diff --git a/src/include/86box/vid_8514a.h b/src/include/86box/vid_8514a.h
index 9d19d916c..5aa8927e0 100644
--- a/src/include/86box/vid_8514a.h
+++ b/src/include/86box/vid_8514a.h
@@ -37,6 +37,13 @@ typedef enum {
     EXTENSIONS_MAX
 } ibm8514_extensions_t;
 
+typedef enum {
+    VGA_MODE = 0,
+    IBM_MODE,
+    ATI_MODE,
+    MODE_MAX
+} ibm8514_mode_t;
+
 typedef struct hwcursor8514_t {
     int      ena;
     int      x;
@@ -202,6 +209,7 @@ typedef struct ibm8514_t {
     int      split;
     int      h_disp;
     int      h_total;
+    int      h_sync_start;
     int      h_sync_width;
     int      h_disp_time;
     int      rowoffset;
@@ -260,6 +268,7 @@ typedef struct ibm8514_t {
     int      ext_pitch;
     int      ext_crt_pitch;
     ibm8514_extensions_t extensions;
+    ibm8514_mode_t mode;
     int      onboard;
     int      linear;
     uint32_t vram_amount;
diff --git a/src/video/vid_8514a.c b/src/video/vid_8514a.c
index 97202340d..b1e38fef7 100644
--- a/src/video/vid_8514a.c
+++ b/src/video/vid_8514a.c
@@ -911,8 +911,10 @@ ibm8514_accel_in(uint16_t port, svga_t *svga)
 
     switch (port) {
         case 0x2e8:
-            if (dev->vc == dev->v_syncstart)
-                temp |= 0x02;
+            if (dev->vc == dev->v_syncstart) {
+                if (dev->accel.advfunc_cntl & 0x04)
+                    temp |= 0x02;
+            }
 
             ibm8514_log("Read: Display Status1=%02x.\n", temp);
             break;
@@ -3817,7 +3819,7 @@ ibm8514_recalctimings(svga_t *svga)
     } else {
         if (dev->on) {
             dev->hdisp = (dev->hdisped + 1) << 3;
-            dev->h_total = dev->htotal + 1;
+            dev->h_total = (dev->htotal + 1) << 3;
 
             if (dev->h_total == 1) /*Default to 1024x768 87hz 8514/A htotal timings if it goes to 0.*/
                 dev->h_total = 0x9e;
@@ -3827,10 +3829,14 @@ ibm8514_recalctimings(svga_t *svga)
                 dev->vdisp += 2;
 
             dev->v_total = dev->v_total_reg + 1;
+            if (dev->v_total == 1)
+                dev->v_total = 0x0669;
             if (dev->interlace)
                 dev->v_total >>= 1;
 
             dev->v_syncstart = dev->v_sync_start + 1;
+            if (dev->v_syncstart == 1)
+                dev->v_syncstart = 0x0601;
             if (dev->interlace)
                 dev->v_syncstart >>= 1;
 
diff --git a/src/video/vid_ati_mach8.c b/src/video/vid_ati_mach8.c
index 46d3d98c1..d4ec7a4aa 100644
--- a/src/video/vid_ati_mach8.c
+++ b/src/video/vid_ati_mach8.c
@@ -2699,93 +2699,80 @@ ati_render_32bpp(svga_t *svga)
 }
 
 /*The situation is the following:
-  When ATI mode is selected, allow complete auto-detection.
-  But when 8514/A mode is selected, allow detection based on the shadow register sets.
+  When ATI (0x4aee) mode is selected, allow complete auto-detection.
+  When 8514/A (0x4ae8) mode is selected, allow detection based on the shadow register sets.
 */
 static void
 mach_set_resolution(mach_t *mach, svga_t *svga)
 {
-    ibm8514_t    *dev  = (ibm8514_t *) svga->dev8514;
-    int           ret  = 0;
+    ibm8514_t    *dev = (ibm8514_t *) svga->dev8514;
 
-    dev->h_total = dev->htotal + 1;
-
-    if (dev->h_total == 1) /*Default to 1024x768 87hz 8514/A htotal timings if it goes to 0.*/
-        dev->h_total = 0x9e;
+    dev->h_total = (dev->htotal + 1) << 3;
+    if (dev->h_total == 8) /*Default to 1024x768 87hz 8514/A htotal timings if it goes to 0.*/
+        dev->h_total = 0x9e << 3;
 
     dev->hdisp = (dev->hdisped + 1) << 3;
 
     dev->vdisp = (dev->v_disp + 1) >> 1;
-    if ((dev->vdisp == 478) || (dev->vdisp == 598) || (dev->vdisp == 766) || (dev->vdisp == 1022))
+    if ((dev->vdisp == 478) || (dev->vdisp == 598) || (dev->vdisp == 766) || (dev->vdisp == 898) || (dev->vdisp == 1022))
         dev->vdisp += 2;
 
     dev->v_total = dev->v_total_reg + 1;
+    if (dev->v_total == 1)
+        dev->v_total = 0x0669;
 
     dev->v_syncstart = dev->v_sync_start + 1;
+    if (dev->v_syncstart == 1)
+        dev->v_syncstart = 0x0601;
 
-    mach_log("VSYNCSTART=%d, VTOTAL=%d, interlace=%02x, vdisp=%d.\n", dev->v_syncstart, dev->v_total, dev->interlace, dev->vdisp);
+    mach_log("ATI Mode: set=%02x, dispcntl=%02x, h_total=%d, hdisp=%d, vdisp=%d, v_total=%04x, v_syncstart=%04x, hsync_start=%d, hsync_width=%d, clocksel=%02x, advancedcntl=%02x.\n", mach->shadow_set & 0x03, dev->disp_cntl, dev->h_total, dev->hdisp, dev->vdisp, dev->v_total, dev->v_syncstart, dev->hsync_start, dev->hsync_width, mach->accel.clock_sel & 0xff, dev->accel.advfunc_cntl & 0x05);
+    if ((dev->disp_cntl >> 5) == 1) { /*Enable the 8514/A subsystem and set modes according to the shadow sets if needed.*/
+        switch (mach->shadow_set & 0x03) {
+            case 0x01:
+                if (!(dev->accel.advfunc_cntl & 0x04)) {
+                    dev->h_total = 0x64 << 3;
+                    dev->hdisp = 640;
+                    dev->vdisp = 480;
+                    dev->v_total = 0x0419;
+                    dev->v_syncstart = 0x03d7;
+                }
+                break;
+            case 0x02:
+                if (dev->accel.advfunc_cntl & 0x04) {
+                    dev->h_total = 0x9e << 3;
+                    dev->hdisp = 1024;
+                    dev->vdisp = 768;
+                    dev->v_total = 0x0669;
+                    dev->v_syncstart = 0x0601;
+                }
+                break;
 
-    if (!ATI_MACH32) {
-        if ((mach->accel.clock_sel & 0x01) &&
-            !(dev->accel.advfunc_cntl & 0x01))
-            ret = 2;
-        else if ((dev->accel.advfunc_cntl & 0x01) &&
-                 !(mach->accel.clock_sel & 0x01))
-            ret = 1;
-        else if ((!(dev->accel.advfunc_cntl & 0x01) && (mach->old_on1 & 0x01)) ||
-                (!(mach->accel.clock_sel & 0x01) && (mach->old_on2 & 0x01)))
-            ret = 0;
-    } else {
-        if ((mach->accel.clock_sel & 0x01) && !(mach->old_on2 & 0x01) &&
-            !(dev->accel.advfunc_cntl & 0x01))
-            ret = 2;
-        else if ((dev->accel.advfunc_cntl & 0x01) && !(mach->old_on1 & 0x01) &&
-                 !(mach->accel.clock_sel & 0x01))
-            ret = 1;
-        else if ((!(dev->accel.advfunc_cntl & 0x01) && (mach->old_on1 & 0x01)) ||
-                (!(mach->accel.clock_sel & 0x01) && (mach->old_on2 & 0x01)))
-            ret = 0;
-    }
-
-    if (ret) {
-        if (ret == 2)
-            svga_recalctimings(svga);
-        else {
-            switch (mach->shadow_set & 0x03) {
-                case 0x00:
-                    if (mach->crt_resolution)
-                        svga_recalctimings(svga);
-                    else {
-                        if (dev->accel.advfunc_cntl & 0x04) {
-                            if (dev->hdisp == 640) {
-                                dev->hdisp = 1024;
-                                dev->vdisp = 768;
-                                mach_log("1024x768.\n");
-                            }
-                        } else {
-                            if (dev->hdisp == 1024) {
-                                dev->hdisp = 640;
-                                dev->vdisp = 480;
-                                mach_log("640x480.\n");
-                            }
-                        }
-                        svga_recalctimings(svga);
-                    }
-                    break;
-                case 0x01:
-                    mach->crt_resolution = 0x01;
-                    break;
-                case 0x02:
-                    mach->crt_resolution = 0x02;
-                    break;
-                default:
-                    break;
+            default:
+                break;
+        }
+        svga_recalctimings(svga);
+    } else if ((dev->disp_cntl >> 5) == 2) { /*Reset 8514/A to defaults if needed.*/
+        if (dev->accel.advfunc_cntl & 0x04) {
+            if (dev->hdisp == 640) {
+                dev->h_total = 0x9e << 3;
+                dev->hdisp = 1024;
+                dev->vdisp = 768;
+                dev->v_total = 0x0669;
+                dev->v_syncstart = 0x0601;
+                svga_recalctimings(svga);
+            }
+        } else {
+            if (dev->hdisp == 1024) {
+                dev->h_total = 0x64 << 3;
+                dev->hdisp = 640;
+                dev->vdisp = 480;
+                dev->v_total = 0x0419;
+                dev->v_syncstart = 0x03d7;
+                svga_recalctimings(svga);
             }
         }
-    } else
+    } else /*No change (type 0) or reset type 3.*/
         svga_recalctimings(svga);
-
-    mach_log("Shadow set ATI=%x, shadow set 8514/A and on1=%x, on2=%x, resolution h=%d, v=%d, vtotal=%d, vsyncstart=%d, crtres=%d, ret=%d, actual passthrough=%x.\n", mach->shadow_set & 0x03, dev->accel.advfunc_cntl & 0x05, mach->accel.clock_sel & 0x01, dev->hdisp, dev->vdisp, dev->v_total, dev->v_syncstart, mach->crt_resolution, ret, dev->on);
 }
 
 void
@@ -2845,7 +2832,7 @@ ati8514_recalctimings(svga_t *svga)
         svga->render8514 = ibm8514_render_8bpp;
 
     } else
-        mach->crt_resolution = 0;
+        dev->mode = VGA_MODE;
 }
 
 static void
@@ -2899,9 +2886,9 @@ mach_recalctimings(svga_t *svga)
             svga->ati_4color = 0;
     }
 
-    mach_log("ON=%d, override=%d, gelo=%04x, gehi=%04x, vgahdisp=%d.\n", dev->on, svga->override, mach->accel.ge_offset_lo, mach->accel.ge_offset_hi, svga->hdisp);
+    mach_log("ON=%d, override=%d, gelo=%04x, gehi=%04x, crtlo=%04x, crthi=%04x, vgahdisp=%d.\n", dev->on, svga->override, mach->accel.ge_offset_lo, mach->accel.ge_offset_hi, mach->accel.crt_offset_lo, mach->accel.crt_offset_hi, svga->hdisp);
     if (dev->on) {
-        dev->memaddr_latch                   = 0; /*(mach->accel.crt_offset_lo | (mach->accel.crt_offset_hi << 16)) << 2;*/
+        dev->memaddr_latch              = 0; /*(mach->accel.crt_offset_lo | (mach->accel.crt_offset_hi << 16)) << 2;*/
         dev->interlace                  = !!(dev->disp_cntl & 0x10);
         dev->pitch                      = dev->ext_pitch;
         dev->rowoffset                  = dev->ext_crt_pitch;
@@ -2949,8 +2936,8 @@ mach_recalctimings(svga_t *svga)
         if (ATI_MACH32) {
             switch ((mach->shadow_set >> 8) & 0x03) {
                 case 0x00:
-                    mach->accel.src_pitch = ((mach->accel.ge_pitch & 0xff) << 3);
-                    mach->accel.dst_pitch = ((mach->accel.ge_pitch & 0xff) << 3);
+                    mach->accel.src_pitch = dev->pitch;
+                    mach->accel.dst_pitch = dev->pitch;
                     mach->accel.src_ge_offset = (mach->accel.ge_offset_lo | (mach->accel.ge_offset_hi << 16));
                     mach->accel.dst_ge_offset = (mach->accel.ge_offset_lo | (mach->accel.ge_offset_hi << 16));
                     if (dev->bpp) {
@@ -2972,7 +2959,7 @@ mach_recalctimings(svga_t *svga)
                     dev->accel.dst_ge_offset = mach->accel.dst_ge_offset;
                     break;
                 case 0x01:
-                    mach->accel.dst_pitch = ((mach->accel.ge_pitch & 0xff) << 3);
+                    mach->accel.dst_pitch = dev->pitch;
                     mach->accel.dst_ge_offset = (mach->accel.ge_offset_lo | (mach->accel.ge_offset_hi << 16));
                     if (dev->bpp)
                         mach->accel.dst_ge_offset <<= 1;
@@ -2987,7 +2974,7 @@ mach_recalctimings(svga_t *svga)
                     dev->accel.dst_ge_offset = mach->accel.dst_ge_offset;
                     break;
                 case 0x02:
-                    mach->accel.src_pitch = ((mach->accel.ge_pitch & 0xff) << 3);
+                    mach->accel.src_pitch = dev->pitch;
                     mach->accel.src_ge_offset = (mach->accel.ge_offset_lo | (mach->accel.ge_offset_hi << 16));
                     if (dev->bpp)
                         mach->accel.src_ge_offset <<= 1;
@@ -3067,7 +3054,7 @@ mach_recalctimings(svga_t *svga)
             svga->render8514 = ibm8514_render_8bpp;
         }
     } else {
-        mach->crt_resolution = 0;
+        dev->mode = VGA_MODE;
         if (!svga->scrblank && (svga->crtc[0x17] & 0x80) && svga->attr_palette_enable) {
             mach_log("GDCREG5=%02x, ATTR10=%02x, ATI B0 bit 5=%02x, ON=%d.\n",
                      svga->gdcreg[5] & 0x60, svga->attrregs[0x10] & 0x40, mach->regs[0xb0] & 0x20, dev->on);
@@ -3240,7 +3227,7 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
                 mach_log("ATI 8514/A: V_DISP write 16E8=%d, vdisp2=%d.\n", dev->v_disp, dev->v_disp2);
                 mach_log("ATI 8514/A: (0x%04x): vdisp=0x%02x.\n", port, val);
             } else {
-                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) {  /*For 8514/A mode, take the shadow sets into account.*/
+                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) { /*For 8514/A mode, take the shadow sets into account.*/
                     if (!(mach->shadow_cntl & 0x20)) {
                         WRITE8(port, dev->v_disp, val);
                         dev->v_disp &= 0x1fff;
@@ -3265,7 +3252,7 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
 
         case 0x1ae8:
             if (len == 2) {
-                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) {  /*For 8514/A mode, take the shadow sets into account.*/
+                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) { /*For 8514/A mode, take the shadow sets into account.*/
                     if (!(mach->shadow_cntl & 0x10) && val) {
                         dev->v_sync_start = val;
                         dev->v_sync_start &= 0x1fff;
@@ -3274,7 +3261,7 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
                 mach_log("ATI 8514/A: V_SYNCSTART write 1AE8 = %d\n", dev->v_syncstart);
                 mach_log("ATI 8514/A: (0x%04x): vsyncstart=0x%02x.\n", port, val);
             } else {
-                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) {  /*For 8514/A mode, take the shadow sets into account.*/
+                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) { /*For 8514/A mode, take the shadow sets into account.*/
                     if (!(mach->shadow_cntl & 0x10)) {
                         WRITE8(port, dev->v_sync_start, val);
                         dev->v_sync_start &= 0x1fff;
@@ -3285,7 +3272,7 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
             break;
         case 0x1ae9:
             if (len == 1) {
-                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) {  /*For 8514/A mode, take the shadow sets into account.*/
+                if ((mach->accel.clock_sel & 0x01) || (!(mach->accel.clock_sel & 0x01) && (mach->shadow_set & 0x03))) { /*For 8514/A mode, take the shadow sets into account.*/
                     if (!(mach->shadow_cntl & 0x10)) {
                         WRITE8(port, dev->v_sync_start, val >> 8);
                         dev->v_sync_start &= 0x1fff;
@@ -3334,7 +3321,6 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
 
         case 0x4ae8:
         case 0x4ae9:
-            mach->old_on1 = dev->accel.advfunc_cntl & 0x01;
             WRITE8(port, dev->accel.advfunc_cntl, val);
             if (len == 2) {
                 WRITE8(port + 1, dev->accel.advfunc_cntl, val >> 8);
@@ -3348,6 +3334,7 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
                 }
             }
 
+            dev->mode = IBM_MODE;
             mach_log("[%04X:%08X]: ATI 8514/A: (0x%04x): ON=%d, valxor=%x, shadow crt=%x, hdisp=%d, vdisp=%d, extmode=%02x, accelbpp=%d, crt=%d, crtres=%d.\n",
                      CS, cpu_state.pc, port, val & 0x01, dev->on, dev->accel.advfunc_cntl & 0x04, dev->hdisp, dev->vdisp, mach->regs[0xb0] & 0x20, dev->accel_bpp, dev->_8514crt, mach->crt_resolution);
 
@@ -3686,7 +3673,11 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
             } else
                 dev->_8514crt = 1;
 
-            mach_set_resolution(mach, svga);
+            if (dev->mode != VGA_MODE)
+                mach_set_resolution(mach, svga);
+            else
+                svga_recalctimings(svga);
+
             if (ATI_GRAPHICS_ULTRA || ATI_MACH32)
                 mach32_updatemapping(mach, svga);
 
@@ -3779,13 +3770,15 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
 
         case 0x4aee:
         case 0x4aef:
-            mach->old_on2 = mach->accel.clock_sel & 0x01;
             WRITE8(port, mach->accel.clock_sel, val);
             if (len == 2) {
                 WRITE8(port + 1, mach->accel.clock_sel, val >> 8);
             }
-            dev->on = mach->accel.clock_sel & 0x01;
+            if (!(dev->accel.advfunc_cntl & 0x01))
+                dev->on = mach->accel.clock_sel & 0x01;
+
             dev->vendor_mode = 1;
+            dev->mode = ATI_MODE;
 
             mach_log("[%04X:%08X]: ATI 8514/A: (0x%04x): ON=%d, val=%04x, xor=%d, hdisp=%d, vdisp=%d, accelbpp=%d.\n",
                      CS, cpu_state.pc, port, mach->accel.clock_sel & 0x01, val, dev->on, dev->hdisp, dev->vdisp, dev->accel_bpp);
@@ -3937,7 +3930,11 @@ mach_accel_out_fifo(mach_t *mach, svga_t *svga, ibm8514_t *dev, uint16_t port, u
                 }
                 svga_set_ramdac_type(svga, !!(mach->accel.ext_ge_config & 0x4000));
                 mach_log("ATI 8514/A: (0x%04x) Extended Configuration=%04x, val=%04x.\n", port, mach->accel.ext_ge_config, val);
-                mach_set_resolution(mach, svga);
+                if (dev->mode != VGA_MODE)
+                    mach_set_resolution(mach, svga);
+                else
+                    svga_recalctimings(svga);
+
                 mach32_updatemapping(mach, svga);
             } else
                 ati_eeprom_write(&mach->eeprom, !!(mach->accel.ext_ge_config & 0x04), !!(mach->accel.ext_ge_config & 0x02), !!(mach->accel.ext_ge_config & 0x01));
@@ -7195,6 +7192,7 @@ mach8_init(const device_t *info)
     mach_io_set(mach);
     mach->accel.cmd_type = -2;
     dev->accel.cmd_back = 1;
+    dev->mode = IBM_MODE;
 
     if (ATI_MACH32) {
         svga->decode_mask     = (4 << 20) - 1;
@@ -7256,6 +7254,7 @@ ati8514_init(svga_t *svga, void *ext8514, void *dev8514)
     dev->disp_cntl = 0x33;
     mach->accel.clock_sel = 0x1c;
     dev->accel.cmd_back = 1;
+    dev->mode = IBM_MODE;
 
     io_sethandler(0x02ea, 4, ati8514_in, NULL, NULL, ati8514_out, NULL, NULL, svga);
     ati8514_io_set(svga);
diff --git a/src/video/vid_svga.c b/src/video/vid_svga.c
index c9e02ac78..2073fb8c0 100644
--- a/src/video/vid_svga.c
+++ b/src/video/vid_svga.c
@@ -977,29 +977,57 @@ svga_recalctimings(svga_t *svga)
         }
     }
 
-#ifdef TBD
+#if TBD
     if (ibm8514_active && (svga->dev8514 != NULL)) {
         if (dev->on) {
-            uint32_t dot8514 = dev->h_blankstart;
-            uint32_t adj_dot8514 = dev->h_blankstart;
-            uint32_t eff_mask8514 = 0x0000001f;
-            dev->hblank_sub = 0;
+            uint32_t _8514_dot = dev->h_sync_start;
+            uint32_t _8514_adj_dot = dev->h_sync_start;
+            uint32_t _8514_eff_mask = (dev->h_blank_end_val & ~0x0000001f) ? dev->h_blank_end_mask : 0x0000001f;
+            dev->h_blank_sub = 0;
 
-            while (adj_dot8514 < (dev->h_total << 1)) {
-                if (dot8514 == dev->h_total)
-                    dot8514 = 0;
+            mach_log("8514/A: HDISP=%d, HDISPED=%d, Blank: %04i-%04i, Total: %04i, "
+                     "Mask: %02X, ADJ_DOT=%04i.\n", dev->hdisp, (dev->hdisped + 1) << 3,
+                     dev->h_sync_start, dev->h_blank_end_val,
+                     dev->h_total, _8514_eff_mask, _8514_adj_dot);
 
-                if (adj_dot8514 >= dev->h_total)
-                    dev->hblank_sub++;
+            while (_8514_adj_dot < (dev->h_total << 1)) {
+                if (_8514_dot == dev->h_total)
+                    _8514_dot = 0;
 
-                if ((dot8514 & eff_mask8514) == (dev->h_blank_end_val & eff_mask8514))
+                if (_8514_adj_dot >= dev->h_total)
+                    dev->h_blank_sub++;
+
+                mach_log("8514/A: Loop: adjdot=%d, htotal=%d, dotmask=%02x, "
+                         "hblankendvalmask=%02x, blankendval=%02x.\n", adj_dot,
+                         dev->h_total, _8514_dot & _8514_eff_mask, dev->h_blank_end_val & _8514_eff_mask,
+                         dev->h_blank_end_val);
+                if ((_8514_dot & _8514_eff_mask) == (dev->h_blank_end_val & _8514_eff_mask))
                     break;
 
-                dot8514++;
-                adj_dot8514++;
+                _8514_dot++;
+                _8514_adj_dot++;
             }
 
-            dev->h_disp -= dev->hblank_sub;
+            uint32_t _8514_hd = dev->hdisp;
+            dev->hdisp -= dev->h_blank_sub;
+
+            svga->left_overscan = svga->x_add = (dev->h_total - _8514_adj_dot - 1) << 3;
+            svga->monitor->mon_overscan_x = svga->x_add + (dev->h_sync_start << 3) - _8514_hd + 8;
+            svga->monitor->mon_overscan_x++;
+
+            if ((dev->hdisp >= 2048) || (svga->left_overscan < 0)) {
+                svga->left_overscan = svga->x_add = 0;
+                svga->monitor->mon_overscan_x = 0;
+            }
+
+            /* - 1 because + 1 but also - 2 to compensate for the + 2 added to vtotal above. */
+            svga->y_add = svga->vtotal - svga->vblankend - 1;
+            svga->monitor->mon_overscan_y = svga->y_add + abs(svga->vblankstart - svga->dispend);
+
+            if ((svga->dispend >= 2048) || (svga->y_add < 0)) {
+                svga->y_add = 0;
+                svga->monitor->mon_overscan_y = 0;
+            }
         }
     }
 #endif
@@ -1194,18 +1222,24 @@ svga_recalctimings(svga_t *svga)
         video_force_resize_set_monitor(1, svga->monitor_index);
 
     svga->force_shifter_bypass = 0;
-    if (svga->hdisp == 320 && svga->dispend >= 400 && !svga->override && svga->render != svga_render_8bpp_clone_highres) {
-        svga->hdisp *= 2;
-        if (svga->render == svga_render_16bpp_highres) svga->render = svga_render_16bpp_lowres;
-        else if (svga->render == svga_render_15bpp_highres) svga->render = svga_render_15bpp_lowres;
-        else if (svga->render == svga_render_15bpp_mix_highres) svga->render = svga_render_15bpp_mix_lowres;
-        else if (svga->render == svga_render_24bpp_highres) svga->render = svga_render_24bpp_lowres;
-        else if (svga->render == svga_render_32bpp_highres) svga->render = svga_render_32bpp_lowres;
+    if ((svga->hdisp == 320) && (svga->dispend >= 400) && !svga->override && (svga->render != svga_render_8bpp_clone_highres)) {
+        svga->hdisp <<= 1;
+        if (svga->render == svga_render_16bpp_highres)
+            svga->render = svga_render_16bpp_lowres;
+        else if (svga->render == svga_render_15bpp_highres)
+            svga->render = svga_render_15bpp_lowres;
+        else if (svga->render == svga_render_15bpp_mix_highres)
+            svga->render = svga_render_15bpp_mix_lowres;
+        else if (svga->render == svga_render_24bpp_highres)
+            svga->render = svga_render_24bpp_lowres;
+        else if (svga->render == svga_render_32bpp_highres)
+            svga->render = svga_render_32bpp_lowres;
         else if (svga->render == svga_render_8bpp_highres) {
             svga->render = svga_render_8bpp_lowres;
             svga->force_shifter_bypass = 1;
         }
-        else svga->hdisp /= 2;
+        else
+            svga->hdisp >>= 1;
     }
 }