diff --git a/core/vip.c b/core/vip.c
index eeb2628..c026cf3 100644
--- a/core/vip.c
+++ b/core/vip.c
@@ -42,14 +42,14 @@ static const uint8_t BG_TEMPLATES[][64] = {
 
 /* 8-bit color magnitude by brightness level */
 static const uint8_t BRIGHT8[] = {
-      0, 10, 16, 21, 25, 30, 33, 37, 40, 44, 47, 50, 53, 56, 59, 61,
-     64, 67, 69, 72, 74, 77, 79, 82, 84, 86, 89, 91, 93, 95, 97,100,
-    102,104,106,108,110,112,114,116,118,120,122,124,126,128,130,131,
-    133,135,137,139,141,142,144,146,148,149,151,153,155,156,158,160,
-    161,163,165,166,168,170,171,173,175,176,178,179,181,183,184,186,
-    187,189,190,192,194,195,197,198,200,201,203,204,206,207,209,210,
-    212,213,215,216,217,219,220,222,223,225,226,227,229,230,232,233,
-    235,236,237,239,240,241,243,244,246,247,248,250,251,252,254,255
+      0,  2,  4,  6,  8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30,
+     32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62,
+     64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94,
+     96, 98,100,102,104,106,108,110,112,114,116,118,120,122,124,126,
+    129,131,133,135,137,139,141,143,145,147,149,151,153,155,157,159,
+    161,163,165,167,169,171,173,175,177,179,181,183,185,187,189,191,
+    193,195,197,199,201,203,205,207,209,211,213,215,217,219,221,223,
+    225,227,229,231,233,235,237,239,241,243,245,247,249,251,253,255
 };
 
 
@@ -68,10 +68,9 @@ static int32_t vipReadPalette(uint8_t *entries) {
 
 /* Raise an interrupt request */
 static void vipThrow(VB *sim, uint16_t cause) {
-    if (!(sim->vip.intenb & cause))
-        return;
     sim->vip.intpnd |= cause;
-    sim->cpu.irq    |= 0x0010;
+    if (sim->vip.intenb & cause)
+        sim->cpu.irq |= 0x0010;
 }
 
 /* Write a palette */
@@ -422,10 +421,9 @@ static void vipTransferColumn(VB *sim, int32_t eye) {
 
     /* Output is disabled */
     if ((sim->vip.dp.disp & sim->vip.dp.synce) == 0) {
-        for (z = 0; z < 0x15000; z += 4) {
-            busWriteBuffer(dest, VB_S32, 0);
-            dest += 4;
-        }
+        for (y = 0; y < 224; y += 16)
+        for (z = 0; z < 16; z++, dest += 384)
+            *dest = 0;
         return;
     }
 
@@ -838,7 +836,10 @@ static void vipDrawWorld(VB *sim, uint8_t *world, uint16_t attr) {
                         bx &= bgw;
                         by &= bgh;
                     }
-                    else cell = over;
+                    else {
+                        cell = over;
+                        continue; /* TODO: Research overplane */
+                    }
                 }
 
                 /* Locate the cell in the BG map */
diff --git a/core/vsu.c b/core/vsu.c
index 891cb0a..46faa10 100644
--- a/core/vsu.c
+++ b/core/vsu.c
@@ -164,7 +164,7 @@ static void vsuEmulateChannel(VB *sim, int index, uint32_t clocks) {
             if (!chan->int_.enb)
                 return;
             sim->vsu.freqmod.clocks = (uint32_t) sim->vsu.freqmod.interval *
-                (sim->vsu.freqmod.clk == 0 ? 19201 : 153610);
+                (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
         }
 
     } while (clocks != 0);
@@ -207,6 +207,8 @@ static void vsuWriteEV0(VB *sim, int index, uint8_t value) {
     chan->env.interval = value      &  7;
     chan->env.value    = value >> 4 & 15;
     chan->env.reload   = chan->env.value;
+    if (index == 4)
+        vsuNextFreqMod(sim, chan);
 
     /* Configure state */
     chan->env.clocks = 307220 * ((uint32_t) chan->env.interval + 1);
@@ -243,6 +245,8 @@ static void vsuWriteFQH(VB *sim, int index, uint16_t value) {
     value = value << 8 & 0x0700;
     chan->freq.current = (chan->freq.current & 0x00FF) | value;
     chan->freq.written = (chan->freq.written & 0x00FF) | value;
+    if (index == 4)
+        vsuNextFreqMod(sim, chan);
 }
 
 /* Write a value to S*FQL */
@@ -250,6 +254,8 @@ static void vsuWriteFQL(VB *sim, int index, uint8_t value) {
     Channel *chan = &sim->vsu.channels[index];
     chan->freq.current = (chan->freq.current & 0x0700) | value;
     chan->freq.written = (chan->freq.written & 0x0700) | value;
+    if (index == 4)
+        vsuNextFreqMod(sim, chan);
 }
 
 /* Write a value to S*INT */
@@ -274,7 +280,7 @@ static void vsuWriteINT(VB *sim, int index, uint8_t value) {
     }
     if (index == 4) {
         sim->vsu.freqmod.clocks = (uint32_t) sim->vsu.freqmod.interval *
-            (sim->vsu.freqmod.clk ? 153610 : 19201);
+            (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
         sim->vsu.freqmod.sample = 0;
     }
 
@@ -297,14 +303,14 @@ static void vsuWriteSWP(VB *sim, uint8_t value) {
     uint32_t clocks;
 
     /* Parse fields */
-    sim->vsu.freqmod.clk      = value >> 7 &  1;
-    sim->vsu.freqmod.dir      = value >> 3 &  1;
-    sim->vsu.freqmod.interval = value >> 4 & 15;
-    sim->vsu.freqmod.shift    = value      &  7;
+    sim->vsu.freqmod.clk      = value >> 7 & 1;
+    sim->vsu.freqmod.dir      = value >> 3 & 1;
+    sim->vsu.freqmod.interval = value >> 4 & 7;
+    sim->vsu.freqmod.shift    = value      & 7;
 
     /* Configure state */
     clocks = (uint32_t) sim->vsu.freqmod.interval *
-        (sim->vsu.freqmod.clk ? 153610 : 19201);
+        (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
     if (clocks < sim->vsu.freqmod.clocks)
         sim->vsu.freqmod.clocks = clocks;
 }