diff --git a/include/ovni.h.in b/include/ovni.h.in
index 237f63c..067e97f 100644
--- a/include/ovni.h.in
+++ b/include/ovni.h.in
@@ -143,7 +143,10 @@ char *ovni_attr_get_json(const char *key);
 void ovni_attr_flush(void);
 
 /* Mark */
-void ovni_mark_type(int32_t type, const char *title);
+enum ovni_mark_flags {
+	OVNI_MARK_STACK = 1, /*< Use push/pop instead of set */
+};
+void ovni_mark_type(int32_t type, long flags, const char *title);
 void ovni_mark_label(int32_t type, int64_t value, const char *label);
 void ovni_mark_push(int32_t type, int64_t value);
 void ovni_mark_pop(int32_t type, int64_t value);
diff --git a/src/emu/CMakeLists.txt b/src/emu/CMakeLists.txt
index a655d84..97d696b 100644
--- a/src/emu/CMakeLists.txt
+++ b/src/emu/CMakeLists.txt
@@ -49,6 +49,7 @@ add_library(emu STATIC
   value.c
   ovni/event.c
   ovni/setup.c
+  ovni/mark.c
   nanos6/setup.c
   nanos6/event.c
   nanos6/breakdown.c
diff --git a/src/emu/ovni/event.c b/src/emu/ovni/event.c
index 338f48e..9f83844 100644
--- a/src/emu/ovni/event.c
+++ b/src/emu/ovni/event.c
@@ -16,6 +16,7 @@
 #include "proc.h"
 #include "thread.h"
 #include "value.h"
+#include "mark.h"
 
 static int
 pre_thread_execute(struct emu *emu, struct thread *th)
@@ -478,8 +479,7 @@ model_ovni_event(struct emu *emu)
 			/* Ignore sorting events */
 			return 0;
 		case 'M':
-			/* TODO: Ignore mark events for now */
-			return 0;
+			return mark_event(emu);
 		default:
 			err("unknown ovni event category %c",
 					emu->ev->c);
diff --git a/src/emu/ovni/mark.c b/src/emu/ovni/mark.c
new file mode 100644
index 0000000..184a944
--- /dev/null
+++ b/src/emu/ovni/mark.c
@@ -0,0 +1,259 @@
+#include "mark.h"
+
+#include "chan.h"
+#include "emu.h"
+#include "emu_ev.h"
+#include "emu_prv.h"
+#include "ovni.h"
+#include "ovni_priv.h"
+#include "parson.h"
+#include "pv/pcf.h"
+#include "thread.h"
+#include "uthash.h"
+#include <errno.h>
+
+struct mark_value {
+	int32_t type;
+	char title[MAX_PCF_LABEL];
+	struct chan ch;
+	struct pcf_type *pcftype;
+	UT_hash_handle hh; /* Indexed by type */
+};
+
+struct mark_chan {
+	long type;
+	char title[MAX_PCF_LABEL];
+	struct chan ch;
+	UT_hash_handle hh; /* Indexed by type */
+};
+
+static int
+parse_labels(struct mark_chan *c, JSON_Object *labels)
+{
+	UNUSED(c);
+	UNUSED(labels);
+
+	/* TODO: Implement */
+
+	return 0;
+}
+
+static struct mark_chan *
+find_mark_chan(struct ovni_mark_emu *m, long type)
+{
+	struct mark_chan *c;
+	HASH_FIND_LONG(m->chan, &type, c);
+	return c;
+}
+
+static struct mark_chan *
+create_mark_chan(struct ovni_mark_emu *m, long type, const char *chan_type, const char *title)
+{
+	struct mark_chan *c = find_mark_chan(m, type);
+
+	if (c != NULL) {
+		err("mark type %d already defined", type);
+		return NULL;
+	}
+
+	c = calloc(1, sizeof(*c));
+	if (c == NULL) {
+		err("calloc failed:");
+		return NULL;
+	}
+
+	c->type = type;
+
+	int len = snprintf(c->title, MAX_PCF_LABEL, "%s", title);
+	if (len >= MAX_PCF_LABEL) {
+		err("mark title too long: %s", title);
+		return NULL;
+	}
+
+	enum chan_type ctype;
+	if (strcmp(chan_type, "single") == 0) {
+		ctype = CHAN_SINGLE;
+	} else if (strcmp(chan_type, "stack") == 0) {
+		ctype = CHAN_STACK;
+	} else {
+		err("chan_type %s not understood", chan_type);
+		return NULL;
+	}
+
+	chan_init(&c->ch, ctype, "mark%ld", type);
+
+	HASH_ADD_LONG(m->chan, type, c);
+
+	return c;
+}
+
+static int
+parse_mark(struct ovni_mark_emu *m, const char *typestr, JSON_Value *markval)
+{
+	errno = 0;
+	char *endptr = NULL;
+	long type = strtol(typestr, &endptr, 10);
+
+	if (errno != 0 || endptr == typestr || endptr[0] != '\0') {
+		err("failed to parse type number: %s", typestr);
+		return -1;
+	}
+
+	if (type < 0 || type >= 100) {
+		err("mark type should be in [0, 100) range: %ld", type);
+		return -1;
+	}
+
+	JSON_Object *mark = json_value_get_object(markval);
+	if (mark == NULL) {
+		err("json_value_get_object() failed");
+		return -1;
+	}
+
+	const char *title = json_object_get_string(mark, "title");
+	if (title == NULL) {
+		err("json_object_get_string() for title failed");
+		return -1;
+	}
+
+	const char *chan_type = json_object_get_string(mark, "chan_type");
+	if (chan_type == NULL) {
+		err("json_object_get_string() for chan_type failed");
+		return -1;
+	}
+
+	JSON_Object *labels = json_object_get_object(mark, "labels");
+	if (labels == NULL) {
+		err("json_object_get_object() for labels failed");
+		return -1;
+	}
+
+	struct mark_chan *c = find_mark_chan(m, type);
+	if (c == NULL) {
+		c = create_mark_chan(m, type, chan_type, title);
+		if (c == NULL) {
+			err("cannot create mark chan");
+			return -1;
+		}
+	} else {
+		/* It may already exist as defined by other threads, so ensure
+		 * they have the same title. */
+		if (strcmp(c->title, title) != 0) {
+			err("mark with type %ld already registered with another title", type);
+			err(" old: %s", c->title);
+			err(" new: %s", title);
+			return -1;
+		}
+	}
+
+	/* Now populate the mark channel with all value labels */
+
+	if (parse_labels(c, labels) != 0) {
+		err("cannot parse labels");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int
+scan_thread(struct ovni_mark_emu *memu, struct thread *t)
+{
+	JSON_Object *obj = json_object_dotget_object(t->meta, "ovni.mark");
+
+	/* No marks in this thread */
+	if (obj == NULL)
+		return 0;
+
+	memu->has_marks = 1;
+
+	size_t n = json_object_get_count(obj);
+	for (size_t i = 0; i < n; i++) {
+		const char *typestr = json_object_get_name(obj, i);
+		if (typestr == NULL) {
+			err("json_object_get_name failed");
+			return -1;
+		}
+		JSON_Value *markval = json_object_get_value_at(obj, i);
+		if (markval == NULL) {
+			err("json_object_get_value_at failed");
+			return -1;
+		}
+
+		if (parse_mark(memu, typestr, markval) != 0) {
+			err("cannot parse mark");
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+/* Scans streams for marks and creates the mark channels */
+int
+mark_create(struct emu *emu)
+{
+	struct ovni_emu *oemu = EXT(emu, 'O');
+	struct ovni_mark_emu *memu = &oemu->mark;
+
+	memset(memu, 0, sizeof(*memu));
+
+	for (struct thread *th = emu->system.threads; th; th = th->gnext) {
+		if (scan_thread(memu, th) != 0) {
+			err("scan_thread failed");
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+/* Connect the channels to the output PVTs */
+int
+mark_connect(struct emu *emu)
+{
+	UNUSED(emu);
+
+	/* TODO: Implement */
+
+	return 0;
+}
+
+int
+mark_event(struct emu *emu)
+{
+	if (emu->ev->payload_size != 8 + 4) {
+		err("unexpected payload size %d", emu->ev->payload_size);
+		return -1;
+	}
+
+	struct ovni_emu *oemu = EXT(emu, 'O');
+	struct ovni_mark_emu *memu = &oemu->mark;
+
+	int64_t value = emu->ev->payload->i64[0];
+	long type = (long) emu->ev->payload->i32[2]; /* always fits */
+
+	struct mark_chan *mc = find_mark_chan(memu, type);
+
+	if (mc == NULL) {
+		err("cannot find mark with type %ld", type);
+		return -1;
+	}
+
+	/* TODO: Remove stub */
+	//struct chan *ch = &mc->ch;
+
+	switch (emu->ev->v) {
+		case '[':
+			//return chan_push(ch, value_int64(value));
+			info("chan_push(ch, value_int64(%ld))", value);
+			return 0;
+		case ']':
+			//return chan_pop(ch, value_int64(value));
+			info("chan_pop(ch, value_int64(%ld))", value);
+			return 0;
+		default:
+			err("unknown mark event value %c", emu->ev->v);
+			return -1;
+	}
+}
diff --git a/src/emu/ovni/mark.h b/src/emu/ovni/mark.h
new file mode 100644
index 0000000..7a4cb8d
--- /dev/null
+++ b/src/emu/ovni/mark.h
@@ -0,0 +1,19 @@
+#ifndef MARK_H
+#define MARK_H
+
+#include "common.h"
+
+struct emu;
+struct mark_chan;
+
+struct ovni_mark_emu {
+	/* Hash table of channels */
+	struct mark_chan *chan;
+	int has_marks;
+};
+
+USE_RET int mark_create(struct emu *emu);
+USE_RET int mark_connect(struct emu *emu);
+USE_RET int mark_event(struct emu *emu);
+
+#endif /* MARK_H */
diff --git a/src/emu/ovni/ovni_priv.h b/src/emu/ovni/ovni_priv.h
index c5d2ccd..9e68d7c 100644
--- a/src/emu/ovni/ovni_priv.h
+++ b/src/emu/ovni/ovni_priv.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2021-2023 Barcelona Supercomputing Center (BSC)
+/* Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #ifndef OVNI_PRIV_H
@@ -10,6 +10,7 @@
  * execution by the kernel. */
 
 #include "emu.h"
+#include "mark.h"
 #include "model_cpu.h"
 #include "model_thread.h"
 #include <stdint.h>
@@ -39,6 +40,10 @@ struct ovni_cpu {
 	struct model_cpu m;
 };
 
+struct ovni_emu {
+	struct ovni_mark_emu mark;
+};
+
 int model_ovni_probe(struct emu *emu);
 int model_ovni_create(struct emu *emu);
 int model_ovni_connect(struct emu *emu);
diff --git a/src/emu/ovni/setup.c b/src/emu/ovni/setup.c
index 84be469..7d2f2f1 100644
--- a/src/emu/ovni/setup.c
+++ b/src/emu/ovni/setup.c
@@ -7,6 +7,7 @@
 #include "emu.h"
 #include "emu_prv.h"
 #include "ev_spec.h"
+#include "mark.h"
 #include "model.h"
 #include "model_chan.h"
 #include "model_cpu.h"
@@ -178,6 +179,19 @@ model_ovni_create(struct emu *emu)
 		return -1;
 	}
 
+	struct ovni_emu *oemu = calloc(1, sizeof(*oemu));
+	if (oemu == NULL) {
+		err("calloc failed:");
+		return -1;
+	}
+
+	extend_set(&emu->ext, 'O', oemu);
+
+	if (mark_create(emu) != 0) {
+		err("mark_create failed");
+		return -1;
+	}
+
 	return 0;
 }
 
diff --git a/src/rt/ovni.c b/src/rt/ovni.c
index 3c6d7ec..cab83eb 100644
--- a/src/rt/ovni.c
+++ b/src/rt/ovni.c
@@ -1067,7 +1067,7 @@ ovni_attr_flush(void)
 
 /** creates a new mark type. */
 void
-ovni_mark_type(int32_t type, const char *title)
+ovni_mark_type(int32_t type, long flags, const char *title)
 {
 	if (type < 0 || type >= 100)
 		die("type must be in [0,100) range");
@@ -1089,7 +1089,14 @@ ovni_mark_type(int32_t type, const char *title)
 		die("title key too long");
 
 	if (json_object_dotset_string(meta, key, title) != 0)
-		die("json_object_dotset_string() failed", type);
+		die("json_object_dotset_string() failed for title");
+
+	const char *chan_type = flags & OVNI_MARK_STACK ? "stack" : "single";
+	if (snprintf(key, 128, "ovni.mark.%"PRId32".chan_type", type) >= 128)
+		die("chan_type key too long");
+
+	if (json_object_dotset_string(meta, key, chan_type) != 0)
+		die("json_object_dotset_string() failed for chan_type");
 }
 
 /** creates a new mark type. */
diff --git a/test/emu/ovni/libovni-mark.c b/test/emu/ovni/libovni-mark.c
index 25a167c..3dd5d55 100644
--- a/test/emu/ovni/libovni-mark.c
+++ b/test/emu/ovni/libovni-mark.c
@@ -18,7 +18,7 @@ main(void)
 {
 	instr_start(0, 1);
 
-	ovni_mark_type(MARK_COLORS, "Colors");
+	ovni_mark_type(MARK_COLORS, OVNI_MARK_STACK, "Colors");
 
 	if(!ovni_attr_has("ovni.mark.1.title"))
 		die("missing mark title");