diff --git a/src/include/86box/vid_svga.h b/src/include/86box/vid_svga.h
index b44f101cb..3e7c6f3fe 100644
--- a/src/include/86box/vid_svga.h
+++ b/src/include/86box/vid_svga.h
@@ -128,6 +128,8 @@ typedef struct svga_t {
     int hblank_sub;
     int hblank_end_val;
     int hblank_end_len;
+    int packed_4bpp;
+    int ati_4color;
 
     /*The three variables below allow us to implement memory maps like that seen on a 1MB Trio64 :
       0MB-1MB - VRAM
diff --git a/src/video/vid_ati18800.c b/src/video/vid_ati18800.c
index 09e813bab..b54f6b89e 100644
--- a/src/video/vid_ati18800.c
+++ b/src/video/vid_ati18800.c
@@ -186,8 +186,22 @@ ati18800_recalctimings(svga_t *svga)
         svga->gdcreg[5] &= ~0x40;
     }
 
-    if (ati18800->regs[0xb0] & 6)
+    if (ati18800->regs[0xb0] & 6) {
         svga->gdcreg[5] |= 0x40;
+        if ((ati18800->regs[0xb6] & 0x18) >= 0x10)
+            svga->packed_4bpp = 1;
+        else
+            svga->packed_4bpp = 0;
+    } else
+        svga->packed_4bpp = 0;
+
+    if ((ati18800->regs[0xb6] & 0x18) == 8) {
+        svga->hdisp <<= 1;
+        svga->htotal <<= 1;
+        svga->ati_4color = 1;
+    } else
+        svga->ati_4color = 0;
+
 
     if (!svga->scrblank && (svga->crtc[0x17] & 0x80) && svga->attr_palette_enable) {
          if ((svga->gdcreg[6] & 1) || (svga->attrregs[0x10] & 1)) {
@@ -215,8 +229,10 @@ ati18800_recalctimings(svga_t *svga)
                                 svga->render = svga_render_8bpp_lowres;
                             else {
                                 svga->render = svga_render_8bpp_highres;
-                                svga->ma_latch <<= 1;
-                                svga->rowoffset <<= 1;
+                                if (!svga->packed_4bpp) {
+                                    svga->ma_latch <<= 1;
+                                    svga->rowoffset <<= 1;
+                                }
                             }
                             break;
                     }
diff --git a/src/video/vid_ati28800.c b/src/video/vid_ati28800.c
index aa5800d1c..09d6279f4 100644
--- a/src/video/vid_ati28800.c
+++ b/src/video/vid_ati28800.c
@@ -400,7 +400,10 @@ ati28800k_in(uint16_t addr, void *priv)
 static void
 ati28800_recalctimings(svga_t *svga)
 {
-    const ati28800_t *ati28800 = (ati28800_t *) svga->priv;
+    ati28800_t       *ati28800 = (ati28800_t *) svga->priv;
+    int               clock_sel;
+
+    clock_sel = ((svga->miscout >> 2) & 3) | ((ati28800->regs[0xbe] & 0x10) >> 1) | ((ati28800->regs[0xb9] & 2) << 1);
 
     if (ati28800->regs[0xa3] & 0x10)
         svga->ma_latch |= 0x10000;
@@ -408,66 +411,13 @@ ati28800_recalctimings(svga_t *svga)
     if (ati28800->regs[0xb0] & 0x40)
         svga->ma_latch |= 0x20000;
 
-    switch (((ati28800->regs[0xbe] & 0x10) >> 1) | ((ati28800->regs[0xb9] & 2) << 1) | ((svga->miscout & 0x0C) >> 2)) {
-        case 0x00:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 42954000.0;
-            break;
-        case 0x01:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 48771000.0;
-            break;
-        case 0x02:
-            ati28800_log("clock 2\n");
-            break;
-        case 0x03:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 36000000.0;
-            break;
-        case 0x04:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 50350000.0;
-            break;
-        case 0x05:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 56640000.0;
-            break;
-        case 0x06:
-            ati28800_log("clock 2\n");
-            break;
-        case 0x07:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 44900000.0;
-            break;
-        case 0x08:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 30240000.0;
-            break;
-        case 0x09:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 32000000.0;
-            break;
-        case 0x0A:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 37500000.0;
-            break;
-        case 0x0B:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 39000000.0;
-            break;
-        case 0x0C:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 50350000.0;
-            break;
-        case 0x0D:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 56644000.0;
-            break;
-        case 0x0E:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 75000000.0;
-            break;
-        case 0x0F:
-            svga->clock = (cpuclock * (double) (1ULL << 32)) / 65000000.0;
-            break;
-        default:
-            break;
-    }
-
     if (ati28800->regs[0xb8] & 0x40)
         svga->clock *= 2;
 
     if (ati28800->regs[0xa7] & 0x80)
         svga->clock *= 3;
 
-    if (ati28800->regs[0xb6] & 0x10) {
+    if ((ati28800->regs[0xb6] & 0x18) >= 0x10) {
         svga->hdisp <<= 1;
         svga->htotal <<= 1;
         svga->rowoffset <<= 1;
@@ -476,10 +426,24 @@ ati28800_recalctimings(svga_t *svga)
 
     if (ati28800->regs[0xb0] & 0x20) {
         svga->gdcreg[5] |= 0x40;
-    }
+        if ((ati28800->regs[0xb6] & 0x18) >= 0x10)
+            svga->packed_4bpp = 1;
+        else
+            svga->packed_4bpp = 0;
+    } else
+        svga->packed_4bpp = 0;
 
-    if (!svga->scrblank && svga->attr_palette_enable) {
-        if ((svga->gdcreg[6] & 1) || (svga->attrregs[0x10] & 1)) {
+    if ((ati28800->regs[0xb6] & 0x18) == 8) {
+        svga->hdisp <<= 1;
+        svga->htotal <<= 1;
+        svga->ati_4color = 1;
+    } else
+        svga->ati_4color = 0;
+
+    if (!svga->scrblank && (svga->crtc[0x17] & 0x80) && svga->attr_palette_enable) {
+         if ((svga->gdcreg[6] & 1) || (svga->attrregs[0x10] & 1)) {
+            svga->clock = (cpuclock * (double) (1ULL << 32)) / svga->getclock(clock_sel, svga->clock_gen);
+            ati28800_log("SEQREG1 bit 3=%x. gdcreg5 bits 5-6=%02x, 4bit pel=%02x, planar 16color=%02x, apa mode=%02x, attregs10 bit 7=%02x.\n", svga->seqregs[1] & 8, svga->gdcreg[5] & 0x60, ati28800->regs[0xb3] & 0x40, ati28800->regs[0xac] & 0x40, ati28800->regs[0xb6] & 0x18, ati28800->svga.attrregs[0x10] & 0x80);
             switch (svga->gdcreg[5] & 0x60) {
                 case 0x00:
                     if (svga->seqregs[1] & 8) /*Low res (320)*/
@@ -502,8 +466,10 @@ ati28800_recalctimings(svga_t *svga)
                                 svga->render = svga_render_8bpp_lowres;
                             else {
                                 svga->render = svga_render_8bpp_highres;
-                                svga->rowoffset <<= 1;
-                                svga->ma_latch <<= 1;
+                                if (!svga->packed_4bpp) {
+                                    svga->ma_latch <<= 1;
+                                    svga->rowoffset <<= 1;
+                                }
                             }
                             break;
                         case 15:
@@ -516,7 +482,6 @@ ati28800_recalctimings(svga_t *svga)
                                 svga->ma_latch <<= 1;
                             }
                             break;
-
                         default:
                             break;
                     }
@@ -586,6 +551,8 @@ ati28800k_init(const device_t *info)
               ati28800k_in, ati28800k_out,
               NULL,
               NULL);
+    ati28800->svga.clock_gen = device_add(&ati18810_device);
+    ati28800->svga.getclock  = ics2494_getclock;
 
     io_sethandler(0x01ce, 0x0002, ati28800k_in, NULL, NULL, ati28800k_out, NULL, NULL, ati28800);
     io_sethandler(0x03c0, 0x0020, ati28800k_in, NULL, NULL, ati28800k_out, NULL, NULL, ati28800);
@@ -652,6 +619,8 @@ ati28800_init(const device_t *info)
               ati28800_in, ati28800_out,
               NULL,
               NULL);
+    ati28800->svga.clock_gen = device_add(&ati18810_device);
+    ati28800->svga.getclock  = ics2494_getclock;
 
     io_sethandler(0x01ce, 2,
                   ati28800_in, NULL, NULL,
diff --git a/src/video/vid_ati_mach8.c b/src/video/vid_ati_mach8.c
index 5b8dedfbe..e9118bfbc 100644
--- a/src/video/vid_ati_mach8.c
+++ b/src/video/vid_ati_mach8.c
@@ -2579,15 +2579,30 @@ mach_recalctimings(svga_t *svga)
     if (mach->regs[0xb0] & 0x40)
         svga->ma_latch |= 0x20000;
 
-    if (mach->regs[0xb6] & 0x10) {
+    if ((mach->regs[0xb6] & 0x18) >= 0x10) {
         svga->hdisp <<= 1;
         svga->htotal <<= 1;
         svga->rowoffset <<= 1;
         svga->gdcreg[5] &= ~0x40;
     }
 
-    if (mach->regs[0xb0] & 0x20)
+    if (mach->regs[0xb0] & 0x20) {
         svga->gdcreg[5] |= 0x40;
+        if ((mach->regs[0xb6] & 0x18) >= 0x10)
+            svga->packed_4bpp = 1;
+        else
+            svga->packed_4bpp = 0;
+    } else
+        svga->packed_4bpp = 0;
+
+    if ((dev->local & 0xff) < 0x02) {
+        if ((mach->regs[0xb6] & 0x18) == 8) {
+            svga->hdisp <<= 1;
+            svga->htotal <<= 1;
+            svga->ati_4color = 1;
+        } else
+            svga->ati_4color = 0;
+    }
 
     mach_log("ON[0]=%d, ON[1]=%d, exton[0]=%d, exton[1]=%d, vendormode0=%d, vendormode1=%d.\n", dev->on[0], dev->on[1], mach->ext_on[0], mach->ext_on[1], dev->vendor_mode[0], dev->vendor_mode[1]);
     if (dev->on[0] || dev->on[1]) {
@@ -2606,9 +2621,6 @@ mach_recalctimings(svga_t *svga)
             if (dev->dispend == 598)
                 dev->dispend += 2;
 
-            if (dev->h_disp == 1024)
-                dev->accel.advfunc_cntl |= 4; /*Bit 2 means high resolution e.g.: 1024x768*/
-
             if (dev->accel.advfunc_cntl & 4) {
                 if (mach->shadow_set & 2) {
                     if (dev->h_disp == 8) {
@@ -2784,8 +2796,10 @@ mach_recalctimings(svga_t *svga)
                                 svga->render = svga_render_8bpp_lowres;
                             else {
                                 svga->render = svga_render_8bpp_highres;
-                                svga->ma_latch <<= 1;
-                                svga->rowoffset <<= 1;
+                                if (!svga->packed_4bpp) {
+                                    svga->ma_latch <<= 1;
+                                    svga->rowoffset <<= 1;
+                                }
                             }
                             break;
                     }
@@ -3628,7 +3642,9 @@ mach_accel_out(uint16_t port, uint8_t val, mach_t *mach)
         case 0x6e8:
         case 0x6e9:
             if (!(port & 1)) {
-                if (!dev->on[0] || !dev->on[1])
+                if ((dev->vendor_mode[0] || dev->vendor_mode[1]) && ((mach->shadow_set & 3) == 0))
+                    dev->hdisp = val;
+                else if (!dev->on[0] || !dev->on[1])
                     dev->hdisp = val;
 
                 mach_log("ATI 8514/A: H_DISP write 06E8 = %d\n", dev->hdisp + 1);
@@ -3655,10 +3671,13 @@ mach_accel_out(uint16_t port, uint8_t val, mach_t *mach)
 
         case 0x16e8:
         case 0x16e9:
-            if (!dev->on[0] || !dev->on[1]) {
+            if ((dev->vendor_mode[0] || dev->vendor_mode[1]) && ((mach->shadow_set & 3) == 0)) {
+                WRITE8(port, dev->vdisp, val);
+            } else if (!dev->on[0] || !dev->on[1]) {
                 WRITE8(port, dev->vdisp, val);
-                dev->vdisp &= 0x1fff;
             }
+            dev->vdisp &= 0x1fff;
+            mach_log("ATI 8514/A: V_DISP write 16E8 = %d\n", (dev->vdisp >> 1) + 1);
             svga_recalctimings(svga);
             break;
 
@@ -3848,7 +3867,8 @@ mach_accel_out(uint16_t port, uint8_t val, mach_t *mach)
         case 0x5aef:
             WRITE8(port, mach->shadow_set, val);
             mach_log("ATI 8514/A: (0x%04x) val = %04x.\n", port, val);
-            svga_recalctimings(svga);
+            if (mach->shadow_set & 3)
+                svga_recalctimings(svga);
             break;
 
         case 0x5eee: