diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index f3f130ad96..e5658af922 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -27,7 +27,7 @@
 #include "sysemu/runstate.h"
 #include "qapi/error.h"
 #include "qemu/cutils.h"
-
+#include "trace.h"
 
 /*
  * VIAs: There are two in every machine,
@@ -278,6 +278,21 @@
 /* VIA returns time offset from Jan 1, 1904, not 1970 */
 #define RTC_OFFSET 2082844800
 
+enum {
+    REG_0,
+    REG_1,
+    REG_2,
+    REG_3,
+    REG_TEST,
+    REG_WPROTECT,
+    REG_PRAM_ADDR,
+    REG_PRAM_ADDR_LAST = REG_PRAM_ADDR + 19,
+    REG_PRAM_SECT,
+    REG_PRAM_SECT_LAST = REG_PRAM_SECT + 7,
+    REG_INVALID,
+    REG_EMPTY = 0xff,
+};
+
 static void via1_VBL_update(MOS6522Q800VIA1State *v1s)
 {
     MOS6522State *s = MOS6522(v1s);
@@ -360,10 +375,62 @@ static void via2_irq_request(void *opaque, int irq, int level)
     mdc->update_irq(s);
 }
 
+/*
+ * RTC Commands
+ *
+ * Command byte    Register addressed by the command
+ *
+ * z0000001        Seconds register 0 (lowest-order byte)
+ * z0000101        Seconds register 1
+ * z0001001        Seconds register 2
+ * z0001101        Seconds register 3 (highest-order byte)
+ * 00110001        Test register (write-only)
+ * 00110101        Write-Protect Register (write-only)
+ * z010aa01        RAM address 100aa ($10-$13) (first 20 bytes only)
+ * z1aaaa01        RAM address 0aaaa ($00-$0F) (first 20 bytes only)
+ * z0111aaa        Extended memory designator and sector number
+ *
+ * For a read request, z=1, for a write z=0
+ * The letter a indicates bits whose value depend on what parameter
+ * RAM byte you want to address
+ */
+static int via1_rtc_compact_cmd(uint8_t value)
+{
+    uint8_t read = value & 0x80;
+
+    value &= 0x7f;
+
+    /* the last 2 bits of a command byte must always be 0b01 ... */
+    if ((value & 0x78) == 0x38) {
+        /* except for the extended memory designator */
+        return read | (REG_PRAM_SECT + (value & 0x07));
+    }
+    if ((value & 0x03) == 0x01) {
+        value >>= 2;
+        if ((value & 0x1c) == 0) {
+            /* seconds registers */
+            return read | (REG_0 + (value & 0x03));
+        } else if ((value == 0x0c) && !read) {
+            return REG_TEST;
+        } else if ((value == 0x0d) && !read) {
+            return REG_WPROTECT;
+        } else if ((value & 0x1c) == 0x08) {
+            /* RAM address 0x10 to 0x13 */
+            return read | (REG_PRAM_ADDR + 0x10 + (value & 0x03));
+        } else if ((value & 0x43) == 0x41) {
+            /* RAM address 0x00 to 0x0f */
+            return read | (REG_PRAM_ADDR + (value & 0x0f));
+        }
+    }
+    return REG_INVALID;
+}
+
 static void via1_rtc_update(MacVIAState *m)
 {
     MOS6522Q800VIA1State *v1s = &m->mos6522_via1;
     MOS6522State *s = MOS6522(v1s);
+    int cmd, sector, addr;
+    uint32_t time;
 
     if (s->b & VIA1B_vRTCEnb) {
         return;
@@ -376,7 +443,9 @@ static void via1_rtc_update(MacVIAState *m)
             m->data_out |= s->b & VIA1B_vRTCData;
             m->data_out_cnt++;
         }
+        trace_via1_rtc_update_data_out(m->data_out_cnt, m->data_out);
     } else {
+        trace_via1_rtc_update_data_in(m->data_in_cnt, m->data_in);
         /* receive bits from the RTC */
         if ((v1s->last_b & VIA1B_vRTCClk) &&
             !(s->b & VIA1B_vRTCClk) &&
@@ -386,96 +455,132 @@ static void via1_rtc_update(MacVIAState *m)
             m->data_in <<= 1;
             m->data_in_cnt--;
         }
+        return;
     }
 
-    if (m->data_out_cnt == 8) {
-        m->data_out_cnt = 0;
-
-        if (m->cmd == 0) {
-            if (m->data_out & 0x80) {
-                /* this is a read command */
-                uint32_t time = m->tick_offset +
-                               (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) /
-                               NANOSECONDS_PER_SECOND);
-                if (m->data_out == 0x81) {        /* seconds register 0 */
-                    m->data_in = time & 0xff;
-                    m->data_in_cnt = 8;
-                } else if (m->data_out == 0x85) { /* seconds register 1 */
-                    m->data_in = (time >> 8) & 0xff;
-                    m->data_in_cnt = 8;
-                } else if (m->data_out == 0x89) { /* seconds register 2 */
-                    m->data_in = (time >> 16) & 0xff;
-                    m->data_in_cnt = 8;
-                } else if (m->data_out == 0x8d) { /* seconds register 3 */
-                    m->data_in = (time >> 24) & 0xff;
-                    m->data_in_cnt = 8;
-                } else if ((m->data_out & 0xf3) == 0xa1) {
-                    /* PRAM address 0x10 -> 0x13 */
-                    int addr = (m->data_out >> 2) & 0x03;
-                    m->data_in = v1s->PRAM[addr];
-                    m->data_in_cnt = 8;
-                } else if ((m->data_out & 0xf3) == 0xa1) {
-                    /* PRAM address 0x00 -> 0x0f */
-                    int addr = (m->data_out >> 2) & 0x0f;
-                    m->data_in = v1s->PRAM[addr];
-                    m->data_in_cnt = 8;
-                } else if ((m->data_out & 0xf8) == 0xb8) {
-                    /* extended memory designator and sector number */
-                    m->cmd = m->data_out;
-                }
-            } else {
-                /* this is a write command */
-                m->cmd = m->data_out;
+    if (m->data_out_cnt != 8) {
+        return;
+    }
+
+    m->data_out_cnt = 0;
+
+    trace_via1_rtc_internal_status(m->cmd, m->alt, m->data_out);
+    /* first byte: it's a command */
+    if (m->cmd == REG_EMPTY) {
+
+        cmd = via1_rtc_compact_cmd(m->data_out);
+        trace_via1_rtc_internal_cmd(cmd);
+
+        if (cmd == REG_INVALID) {
+            trace_via1_rtc_cmd_invalid(m->data_out);
+            return;
+        }
+
+        if (cmd & 0x80) { /* this is a read command */
+            switch (cmd & 0x7f) {
+            case REG_0...REG_3: /* seconds registers */
+                /*
+                 * register 0 is lowest-order byte
+                 * register 3 is highest-order byte
+                 */
+
+                time = m->tick_offset + (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL)
+                       / NANOSECONDS_PER_SECOND);
+                trace_via1_rtc_internal_time(time);
+                m->data_in = (time >> ((cmd & 0x03) << 3)) & 0xff;
+                m->data_in_cnt = 8;
+                trace_via1_rtc_cmd_seconds_read((cmd & 0x7f) - REG_0,
+                                                m->data_in);
+                break;
+            case REG_PRAM_ADDR...REG_PRAM_ADDR_LAST:
+                /* PRAM address 0x00 -> 0x13 */
+                m->data_in = v1s->PRAM[(cmd & 0x7f) - REG_PRAM_ADDR];
+                m->data_in_cnt = 8;
+                trace_via1_rtc_cmd_pram_read((cmd & 0x7f) - REG_PRAM_ADDR,
+                                             m->data_in);
+                break;
+            case REG_PRAM_SECT...REG_PRAM_SECT_LAST:
+                /*
+                 * extended memory designator and sector number
+                 * the only two-byte read command
+                 */
+                trace_via1_rtc_internal_set_cmd(cmd);
+                m->cmd = cmd;
+                break;
+            default:
+                g_assert_not_reached();
+                break;
             }
+            return;
+        }
+
+        /* this is a write command, needs a parameter */
+        if (cmd == REG_WPROTECT || !m->wprotect) {
+            trace_via1_rtc_internal_set_cmd(cmd);
+            m->cmd = cmd;
         } else {
+            trace_via1_rtc_internal_ignore_cmd(cmd);
+        }
+        return;
+    }
+
+    /* second byte: it's a parameter */
+    if (m->alt == REG_EMPTY) {
+        switch (m->cmd & 0x7f) {
+        case REG_0...REG_3: /* seconds register */
+            /* FIXME */
+            trace_via1_rtc_cmd_seconds_write(m->cmd - REG_0, m->data_out);
+            m->cmd = REG_EMPTY;
+            break;
+        case REG_TEST:
+            /* device control: nothing to do */
+            trace_via1_rtc_cmd_test_write(m->data_out);
+            m->cmd = REG_EMPTY;
+            break;
+        case REG_WPROTECT:
+            /* Write Protect register */
+            trace_via1_rtc_cmd_wprotect_write(m->data_out);
+            m->wprotect = !!(m->data_out & 0x80);
+            m->cmd = REG_EMPTY;
+            break;
+        case REG_PRAM_ADDR...REG_PRAM_ADDR_LAST:
+            /* PRAM address 0x00 -> 0x13 */
+            trace_via1_rtc_cmd_pram_write(m->cmd - REG_PRAM_ADDR, m->data_out);
+            v1s->PRAM[m->cmd - REG_PRAM_ADDR] = m->data_out;
+            m->cmd = REG_EMPTY;
+            break;
+        case REG_PRAM_SECT...REG_PRAM_SECT_LAST:
+            addr = (m->data_out >> 2) & 0x1f;
+            sector = (m->cmd & 0x7f) - REG_PRAM_SECT;
             if (m->cmd & 0x80) {
-                if ((m->cmd & 0xf8) == 0xb8) {
-                    /* extended memory designator and sector number */
-                    int sector = m->cmd & 0x07;
-                    int addr = (m->data_out >> 2) & 0x1f;
-
-                    m->data_in = v1s->PRAM[sector * 8 + addr];
-                    m->data_in_cnt = 8;
-                }
-            } else if (!m->wprotect) {
-                /* this is a write command */
-                if (m->alt != 0) {
-                    /* extended memory designator and sector number */
-                    int sector = m->cmd & 0x07;
-                    int addr = (m->alt >> 2) & 0x1f;
-
-                    v1s->PRAM[sector * 8 + addr] = m->data_out;
-
-                    m->alt = 0;
-                } else if (m->cmd == 0x01) { /* seconds register 0 */
-                    /* FIXME */
-                } else if (m->cmd == 0x05) { /* seconds register 1 */
-                    /* FIXME */
-                } else if (m->cmd == 0x09) { /* seconds register 2 */
-                    /* FIXME */
-                } else if (m->cmd == 0x0d) { /* seconds register 3 */
-                    /* FIXME */
-                } else if (m->cmd == 0x31) {
-                    /* Test Register */
-                } else if (m->cmd == 0x35) {
-                    /* Write Protect register */
-                    m->wprotect = m->data_out & 1;
-                } else if ((m->cmd & 0xf3) == 0xa1) {
-                    /* PRAM address 0x10 -> 0x13 */
-                    int addr = (m->cmd >> 2) & 0x03;
-                    v1s->PRAM[addr] = m->data_out;
-                } else if ((m->cmd & 0xf3) == 0xa1) {
-                    /* PRAM address 0x00 -> 0x0f */
-                    int addr = (m->cmd >> 2) & 0x0f;
-                    v1s->PRAM[addr] = m->data_out;
-                } else if ((m->cmd & 0xf8) == 0xb8) {
-                    /* extended memory designator and sector number */
-                    m->alt = m->cmd;
-                }
+                /* it's a read */
+                m->data_in = v1s->PRAM[sector * 32 + addr];
+                m->data_in_cnt = 8;
+                trace_via1_rtc_cmd_pram_sect_read(sector, addr,
+                                                  sector * 32 + addr,
+                                                  m->data_in);
+                m->cmd = REG_EMPTY;
+            } else {
+                /* it's a write, we need one more parameter */
+                trace_via1_rtc_internal_set_alt(addr, sector, addr);
+                m->alt = addr;
             }
+            break;
+        default:
+            g_assert_not_reached();
+            break;
         }
-        m->data_out = 0;
+        return;
     }
+
+    /* third byte: it's the data of a REG_PRAM_SECT write */
+    g_assert(REG_PRAM_SECT <= m->cmd && m->cmd <= REG_PRAM_SECT_LAST);
+    sector = m->cmd - REG_PRAM_SECT;
+    v1s->PRAM[sector * 32 + m->alt] = m->data_out;
+    trace_via1_rtc_cmd_pram_sect_write(sector, m->alt, sector * 32 + m->alt,
+                                       m->data_out);
+    m->alt = REG_EMPTY;
+    m->cmd = REG_EMPTY;
 }
 
 static int adb_via_poll(MacVIAState *s, int state, uint8_t *data)
@@ -742,6 +847,9 @@ static void mac_via_reset(DeviceState *dev)
     v1s->next_VBL = 0;
     timer_del(v1s->one_second_timer);
     v1s->next_second = 0;
+
+    m->cmd = REG_EMPTY;
+    m->alt = REG_EMPTY;
 }
 
 static void mac_via_realize(DeviceState *dev, Error **errp)
diff --git a/hw/misc/trace-events b/hw/misc/trace-events
index 1deb1d08c1..2e0c820834 100644
--- a/hw/misc/trace-events
+++ b/hw/misc/trace-events
@@ -149,3 +149,22 @@ bcm2835_mbox_write(unsigned int size, uint64_t addr, uint64_t value) "mbox write
 bcm2835_mbox_read(unsigned int size, uint64_t addr, uint64_t value) "mbox read sz:%u addr:0x%"PRIx64" data:0x%"PRIx64
 bcm2835_mbox_irq(unsigned level) "mbox irq:ARM level:%u"
 bcm2835_mbox_property(uint32_t tag, uint32_t bufsize, size_t resplen) "mbox property tag:0x%08x in_sz:%u out_sz:%zu"
+
+# mac_via.c
+via1_rtc_update_data_out(int count, int value) "count=%d value=0x%02x"
+via1_rtc_update_data_in(int count, int value) "count=%d value=0x%02x"
+via1_rtc_internal_status(int cmd, int alt, int value) "cmd=0x%02x alt=0x%02x value=0x%02x"
+via1_rtc_internal_cmd(int cmd) "cmd=0x%02x"
+via1_rtc_cmd_invalid(int value) "value=0x%02x"
+via1_rtc_internal_time(uint32_t time) "time=0x%08x"
+via1_rtc_internal_set_cmd(int cmd) "cmd=0x%02x"
+via1_rtc_internal_ignore_cmd(int cmd) "cmd=0x%02x"
+via1_rtc_internal_set_alt(int alt, int sector, int offset) "alt=0x%02x sector=%u offset=%u"
+via1_rtc_cmd_seconds_read(int reg, int value) "reg=%d value=0x%02x"
+via1_rtc_cmd_seconds_write(int reg, int value) "reg=%d value=0x%02x"
+via1_rtc_cmd_test_write(int value) "value=0x%02x"
+via1_rtc_cmd_wprotect_write(int value) "value=0x%02x"
+via1_rtc_cmd_pram_read(int addr, int value) "addr=%u value=0x%02x"
+via1_rtc_cmd_pram_write(int addr, int value) "addr=%u value=0x%02x"
+via1_rtc_cmd_pram_sect_read(int sector, int offset, int addr, int value) "sector=%u offset=%u addr=%d value=0x%02x"
+via1_rtc_cmd_pram_sect_write(int sector, int offset, int addr, int value) "sector=%u offset=%u addr=%d value=0x%02x"
