Genoa Unknown 486: Port 92h controls the exact same gate as the KBC, fixes #4660.

src/include/86box/port_92.h

@@ -37,6 +37,7 @@ extern void port_92_add(void *priv);
 extern void port_92_remove(void *priv);
 
 extern const device_t port_92_device;
+extern const device_t port_92_key_device;
 extern const device_t port_92_inv_device;
 extern const device_t port_92_word_device;
 extern const device_t port_92_pci_device;

src/machine/m_at_386dx_486.c

@@ -2333,7 +2333,7 @@ machine_at_genoa486_init(const machine_t *model)
     machine_at_common_init(model);
 
     device_add(&compaq_genoa_device);
-    device_add(&port_92_device);
+    device_add(&port_92_key_device);
 
     device_add(&keyboard_at_ami_device);
 

src/port_92.c

@@ -36,6 +36,7 @@
 #define PORT_92_PCI   4
 #define PORT_92_RESET 8
 #define PORT_92_A20   16
+#define PORT_92_KEY   32
 
 static uint8_t
 port_92_readb(uint16_t port, void *priv)
@@ -46,7 +47,10 @@ port_92_readb(uint16_t port, void *priv)
     if (port == 0x92) {
         /* Return bit 1 directly from mem_a20_alt, so the
            pin can be reset independently of the device. */
-        ret = (dev->reg & ~0x03) | (mem_a20_alt & 2) | (cpu_alt_reset & 1);
+        if (dev->flags & PORT_92_KEY)
+            ret = (dev->reg & ~0x03) | (mem_a20_key & 2) | (cpu_alt_reset & 1);
+        else
+            ret = (dev->reg & ~0x03) | (mem_a20_alt & 2) | (cpu_alt_reset & 1);
 
         if (dev->flags & PORT_92_INV)
             ret |= 0xfc;
@@ -94,8 +98,11 @@ port_92_writeb(uint16_t port, uint8_t val, void *priv)
 
     dev->reg = val & 0x03;
 
-    if ((mem_a20_alt ^ val) & 2) {
-        mem_a20_alt = (val & 2);
+    if (dev->flags & PORT_92_KEY) {
+        mem_a20_key = val & 2;
+        mem_a20_recalc();
+    } else if ((mem_a20_alt ^ val) & 2) {
+        mem_a20_alt = (mem_a20_alt & 0xfd) | (val & 2);
         mem_a20_recalc();
     }
 
@@ -234,6 +241,20 @@ const device_t port_92_device = {
     .config        = NULL
 };
 
+const device_t port_92_key_device = {
+    .name          = "Port 92 Register (using A20 key)",
+    .internal_name = "port_92_key",
+    .flags         = 0,
+    .local         = PORT_92_KEY,
+    .init          = port_92_init,
+    .close         = port_92_close,
+    .reset         = NULL,
+    { .available = NULL },
+    .speed_changed = NULL,
+    .force_redraw  = NULL,
+    .config        = NULL
+};
+
 const device_t port_92_inv_device = {
     .name          = "Port 92 Register (inverted bits 2-7)",
     .internal_name = "port_92_inv",