32_t   x, y;   /* Iterators */
 
     /* Erase all pixels */
@@ -943,25 +1139,25 @@ static void vipRender(VB *sim) {
 
     /* Process all worlds */
     group = 3;
-    world = &sim->vip.ram[0x3DBE0]; /* World 31 */
-    for (x = 31; x >= 0; x--, world -= 32) {
-        attr = busReadBuffer(world, VB_U16);
+    for (x = 31; x >= 0; x--) {
+        world = &sim->vip.worlds[x];
 
         /* Non-graphical world */
-        if (attr & 0x0040) /* END */
+        if (world->end)
             break;    /* Control world */
-        if ((attr & 0xC000) == 0) /* LON, RON */
+        if (world->lron == 0)
             continue; /* Dummy world */
 
-        /* Object world */
-        if ((attr >> 12 & 3) == 3) {
+        /* Processing by world type */
+        switch (world->bgm) {
+            case 0: vipDrawNormal(sim, world); break;
+            case 1: vipDrawHBias (sim, world); break;
+            case 2: vipDrawAffine(sim, world); break;
+            case 3:
                 vipDrawObjects(sim, group);
                 group = (group - 1) & 3;
         }
 
-        /* Background world */
-        else if (attr & 0xC000) /* LON, RON */
-            vipDrawWorld(sim, world, attr);
     }
 
     /*
@@ -1134,6 +1330,10 @@ static void vipRead(VB *sim, uint32_t address, int type, int32_t *value) {
 
 /* Simulate a hardware reset */
 static void vipReset(VB *sim) {
+    Cell      *cell;  /* BG map cell state */
+    Character *chr;   /* Character state */
+    Object    *obj;   /* Object state */
+    World     *world; /* World state */
     int        x, y;  /* Iterators */
 
     /* Normal */
@@ -1159,6 +1359,53 @@ static void vipReset(VB *sim) {
             sim->vip.jplt[x][y] = 0;
         }
     }
+    for (x = 0; x < 0x10000; x++) {
+        cell = &sim->vip.cells[x];
+        cell->palette = sim->vip.gplt[0];
+        cell->pixels  = sim->vip.characters[0][0];
+    }
+    for (x = 0; x < 2048; x++) {
+        chr = &sim->vip.characters[x];
+        for (y = 0; y < 64; y++)
+            (*chr)[0][y] = (*chr)[1][y] = (*chr)[2][y] = (*chr)[3][y] = 0;
+    }
+    for (x = 0; x < 32; x++) {
+        world = &sim->vip.worlds[x];
+        world->bgm       = 0;
+        world->end       = 0;
+        world->gp        = 0;
+        world->gx        = 0;
+        world->gy        = 0;
+        world->mx        = 0;
+        world->mp        = 0;
+        world->my        = 0;
+        world->over      = 0;
+        world->overplane = &sim->vip.cells[0];
+        for (y = 0; y < 64; y++)
+            world->bg[0] = world->overplane;
+        world->bgHeight  = 512;
+        world->bgMaskX   = 0;
+        world->bgMaskY   = 0;
+        world->bgShift   = 0;
+        world->bgWidth   = 512;
+        world->hAffine   = 0;
+        world->hNaffine  = 0;
+        world->height    = 8;
+        world->lron      = 0;
+        world->paramBase = 0;
+        world->wAffine   = 0;
+        world->wNaffine  = 0;
+        world->width     = 0;
+    }
+    for (x = 0; x < 1024; x++) {
+        obj = &sim->vip.objects[x];
+        obj->cell.palette = sim->vip.jplt[0];
+        obj->cell.pixels  = sim->vip.characters[0][0];
+        obj->jp           = 0;
+        obj->jx           = 0;
+        obj->jy           = 0;
+        obj->lron         = 0;
+    }
 
     /* Display processor extra (the hardware does not do this) */
     sim->vip.dp.fclk    = 0;
@@ -1206,9 +1453,28 @@ static void vipWrite(VB*sim,uint32_t address,int type,int32_t value,int debug){
     address &= 0x0007FFFF;
 
     /* RAM */
-    if (address < 0x40000)
+    if (address < 0x40000) {
         busWriteBuffer(&sim->vip.ram[address], type, value);
 
+        /* Character memory */
+        if ((address & 0x26000) == 0x06000) {
+            address = (address & 0x18000) >> 2 | (address & 0x01FFF);
+            vipWriteChr(sim, address, type, value);
+        }
+
+        /* BG map memory */
+        if (address >= 0x20000)
+            vipWriteCell(sim, address & 0x1FFFF, type, value);
+
+        /* World memory */
+        if ((address & 0x3FC00) == 0x3D800)
+            vipWriteWorld(sim, address &0x003FF, type, value);
+
+        /* Object memory */
+        if (address >= 0x3E000)
+            vipWriteObject(sim, address & 0x01FFF, type, value);
+    }
+
     /* Unmapped */
     else if (address < 0x5E000)
         ;
@@ -1223,6 +1489,7 @@ static void vipWrite(VB*sim,uint32_t address,int type,int32_t value,int debug){
 
     /* Mirrors of character memory */
     else {
+        vipWriteChr(sim, address & 0x07FFF, type, value);
         address = 0x06000 | (address << 2 & 0x18000) | (address & 0x01FFF);
         busWriteBuffer(&sim->vip.ram[address], type, value);
     }

core/vsu.c

@@ -74,49 +74,8 @@ static void vsuNextFreqMod(VB *sim, Channel *chan) {
 }
 
 /* Process one channel */
-static void vsuEmulateChannel(VB *sim, int index, uint32_t clocks) {
+static void vsuEmulateChannel(VB *sim, Channel *chan) {
     uint32_t bit; /* Pseudorandom bit */
-    Channel *chan;    /* Channel handle */
-    int      freqmod; /* Frequency modifications enabled */
-    uint32_t until;   /* Clocks to process sub-channel components */
-
-    /* Select channel */
-    chan = &sim->vsu.channels[index];
-
-    /* Channel is disabled */
-    if (!chan->int_.enb)
-        return;
-
-    /* Frequency modifications are active */
-    freqmod =
-        index == 4           &&        /* Channel 5 */
-        sim->vsu.freqmod.enb &&        /* Modifications enabled */
-        sim->vsu.freqmod.interval != 0 /* Modifications valid */
-    ;
-
-    /* Process all clocks */
-    do {
-
-        /* Clocks until next state change */
-        until = clocks;
-        if (chan->clocks < until)
-            until = chan->clocks;
-        if (chan->env.enb && chan->env.clocks < until)
-            until = chan->env.clocks;
-        if (chan->int_.auto_ && chan->int_.clocks < until)
-            until = chan->int_.clocks;
-        if (freqmod && sim->vsu.freqmod.clocks < until)
-            until = sim->vsu.freqmod.clocks;
-
-        /* Manage clocks */
-        clocks       -= until;
-        chan->clocks -= until;
-        if (chan->env.enb)
-            chan->env.clocks -= until;
-        if (chan->int_.auto_)
-            chan->int_.clocks -= until;
-        if (freqmod)
-            sim->vsu.freqmod.clocks -= until;
 
     /* Automatic shutoff */
     if (chan->int_.auto_ && chan->int_.clocks == 0) {
@@ -124,11 +83,11 @@ static void vsuEmulateChannel(VB *sim, int index, uint32_t clocks) {
         return;
     }
 
-        /* Next sample */
+    /* Next input sample */
     if (chan->clocks == 0) {
 
         /* Wave */
-            if (index != 5) {
+        if (chan != &sim->vsu.channels[5]) {
             chan->clocks =  4 * (2048 - (uint32_t) chan->freq.current);
             chan->wave.sample = (chan->wave.sample + 1) & 31;
         }
@@ -158,7 +117,7 @@ static void vsuEmulateChannel(VB *sim, int index, uint32_t clocks) {
     }
 
     /* Frequency modification */
-        if (freqmod && sim->vsu.freqmod.clocks == 0) {
+    if (chan->freqmod && sim->vsu.freqmod.clocks == 0) {
         chan->freq.current = sim->vsu.freqmod.next;
         vsuNextFreqMod(sim, chan);
         if (!chan->int_.enb)
@@ -167,8 +126,6 @@ static void vsuEmulateChannel(VB *sim, int index, uint32_t clocks) {
             (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
     }
 
-    } while (clocks != 0);
-
 }
 
 /* Produce output for a channel */
@@ -230,6 +187,8 @@ static void vsuWriteEV1(VB *sim, int index, uint8_t value) {
             sim->vsu.freqmod.func = value >> 4 & 1;
             sim->vsu.freqmod.rep  = value >> 5 & 1;
             vsuNextFreqMod(sim, chan);
+            chan->freqmod =
+                sim->vsu.freqmod.enb && sim->vsu.freqmod.interval != 0;
             break;
 
         case 5: /* Channel 6 */
@@ -313,6 +272,8 @@ static void vsuWriteSWP(VB *sim, uint8_t value) {
         (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
     if (clocks < sim->vsu.freqmod.clocks)
         sim->vsu.freqmod.clocks = clocks;
+    sim->vsu.channels[4].freqmod =
+        sim->vsu.freqmod.enb && sim->vsu.freqmod.interval != 0;
 }
 
 
@@ -321,6 +282,8 @@ static void vsuWriteSWP(VB *sim, uint8_t value) {
 
 /* Process component */
 static void vsuEmulate(VB *sim, uint32_t clocks) {
+    Channel *chan;      /* Input channel */
+    uint32_t chantil;   /* Clocks until next channel state update */
     float    i0;        /* Current analog input sample */
     float    o0;        /* Current analog output sample */
     uint16_t output[2]; /* Digital output samples */
@@ -340,12 +303,54 @@ static void vsuEmulate(VB *sim, uint32_t clocks) {
         sim->vsu.clocks -= until;
 
         /* Process all channels */
-        for (x = 0; x < 6; x++)
-            vsuEmulateChannel(sim, x, until);
+        for (x = 0; x < 6; x++) {
+            chan    = &sim->vsu.channels[x];
+            chantil = until;
+
+            /* Process all clocks */
+            while (chan->int_.enb && chantil != 0) {
+
+                /* Determine when the next state change will occur */
+                if (chan->until == 0) {
+
+                    /* Clocks until next state change */
+                    chan->until = chan->clocks;
+                    if (chan->env.enb && chan->env.clocks < chan->until)
+                        chan->until = chan->env.clocks;
+                    if (chan->int_.auto_ && chan->int_.clocks < chan->until)
+                        chan->until = chan->int_.clocks;
+                    if (chan->freqmod && sim->vsu.freqmod.clocks < chan->until)
+                        chan->until = sim->vsu.freqmod.clocks;
+
+                    /* Manage clocks */
+                    chan->clocks -= chan->until;
+                    if (chan->env.enb)
+                        chan->env.clocks -= chan->until;
+                    if (chan->int_.auto_)
+                        chan->int_.clocks -= chan->until;
+                    if (chan->freqmod)
+                        sim->vsu.freqmod.clocks -= chan->until;
+                }
+
+                /* Manage clocks */
+                if (chan->until > chantil) {
+                    chan->until -= chantil;
+                    chantil      = 0;
+                } else {
+                    chantil     -= chan->until;
+                    chan->until  = 0;
+                }
+
+                /* Update channel state */
+                if (chan->until == 0)
+                    vsuEmulateChannel(sim, chan);
+            }
+
+        }
 
         /* Wait for the current sample to finish */
         if (sim->vsu.clocks != 0)
-            continue;
+            return;
 
         /* Compute the output sample */
         output[0] = output[1] = 0;
@@ -416,6 +421,8 @@ static void vsuReset(VB *sim) {
     for (x = 0; x < 6; x++) {
         chan = &sim->vsu.channels[x];
         chan->clocks        = 0;
+        chan->freqmod       = 0;
+        chan->until         = 0;
         chan->env.clocks    = 0;
         chan->env.enb       = 0;
         chan->env.dir       = 0;

util/disassembler.c

@@ -1,4 +1,4 @@
-/* This file is included into vb.c and cannot be compiled on its own. */
+/* This file is included into vbu.c and cannot be compiled on its own. */
 #ifdef VBUAPI
 
 
@@ -449,12 +449,6 @@ static VBU_DasmLine* dasmGrow(
     return *lines == NULL ? NULL : &(*lines)[index];
 }
 
-/* Determine the size of an instruction */
-static uint32_t dasmInstSize(VB *sim, uint32_t address) {
-    unsigned opcode = vbRead(sim, address, VB_U16) >> 10 & 63;
-    return opcode < 0x20 || opcode == 0x32 || opcode == 0x36 ? 2 : 4;
-}
-
 /* Format an operand */
 static void dasmOperand(char *dest, VBU_DasmConfig *config,
     VBU_DasmLine *line, uint8_t type) {
@@ -515,10 +509,12 @@ static int dasmLine(VB *sim, uint32_t *address, uint32_t pc,
     /* Process non-text members */
     line = &(*lines)[index];
     line->address    = *address;
-    line->codeLength = dasmInstSize(sim, *address);
+    line->codeLength = vbuCodeSize(sim, *address);
     line->isPC       = *address == pc;
     for (x = 0; x < line->codeLength; x++)
         line->code[x] = vbRead(sim, *address + x, VB_U8);
+
+    /* Advance to the next instruction or PC, whichever is sooner */
     *address += pc != *address && pc - *address < line->codeLength ?
         pc - *address : line->codeLength;
 
@@ -660,9 +656,11 @@ static VBU_DasmLine* dasmDisassemble(VB *sim, uint32_t address,
         }
 
         /* Check if the instruction contains the reference address */
-        size = dasmInstSize(sim, addr);
+        size = vbuCodeSize(sim, addr);
         if (address - addr < size)
             break;
+
+        /* Advance to the next instruction or PC, whichever is sooner */
         addr += addr != pc && pc - addr < size ? pc - addr : size;
     }
 
@@ -674,7 +672,7 @@ static VBU_DasmLine* dasmDisassemble(VB *sim, uint32_t address,
 
     /* Keep decoding until the first line of output */
     else for (; line < 0; line++)
-        addr += dasmInstSize(sim, addr);
+        addr += vbuCodeSize(sim, addr);
 
     /* Working variables */
     size   = length * sizeof (VBU_DasmLine);

util/vbu.c

@@ -38,6 +38,12 @@ static int32_t SignExtend(int32_t value, int32_t bits) {
 
 /******************************* API Commands ********************************/
 
+/* Determine the size in bytes of an instruction */
+VBUAPI int vbuCodeSize(VB *sim, uint32_t address) {
+    int opcode = vbRead(sim, address, VB_U16) >> 10 & 63;
+    return opcode < 0x20 || opcode == 0x32 || opcode == 0x36 ? 2 : 4;
+}
+
 /* Initialize disassembler options with default settings */
 VBUAPI VBU_DasmConfig* vbuDasmInit(VBU_DasmConfig *config) {
     config->bcondNotation     = VBU_JOINED;

util/vbu.h

@@ -85,6 +85,7 @@ typedef struct {
 
 /******************************* API Commands ********************************/
 
+VBUAPI int             vbuCodeSize   (VB *sim, uint32_t address);
 VBUAPI VBU_DasmConfig* vbuDasmInit   (VBU_DasmConfig *config);
 VBUAPI VBU_DasmLine*   vbuDisassemble(VB *sim, uint32_t address, VBU_DasmConfig *config, unsigned length, int line);