diff --git a/devices/common/pci/pcidevice.cpp b/devices/common/pci/pcidevice.cpp
index 615487c..016f891 100644
--- a/devices/common/pci/pcidevice.cpp
+++ b/devices/common/pci/pcidevice.cpp
@@ -100,11 +100,7 @@ void PCIDevice::pci_cfg_write(uint32_t reg_offs, uint32_t value, AccessDetails &
     case PCI_CFG_BAR3:
     case PCI_CFG_BAR4:
     case PCI_CFG_BAR5:
-        if (value == 0xFFFFFFFFUL) {
-            this->do_bar_sizing((reg_offs - 0x10) >> 2);
-        } else {
-            this->set_bar_value((reg_offs - 0x10) >> 2, value);
-        }
+        this->set_bar_value((reg_offs - 0x10) >> 2, value);
         break;
     case PCI_CFG_ROM_BAR:
         if ((value & this->exp_bar_cfg) == this->exp_bar_cfg) {
@@ -207,23 +203,75 @@ int PCIDevice::attach_exp_rom_image(const std::string img_path)
 
 void PCIDevice::do_bar_sizing(int bar_num)
 {
-    this->bars[bar_num] = this->bars_cfg[bar_num];
 }
 
 void PCIDevice::set_bar_value(int bar_num, uint32_t value)
 {
     uint32_t bar_cfg = this->bars_cfg[bar_num];
-    if (bar_cfg & 1) {
-        this->bars[bar_num] = (value & 0xFFFFFFFCUL) | (bar_cfg & 3);
-    } else {
-        if (bar_cfg & 6) {
-            ABORT_F("Invalid or unsupported PCI space type: %d", (bar_cfg >> 1) & 3);
-        }
-        this->bars[bar_num] = (value & 0xFFFFFFF0UL) | (bar_cfg & 0xF);
+    switch (bars_typ[bar_num]) {
+        case BAR_Unused:
+            return;
+
+        case BAR_IO_16Bit:
+        case BAR_IO_32Bit:
+            this->bars[bar_num] = (value & bar_cfg & ~3) | (bar_cfg & 3);
+            break;
+
+        case BAR_MEM_20Bit:
+        case BAR_MEM_32Bit:
+        case BAR_MEM_64Bit:
+            this->bars[bar_num] = (value & bar_cfg & ~0xF) | (bar_cfg & 0xF);
+            break;
+
+        case BAR_MEM_64BitHi:
+            this->bars[bar_num] = (value & bar_cfg);
+            break;
     }
+
+    if (value == 0xFFFFFFFFUL) {
+        do_bar_sizing(bar_num);
+        return;
+    }
+
     this->pci_notify_bar_change(bar_num);
 }
 
+void PCIDevice::finish_config_bars()
+{
+    for (int bar_num = 0; bar_num < 6; bar_num++) {
+        uint32_t bar_cfg = this->bars_cfg[bar_num];
+        if (bar_cfg & 1) {
+            bars_typ[bar_num] = (bar_cfg & 0xffff0000) ? BAR_IO_32Bit : BAR_IO_16Bit;
+        }
+        else if (bar_cfg != 0) {
+            int pci_space_type = (bar_cfg >> 1) & 3;
+            switch (pci_space_type) {
+                case 0:
+                    bars_typ[bar_num] = BAR_MEM_32Bit;
+                    break;
+                case 1:
+                    bars_typ[bar_num] = BAR_MEM_20Bit;
+                    break;
+                case 2:
+                    if (bar_num > 4) {
+                        ABORT_F("%s: BAR %d cannot be 64-bit", this->pci_name.c_str(), bar_num);
+                    }
+                    else if (this->bars_cfg[bar_num+1] == 0) {
+                        ABORT_F("%s: 64-bit BAR %d has zero for upper 32 bits", this->pci_name.c_str(), bar_num);
+                    }
+                    else {
+                        bars_typ[bar_num++] = BAR_MEM_64Bit;
+                        bars_typ[bar_num] = BAR_MEM_64BitHi;
+                    }
+                    break;
+                case 3:
+                    ABORT_F("%s: invalid or unsupported PCI space type %d for BAR %d", this->pci_name.c_str(), pci_space_type, bar_num);
+                    break;
+            } // switch pci_space_type
+        } // if BAR_MEM
+    } // for bar_num
+}
+
 void PCIDevice::map_exp_rom_mem()
 {
     uint32_t rom_addr, rom_size;
diff --git a/devices/common/pci/pcidevice.h b/devices/common/pci/pcidevice.h
index 147a59c..c215ea2 100644
--- a/devices/common/pci/pcidevice.h
+++ b/devices/common/pci/pcidevice.h
@@ -58,6 +58,16 @@ enum {
     PCI_VENDOR_NVIDIA   = 0x10DE,
 };
 
+/** PCI BAR types */
+enum PCIBarType {
+    BAR_Unused,
+    BAR_IO_16Bit,
+    BAR_IO_32Bit,
+    BAR_MEM_20Bit, // < 1M
+    BAR_MEM_32Bit,
+    BAR_MEM_64Bit,
+    BAR_MEM_64BitHi,
+};
 
 class PCIDevice : public MMIODevice {
 public:
@@ -108,6 +118,7 @@ public:
 protected:
     void do_bar_sizing(int bar_num);
     void set_bar_value(int bar_num, uint32_t value);
+    void finish_config_bars();
     void map_exp_rom_mem();
 
     std::string pci_name;      // human-readable device name
@@ -132,6 +143,7 @@ protected:
 
     uint32_t    bars[6] = { 0 };     // base address registers
     uint32_t    bars_cfg[6] = { 0 }; // configuration values for base address registers
+    PCIBarType  bars_typ[6] = { BAR_Unused }; // types for base address registers
 
     uint32_t    exp_bar_cfg  = 0;    // expansion ROM configuration
     uint32_t    exp_rom_bar  = 0;    // expansion ROM base address register
diff --git a/devices/ioctrl/grandcentral.cpp b/devices/ioctrl/grandcentral.cpp
index 56309d8..18fc5f2 100644
--- a/devices/ioctrl/grandcentral.cpp
+++ b/devices/ioctrl/grandcentral.cpp
@@ -43,6 +43,7 @@ GrandCentral::GrandCentral() : PCIDevice("mac-io/grandcentral"), InterruptCtrl()
     this->class_rev   = 0xFF000002;
     this->cache_ln_sz = 8;
     this->bars_cfg[0] = 0xFFFE0000UL; // declare 128Kb of memory-mapped I/O space
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);
diff --git a/devices/ioctrl/heathrow.cpp b/devices/ioctrl/heathrow.cpp
index 782af0d..9331fb0 100644
--- a/devices/ioctrl/heathrow.cpp
+++ b/devices/ioctrl/heathrow.cpp
@@ -55,6 +55,7 @@ HeathrowIC::HeathrowIC() : PCIDevice("mac-io/heathrow"), InterruptCtrl()
     this->cache_ln_sz = 8;
     this->lat_timer   = 0x40;
     this->bars_cfg[0] = 0xFFF80000UL; // declare 512Kb of memory-mapped I/O space
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);
diff --git a/devices/ioctrl/ohare.cpp b/devices/ioctrl/ohare.cpp
index 4cf8df6..50b1d03 100644
--- a/devices/ioctrl/ohare.cpp
+++ b/devices/ioctrl/ohare.cpp
@@ -37,6 +37,7 @@ OHare::OHare() : PCIDevice("mac-io/ohare"), InterruptCtrl()
     this->class_rev   = 0xFF000001;
     this->cache_ln_sz = 8;
     this->bars_cfg[0] = 0xFFF80000UL; // declare 512Kb of memory-mapped I/O space
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);
diff --git a/devices/video/atimach64gx.cpp b/devices/video/atimach64gx.cpp
index b903fcc..fa975f2 100644
--- a/devices/video/atimach64gx.cpp
+++ b/devices/video/atimach64gx.cpp
@@ -45,6 +45,7 @@ AtiMach64Gx::AtiMach64Gx()
     this->device_id   = ATI_MACH64_GX_DEV_ID;
     this->class_rev   = (0x030000 << 8) | 3;
     this->bars_cfg[0] = 0xFF000000UL; // declare main aperture (16MB)
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);
diff --git a/devices/video/atirage.cpp b/devices/video/atirage.cpp
index c88bd64..f24c2c9 100644
--- a/devices/video/atirage.cpp
+++ b/devices/video/atirage.cpp
@@ -127,6 +127,7 @@ ATIRage::ATIRage(uint16_t dev_id)
     this->bars_cfg[0] = 0xFF000000UL; // declare main aperture (16MB)
     this->bars_cfg[1] = 0xFFFFFF01UL; // declare I/O region (256 bytes)
     this->bars_cfg[2] = 0xFFFFF000UL; // declare register aperture (4KB)
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);
diff --git a/devices/video/control.cpp b/devices/video/control.cpp
index cfbcedc..30d26cd 100644
--- a/devices/video/control.cpp
+++ b/devices/video/control.cpp
@@ -62,6 +62,7 @@ ControlVideo::ControlVideo()
     this->bars_cfg[0] = 0xFFFFFFFFUL; // I/O region (4 bytes but it's weird because bit 1 is set)
     this->bars_cfg[1] = 0xFFFFF000UL; // base address for the HW registers (4KB)
     this->bars_cfg[2] = 0xFC000000UL; // base address for the VRAM (64MB)
+    this->finish_config_bars();
 
     this->pci_notify_bar_change = [this](int bar_num) {
         this->notify_bar_change(bar_num);