diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
index 55dfe5036f40..66ca5c0df6ef 100644
--- a/hw/m68k/q800.c
+++ b/hw/m68k/q800.c
@@ -533,10 +533,11 @@ static void q800_init(MachineState *machine)
 
     sysbus = SYS_BUS_DEVICE(dev);
     sysbus_realize_and_unref(sysbus, &error_fatal);
-    sysbus_connect_irq(sysbus, 0, qdev_get_gpio_in(via2_dev,
-                                                   VIA2_IRQ_SCSI_BIT));
-    sysbus_connect_irq(sysbus, 1, qdev_get_gpio_in(via2_dev,
-                                                   VIA2_IRQ_SCSI_DATA_BIT));
+    /* SCSI and SCSI data IRQs are negative edge triggered */
+    sysbus_connect_irq(sysbus, 0, qemu_irq_invert(qdev_get_gpio_in(via2_dev,
+                                                  VIA2_IRQ_SCSI_BIT)));
+    sysbus_connect_irq(sysbus, 1, qemu_irq_invert(qdev_get_gpio_in(via2_dev,
+                                                  VIA2_IRQ_SCSI_DATA_BIT)));
     sysbus_mmio_map(sysbus, 0, ESP_BASE);
     sysbus_mmio_map(sysbus, 1, ESP_PDMA);
 
diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index d8b35e6ca611..525e38ce9322 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -327,7 +327,9 @@ static void via1_sixty_hz(void *opaque)
     MOS6522State *s = MOS6522(v1s);
     qemu_irq irq = qdev_get_gpio_in(DEVICE(s), VIA1_IRQ_60HZ_BIT);
 
-    qemu_set_irq(irq, 1);
+    /* Negative edge trigger */
+    qemu_irq_lower(irq);
+    qemu_irq_raise(irq);
 
     via1_sixty_hz_update(v1s);
 }
@@ -338,7 +340,9 @@ static void via1_one_second(void *opaque)
     MOS6522State *s = MOS6522(v1s);
     qemu_irq irq = qdev_get_gpio_in(DEVICE(s), VIA1_IRQ_ONE_SECOND_BIT);
 
-    qemu_set_irq(irq, 1);
+    /* Negative edge trigger */
+    qemu_irq_lower(irq);
+    qemu_irq_raise(irq);
 
     via1_one_second_update(v1s);
 }
@@ -917,9 +921,11 @@ static uint64_t mos6522_q800_via2_read(void *opaque, hwaddr addr, unsigned size)
          * On a Q800 an emulated VIA2 is integrated into the onboard logic. The
          * expectation of most OSs is that the DRQ bit is live, rather than
          * latched as it would be on a real VIA so do the same here.
+         *
+         * Note: DRQ is negative edge triggered
          */
         val &= ~VIA2_IRQ_SCSI_DATA;
-        val |= (ms->last_irq_levels & VIA2_IRQ_SCSI_DATA);
+        val |= (~ms->last_irq_levels & VIA2_IRQ_SCSI_DATA);
         break;
     }
 
@@ -1146,7 +1152,8 @@ static void via2_nubus_irq_request(void *opaque, int n, int level)
         s->a |= (1 << n);
     }
 
-    qemu_set_irq(irq, level);
+    /* Negative edge trigger */
+    qemu_set_irq(irq, !level);
 }
 
 static void mos6522_q800_via2_init(Object *obj)
diff --git a/hw/misc/mos6522.c b/hw/misc/mos6522.c
index c67123f86442..f9e646350e67 100644
--- a/hw/misc/mos6522.c
+++ b/hw/misc/mos6522.c
@@ -64,14 +64,62 @@ static void mos6522_update_irq(MOS6522State *s)
 static void mos6522_set_irq(void *opaque, int n, int level)
 {
     MOS6522State *s = MOS6522(opaque);
+    int last_level = !!(s->last_irq_levels & (1 << n));
+    uint8_t last_ifr = s->ifr;
+    bool positive_edge = true;
+    int ctrl;
+
+    /*
+     * SR_INT is managed by mos6522 instances and cleared upon SR
+     * read. It is only the external CA1/2 and CB1/2 lines that
+     * are edge-triggered and latched in IFR
+     */
+    if (n != SR_INT_BIT && level == last_level) {
+        return;
+    }
 
-    if (level) {
+    /* Detect negative edge trigger */
+    if (last_level == 1 && level == 0) {
+        positive_edge = false;
+    }
+
+    switch (n) {
+    case CA2_INT_BIT:
+        ctrl = (s->pcr & CA2_CTRL_MASK) >> CA2_CTRL_SHIFT;
+        if ((positive_edge && (ctrl & C2_POS)) ||
+             (!positive_edge && !(ctrl & C2_POS))) {
+            s->ifr |= 1 << n;
+        }
+        break;
+    case CA1_INT_BIT:
+        ctrl = (s->pcr & CA1_CTRL_MASK) >> CA1_CTRL_SHIFT;
+        if ((positive_edge && (ctrl & C1_POS)) ||
+             (!positive_edge && !(ctrl & C1_POS))) {
+            s->ifr |= 1 << n;
+        }
+        break;
+    case SR_INT_BIT:
         s->ifr |= 1 << n;
-    } else {
-        s->ifr &= ~(1 << n);
+        break;
+    case CB2_INT_BIT:
+        ctrl = (s->pcr & CB2_CTRL_MASK) >> CB2_CTRL_SHIFT;
+        if ((positive_edge && (ctrl & C2_POS)) ||
+             (!positive_edge && !(ctrl & C2_POS))) {
+            s->ifr |= 1 << n;
+        }
+        break;
+    case CB1_INT_BIT:
+        ctrl = (s->pcr & CB1_CTRL_MASK) >> CB1_CTRL_SHIFT;
+        if ((positive_edge && (ctrl & C1_POS)) ||
+             (!positive_edge && !(ctrl & C1_POS))) {
+            s->ifr |= 1 << n;
+        }
+        break;
     }
 
-    mos6522_update_irq(s);
+    if (s->ifr != last_ifr) {
+        mos6522_update_irq(s);
+    }
 
     if (level) {
         s->last_irq_levels |= 1 << n;
@@ -250,6 +298,7 @@ uint64_t mos6522_read(void *opaque, hwaddr addr, unsigned size)
 {
     MOS6522State *s = opaque;
     uint32_t val;
+    int ctrl;
     int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
     if (now >= s->timers[0].next_irq_time) {
@@ -263,12 +312,24 @@ uint64_t mos6522_read(void *opaque, hwaddr addr, unsigned size)
     switch (addr) {
     case VIA_REG_B:
         val = s->b;
+        ctrl = (s->pcr & CB2_CTRL_MASK) >> CB2_CTRL_SHIFT;
+        if (!(ctrl & C2_IND)) {
+            s->ifr &= ~CB2_INT;
+        }
+        s->ifr &= ~CB1_INT;
+        mos6522_update_irq(s);
         break;
     case VIA_REG_A:
        qemu_log_mask(LOG_UNIMP, "Read access to register A with handshake");
        /* fall through */
     case VIA_REG_ANH:
         val = s->a;
+        ctrl = (s->pcr & CA2_CTRL_MASK) >> CA2_CTRL_SHIFT;
+        if (!(ctrl & C2_IND)) {
+            s->ifr &= ~CA2_INT;
+        }
+        s->ifr &= ~CA1_INT;
+        mos6522_update_irq(s);
         break;
     case VIA_REG_DIRB:
         val = s->dirb;
@@ -335,6 +396,7 @@ void mos6522_write(void *opaque, hwaddr addr, uint64_t val, unsigned size)
 {
     MOS6522State *s = opaque;
     MOS6522DeviceClass *mdc = MOS6522_GET_CLASS(s);
+    int ctrl;
 
     trace_mos6522_write(addr, mos6522_reg_names[addr], val);
 
@@ -342,6 +404,12 @@ void mos6522_write(void *opaque, hwaddr addr, uint64_t val, unsigned size)
     case VIA_REG_B:
         s->b = (s->b & ~s->dirb) | (val & s->dirb);
         mdc->portB_write(s);
+        ctrl = (s->pcr & CB2_CTRL_MASK) >> CB2_CTRL_SHIFT;
+        if (!(ctrl & C2_IND)) {
+            s->ifr &= ~CB2_INT;
+        }
+        s->ifr &= ~CB1_INT;
+        mos6522_update_irq(s);
         break;
     case VIA_REG_A:
        qemu_log_mask(LOG_UNIMP, "Write access to register A with handshake");
@@ -349,6 +417,12 @@ void mos6522_write(void *opaque, hwaddr addr, uint64_t val, unsigned size)
     case VIA_REG_ANH:
         s->a = (s->a & ~s->dira) | (val & s->dira);
         mdc->portA_write(s);
+        ctrl = (s->pcr & CA2_CTRL_MASK) >> CA2_CTRL_SHIFT;
+        if (!(ctrl & C2_IND)) {
+            s->ifr &= ~CA2_INT;
+        }
+        s->ifr &= ~CA1_INT;
+        mos6522_update_irq(s);
         break;
     case VIA_REG_DIRB:
         s->dirb = val;
diff --git a/include/hw/misc/mos6522.h b/include/hw/misc/mos6522.h
index babea99e0626..0bc22a839576 100644
--- a/include/hw/misc/mos6522.h
+++ b/include/hw/misc/mos6522.h
@@ -65,6 +65,21 @@
 #define T1MODE             0xc0    /* Timer 1 mode */
 #define T1MODE_CONT        0x40    /*  continuous interrupts */
 
+/* Bits in PCR */
+#define CB2_CTRL_MASK      0xe0
+#define CB2_CTRL_SHIFT     5
+#define CB1_CTRL_MASK      0x10
+#define CB1_CTRL_SHIFT     4
+#define CA2_CTRL_MASK      0x0e
+#define CA2_CTRL_SHIFT     1
+#define CA1_CTRL_MASK      0x1
+#define CA1_CTRL_SHIFT     0
+
+#define C2_POS             0x2
+#define C2_IND             0x1
+
+#define C1_POS             0x1
+
 /* VIA registers */
 #define VIA_REG_B       0x00
 #define VIA_REG_A       0x01