diff --git a/src/emu/cpu.c b/src/emu/cpu.c
index 85d15b8..bd3edf0 100644
--- a/src/emu/cpu.c
+++ b/src/emu/cpu.c
@@ -26,6 +26,12 @@ static int chan_type[] = {
 	[CPU_CHAN_THACT] = -1,
 };
 
+static long chan_flags[] = {
+	[CPU_CHAN_PID]  = PRV_SKIPDUP,
+	[CPU_CHAN_TID]  = PRV_SKIPDUP,
+	[CPU_CHAN_NRUN] = PRV_SKIPDUP | PRV_ZERO,
+};
+
 void
 cpu_init_begin(struct cpu *cpu, int index, int phyid, int is_virtual)
 {
@@ -148,7 +154,8 @@ cpu_connect(struct cpu *cpu, struct bay *bay, struct recorder *rec)
 			continue;
 
 		long row = cpu->gindex;
-		if (prv_register(prv, row, type, bay, c, PRV_DUP)) {
+		long flags = chan_flags[i];
+		if (prv_register(prv, row, type, bay, c, flags)) {
 			err("prv_register failed");
 			return -1;
 		}
diff --git a/src/emu/kernel/setup.c b/src/emu/kernel/setup.c
index f3d950f..02a723a 100644
--- a/src/emu/kernel/setup.c
+++ b/src/emu/kernel/setup.c
@@ -41,10 +41,15 @@ static const struct pcf_value_label (*pcf_labels[CH_MAX])[] = {
 	[CH_CS] = &kernel_cs_values,
 };
 
+static const long prv_flags[CH_MAX] = {
+	[CH_CS] = PRV_SKIPDUP,
+};
+
 static const struct model_pvt_spec pvt_spec = {
 	.type = pvt_type,
 	.prefix = pcf_prefix,
 	.label = pcf_labels,
+	.flags = prv_flags,
 };
 
 /* ----------------- tracking ------------------ */
diff --git a/src/emu/model_pvt.c b/src/emu/model_pvt.c
index 89a19ad..21b6267 100644
--- a/src/emu/model_pvt.c
+++ b/src/emu/model_pvt.c
@@ -75,11 +75,13 @@ connect_cpu_prv(struct emu *emu, struct cpu *scpu, struct prv *prv, int id)
 {
 	struct model_cpu *cpu = EXT(scpu, id);
 	const struct model_chan_spec *spec = cpu->spec->chan;
+	const long *flags_arr = spec->pvt->flags;
 	for (int i = 0; i < spec->nch; i++) {
 		struct chan *out = track_get_output(&cpu->track[i]);
 		long type = spec->pvt->type[i];
 		long row = scpu->gindex;
-		if (prv_register(prv, row, type, &emu->bay, out, PRV_DUP)) {
+		long flags = flags_arr ? flags_arr[i] : 0;
+		if (prv_register(prv, row, type, &emu->bay, out, flags)) {
 			err("prv_register failed");
 			return -1;
 		}
@@ -125,11 +127,13 @@ connect_thread_prv(struct emu *emu, struct thread *sth, struct prv *prv, int id)
 {
 	struct model_thread *th = EXT(sth, id);
 	const struct model_chan_spec *spec = th->spec->chan;
+	const long *flags_arr = spec->pvt->flags;
 	for (int i = 0; i < spec->nch; i++) {
 		struct chan *out = track_get_output(&th->track[i]);
 		long type = spec->pvt->type[i];
 		long row = sth->gindex;
-		if (prv_register(prv, row, type, &emu->bay, out, PRV_DUP)) {
+		long flags = flags_arr ? flags_arr[i] : 0;
+		if (prv_register(prv, row, type, &emu->bay, out, flags)) {
 			err("prv_register failed");
 			return -1;
 		}
diff --git a/src/emu/model_pvt.h b/src/emu/model_pvt.h
index f9cfb85..a944488 100644
--- a/src/emu/model_pvt.h
+++ b/src/emu/model_pvt.h
@@ -11,6 +11,7 @@ struct model_pvt_spec {
 	const int *type;
 	const char **prefix;
 	const char **suffix;
+	const long *flags;
 	const struct pcf_value_label (**label)[];
 };
 
diff --git a/src/emu/nanos6/setup.c b/src/emu/nanos6/setup.c
index eff5061..1193dc2 100644
--- a/src/emu/nanos6/setup.c
+++ b/src/emu/nanos6/setup.c
@@ -92,10 +92,19 @@ static const struct pcf_value_label (*pcf_labels[CH_MAX])[] = {
 	[CH_THREAD]    = &nanos6_thread_type,
 };
 
+static const long prv_flags[CH_MAX] = {
+	[CH_TASKID]    = PRV_SKIPDUP,
+	[CH_TYPE]      = PRV_SKIPDUP,
+	[CH_SUBSYSTEM] = PRV_SKIPDUP,
+	[CH_RANK]      = PRV_SKIPDUP,
+	[CH_THREAD]    = PRV_SKIPDUP,
+};
+
 static const struct model_pvt_spec pvt_spec = {
 	.type = pvt_type,
 	.prefix = pcf_prefix,
 	.label = pcf_labels,
+	.flags = prv_flags,
 };
 
 /* ----------------- tracking ------------------ */
diff --git a/src/emu/nodes/setup.c b/src/emu/nodes/setup.c
index 7cfcb4c..8f5b337 100644
--- a/src/emu/nodes/setup.c
+++ b/src/emu/nodes/setup.c
@@ -49,10 +49,15 @@ static const struct pcf_value_label (*pcf_labels[CH_MAX])[] = {
 	[CH_SUBSYSTEM] = &nodes_ss_values,
 };
 
+static const long prv_flags[CH_MAX] = {
+	[CH_SUBSYSTEM] = PRV_SKIPDUP,
+};
+
 static const struct model_pvt_spec pvt_spec = {
 	.type = pvt_type,
 	.prefix = pcf_prefix,
 	.label = pcf_labels,
+	.flags = prv_flags,
 };
 
 /* ----------------- tracking ------------------ */
diff --git a/src/emu/nosv/setup.c b/src/emu/nosv/setup.c
index edad404..6f53447 100644
--- a/src/emu/nosv/setup.c
+++ b/src/emu/nosv/setup.c
@@ -75,10 +75,37 @@ static const struct pcf_value_label (*pcf_labels[CH_MAX])[] = {
 	[CH_SUBSYSTEM] = &nosv_ss_values,
 };
 
-static const struct model_pvt_spec pvt_spec = {
+/* ------------- duplicates in prv -------------- */
+
+static const long th_prv_flags[CH_MAX] = {
+	/* Due muxes we need to skip duplicated nulls */
+	[CH_TASKID]    = PRV_SKIPDUP,
+	[CH_TYPE]      = PRV_SKIPDUP,
+	[CH_APPID]     = PRV_SKIPDUP,
+	[CH_SUBSYSTEM] = PRV_SKIPDUP,
+	[CH_RANK]      = PRV_SKIPDUP,
+};
+
+static const long cpu_prv_flags[CH_MAX] = {
+	[CH_TASKID]    = PRV_SKIPDUP,
+	[CH_TYPE]      = PRV_SKIPDUP,
+	[CH_APPID]     = PRV_SKIPDUP,
+	[CH_SUBSYSTEM] = PRV_SKIPDUP,
+	[CH_RANK]      = PRV_SKIPDUP,
+};
+
+static const struct model_pvt_spec th_pvt_spec = {
 	.type = pvt_type,
 	.prefix = pcf_prefix,
 	.label = pcf_labels,
+	.flags = th_prv_flags,
+};
+
+static const struct model_pvt_spec cpu_pvt_spec = {
+	.type = pvt_type,
+	.prefix = pcf_prefix,
+	.label = pcf_labels,
+	.flags = cpu_prv_flags,
 };
 
 /* ----------------- tracking ------------------ */
@@ -107,7 +134,7 @@ static const struct model_chan_spec th_chan = {
 	.ch_names = chan_name,
 	.ch_stack = chan_stack,
 	.ch_dup = chan_dup,
-	.pvt = &pvt_spec,
+	.pvt = &th_pvt_spec,
 	.track = th_track,
 };
 
@@ -116,24 +143,24 @@ static const struct model_chan_spec cpu_chan = {
 	.prefix = model_name,
 	.ch_names = chan_name,
 	.ch_stack = chan_stack,
-	.pvt = &pvt_spec,
+	.pvt = &cpu_pvt_spec,
 	.track = cpu_track,
 };
 
 /* ----------------- models ------------------ */
 
-static const struct model_cpu_spec cpu_spec = {
-	.size = sizeof(struct nosv_cpu),
-	.chan = &cpu_chan,
-	.model = &model_nosv,
-};
-
 static const struct model_thread_spec th_spec = {
 	.size = sizeof(struct nosv_thread),
 	.chan = &th_chan,
 	.model = &model_nosv,
 };
 
+static const struct model_cpu_spec cpu_spec = {
+	.size = sizeof(struct nosv_cpu),
+	.chan = &cpu_chan,
+	.model = &model_nosv,
+};
+
 /* ----------------------------------------------------- */
 
 int
diff --git a/src/emu/ovni/setup.c b/src/emu/ovni/setup.c
index bf78da4..36a335c 100644
--- a/src/emu/ovni/setup.c
+++ b/src/emu/ovni/setup.c
@@ -40,10 +40,15 @@ static const struct pcf_value_label (*pcf_labels[CH_MAX])[] = {
 	[CH_FLUSH] = &flushing_values,
 };
 
+static const long prv_flags[CH_MAX] = {
+	[CH_FLUSH] = PRV_SKIPDUP,
+};
+
 static const struct model_pvt_spec pvt_spec = {
 	.type = pvt_type,
 	.prefix = pcf_prefix,
 	.label = pcf_labels,
+	.flags = prv_flags,
 };
 
 /* ----------------- tracking ------------------ */
diff --git a/src/emu/pv/prv.c b/src/emu/pv/prv.c
index 7d7c34b..a5e5ad7 100644
--- a/src/emu/pv/prv.c
+++ b/src/emu/pv/prv.c
@@ -67,16 +67,20 @@ find_prv_chan(struct prv *prv, long id)
 	return rchan;
 }
 
-static int
+static void
 write_line(struct prv *prv, long row_base1, long type, long value)
 {
-	int ret = fprintf(prv->file, "2:0:1:1:%ld:%ld:%ld:%ld\n",
+	fprintf(prv->file, "2:0:1:1:%ld:%ld:%ld:%ld\n",
 			row_base1, prv->time, type, value);
+}
 
-	if (ret < 0)
-		return -1;
-	else
+static int
+is_value_dup(struct prv_chan *rchan, struct value *value)
+{
+	if (!rchan->last_value_set)
 		return 0;
+
+	return value_is_equal(value, &rchan->last_value);
 }
 
 static int
@@ -90,18 +94,25 @@ emit(struct prv *prv, struct prv_chan *rchan)
 		return -1;
 	}
 
-	/* Ensure we don't emit the same value twice */
-	if (rchan->last_value_set && value_is_equal(&value, &rchan->last_value)) {
-		char buf[128];
-		if (rchan->flags & PRV_DUP) {
-			dbg("skipping duplicated value %s for channel %s\n",
-					value_str(value, buf), chan->name);
-			return 0;
-		} else {
+	/* Only test for duplicates if not emitting them */
+	if (~rchan->flags & PRV_EMITDUP) {
+		int is_dup = is_value_dup(rchan, &value);
+		if (is_dup) {
+			if (rchan->flags & PRV_SKIPDUP)
+				return 0;
+
+			int is_null = value_is_null(value);
+			if (rchan->flags & PRV_SKIPNULL && is_null)
+				return 0;
+
 			err("error duplicated value %s for channel %s\n",
 					value_str(value, buf), chan->name);
 			return -1;
 		}
+
+		/* Only set when caring about duplicates */
+		rchan->last_value = value;
+		rchan->last_value_set = 1;
 	}
 
 	long val = 0;
@@ -111,12 +122,12 @@ emit(struct prv *prv, struct prv_chan *rchan)
 			if (rchan->flags & PRV_NEXT)
 				val++;
 
-			//if (val == 0) {
-			//	err("forbidden value 0 in %s: %s\n",
-			//			chan->name,
-			//			value_str(value, buf));
-			//	return -1;
-			//}
+			if (~rchan->flags & PRV_ZERO && val == 0) {
+				err("forbidden value 0 in %s: %s\n",
+						chan->name,
+						value_str(value, buf));
+				return -1;
+			}
 			break;
 		case VALUE_NULL:
 			val = 0;
@@ -127,16 +138,10 @@ emit(struct prv *prv, struct prv_chan *rchan)
 			return -1;
 	}
 
-	if (write_line(prv, rchan->row_base1, rchan->type, val) != 0) {
-		err("write_line failed for channel %s\n",
-				chan->name);
-		return -1;
-	}
+	write_line(prv, rchan->row_base1, rchan->type, val);
 
 	dbg("written %s for chan %s", value_str(value, buf), chan->name);
 
-	rchan->last_value = value;
-	rchan->last_value_set = 1;
 
 	return 0;
 }
diff --git a/src/emu/pv/prv.h b/src/emu/pv/prv.h
index f7da314..86af7f7 100644
--- a/src/emu/pv/prv.h
+++ b/src/emu/pv/prv.h
@@ -12,8 +12,11 @@
 struct prv;
 
 enum prv_flags {
-	PRV_DUP = 1<<0,
-	PRV_NEXT = 1<<1, /* Add one to the channel value */
+	PRV_EMITDUP  = 1<<0, /* Emit duplicates (no error, emit) */
+	PRV_SKIPDUP  = 1<<1, /* Skip duplicates (no error, no emit) */
+	PRV_SKIPNULL = 1<<2, /* Skip null duplicates (no error, no emit) */
+	PRV_NEXT     = 1<<3, /* Add one to the channel value */
+	PRV_ZERO     = 1<<4, /* Value 0 is allowed */
 };
 
 struct prv_chan {
diff --git a/src/emu/thread.c b/src/emu/thread.c
index 12a62e0..3b320fd 100644
--- a/src/emu/thread.c
+++ b/src/emu/thread.c
@@ -9,20 +9,26 @@
 
 static const char chan_fmt[] = "thread%lu.%s";
 static const char *chan_name[] = {
-	[TH_CHAN_CPU] = "cpu_gindex",
-	[TH_CHAN_TID] = "tid_active",
+	[TH_CHAN_CPU]   = "cpu_gindex",
+	[TH_CHAN_TID]   = "tid_active",
 	[TH_CHAN_STATE] = "state",
 };
 
 static const int chan_type[] = {
-	[TH_CHAN_TID] = 2,
+	[TH_CHAN_CPU]   = 6,
+	[TH_CHAN_TID]   = 2,
 	[TH_CHAN_STATE] = 4,
-	[TH_CHAN_CPU] = 6,
+};
+
+static const long prv_flags[] = {
+	[TH_CHAN_CPU]   = PRV_SKIPDUP | PRV_NEXT, /* Add one to the cpu gindex */
+	[TH_CHAN_TID]   = PRV_SKIPDUP,
+	[TH_CHAN_STATE] = PRV_SKIPDUP,
 };
 
 static const char *pvt_name[] = {
-	[TH_CHAN_CPU] = "Thread: CPU affinity",
-	[TH_CHAN_TID] = "Thread: TID of the ACTIVE thread",
+	[TH_CHAN_CPU]   = "Thread: CPU affinity",
+	[TH_CHAN_TID]   = "Thread: TID of the ACTIVE thread",
 	[TH_CHAN_STATE] = "Thread: thread state",
 };
 
@@ -201,11 +207,7 @@ thread_connect(struct thread *th, struct bay *bay, struct recorder *rec)
 
 		long type = chan_type[i];
 		long row = th->gindex;
-		long flags = PRV_DUP;
-
-		/* Add one to the cpu gindex in the PRV output */
-		if (i == TH_CHAN_CPU)
-			flags |= PRV_NEXT;
+		long flags = prv_flags[i];
 
 		if (prv_register(prv, row, type, bay, c, flags)) {
 			err("prv_register failed");