diff --git a/hw/application_fpga/Makefile b/hw/application_fpga/Makefile
index e7ab9f4..8a27968 100644
--- a/hw/application_fpga/Makefile
+++ b/hw/application_fpga/Makefile
@@ -134,6 +134,7 @@ FIRMWARE_OBJS = \
 	$(P)/fw/tk1/partition_table.o \
 	$(P)/fw/tk1/auth_app.o \
 	$(P)/fw/tk1/rng.o \
+	$(P)/fw/tk1/reset.o \
 	$(P)/fw/tk1/preload_app.o \
 	$(P)/fw/tk1/mgmt_app.o
 
diff --git a/hw/application_fpga/fw/README.md b/hw/application_fpga/fw/README.md
index aed25a9..9058514 100644
--- a/hw/application_fpga/fw/README.md
+++ b/hw/application_fpga/fw/README.md
@@ -534,8 +534,9 @@ struct reset {
 };
 
 struct reset rst;
+uint32_t len; // Length of data in next_app_data.
 
-syscall(TK1_SYSCALL_RESET, (uint32_t)&rst, 0, 0);
+syscall(TK1_SYSCALL_RESET, (uint32_t)&rst, len, 0);
 ```
 
 Resets the TKey. Does not return.
@@ -544,7 +545,7 @@ You can pass data to the firmware about the reset type `type` and a
 digest that the next app must have. You can also leave some data to
 the next app in the chain in `next_app_data`.
 
-The types of the reset are defined in `resetinfo.h`:
+The types of the reset are defined in `reset.h`:
 
 | *Name*             | *Comment*                                      |
 |--------------------|------------------------------------------------|
diff --git a/hw/application_fpga/fw/reset_test/main.c b/hw/application_fpga/fw/reset_test/main.c
index 154e24d..2be91cb 100644
--- a/hw/application_fpga/fw/reset_test/main.c
+++ b/hw/application_fpga/fw/reset_test/main.c
@@ -13,7 +13,7 @@
 
 #include "../testapp/syscall.h"
 #include "../tk1/proto.h"
-#include "../tk1/resetinfo.h"
+#include "../tk1/reset.h"
 #include "../tk1/syscall_num.h"
 
 // Converts a single hex character to its integer value
diff --git a/hw/application_fpga/fw/testapp/main.c b/hw/application_fpga/fw/testapp/main.c
index 5619ebd..be4e6bc 100644
--- a/hw/application_fpga/fw/testapp/main.c
+++ b/hw/application_fpga/fw/testapp/main.c
@@ -11,7 +11,7 @@
 #include <tkey/tk1_mem.h>
 
 #include "../tk1/proto.h"
-#include "../tk1/resetinfo.h"
+#include "../tk1/reset.h"
 #include "../tk1/syscall_num.h"
 #include "syscall.h"
 
diff --git a/hw/application_fpga/fw/testloadapp/main.c b/hw/application_fpga/fw/testloadapp/main.c
index 01dbd8b..f3ccd3c 100644
--- a/hw/application_fpga/fw/testloadapp/main.c
+++ b/hw/application_fpga/fw/testloadapp/main.c
@@ -7,7 +7,7 @@
 #include <tkey/tk1_mem.h>
 
 #include "../testapp/syscall.h"
-#include "../tk1/resetinfo.h"
+#include "../tk1/reset.h"
 #include "../tk1/syscall_num.h"
 #include "blink.h"
 #include "tkey/assert.h"
diff --git a/hw/application_fpga/fw/tk1/main.c b/hw/application_fpga/fw/tk1/main.c
index 3cbcc1f..ae577af 100644
--- a/hw/application_fpga/fw/tk1/main.c
+++ b/hw/application_fpga/fw/tk1/main.c
@@ -17,7 +17,7 @@
 #include "partition_table.h"
 #include "preload_app.h"
 #include "proto.h"
-#include "resetinfo.h"
+#include "reset.h"
 #include "state.h"
 #include "syscall_enable.h"
 
diff --git a/hw/application_fpga/fw/tk1/reset.c b/hw/application_fpga/fw/tk1/reset.c
new file mode 100644
index 0000000..4f37429
--- /dev/null
+++ b/hw/application_fpga/fw/tk1/reset.c
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2025 - Tillitis AB
+ * SPDX-License-Identifier: GPL-2.0-only
+ */
+
+#include <stdint.h>
+#include <tkey/assert.h>
+#include <tkey/lib.h>
+#include <tkey/tk1_mem.h>
+
+#include "reset.h"
+
+// clang-format off
+static volatile uint32_t *system_reset  = (volatile uint32_t *)TK1_MMIO_TK1_SYSTEM_RESET;
+static volatile struct reset *resetinfo = (volatile struct reset *)TK1_MMIO_RESETINFO_BASE;
+// clang-format on
+
+int reset(struct reset *userreset, size_t nextlen)
+{
+	if ((uint32_t)userreset < TK1_RAM_BASE ||
+	    (uint32_t)userreset >= TK1_RAM_BASE + TK1_RAM_SIZE) {
+		return -1;
+	}
+
+	if (nextlen > sizeof(resetinfo->next_app_data)) {
+		return -1;
+	}
+
+	(void)memset((void *)resetinfo, 0, sizeof(*resetinfo));
+	resetinfo->type = userreset->type;
+	memcpy((void *)resetinfo->app_digest, userreset->app_digest, 32);
+	memcpy((void *)resetinfo->next_app_data, userreset->next_app_data,
+	       nextlen);
+
+	// Do the actual reset.
+	*system_reset = 1;
+
+	// Should not be reached.
+	assert(1 == 2);
+
+	__builtin_unreachable();
+}
diff --git a/hw/application_fpga/fw/tk1/resetinfo.h b/hw/application_fpga/fw/tk1/reset.h
similarity index 82%
rename from hw/application_fpga/fw/tk1/resetinfo.h
rename to hw/application_fpga/fw/tk1/reset.h
index 0a26ace..a434d38 100644
--- a/hw/application_fpga/fw/tk1/resetinfo.h
+++ b/hw/application_fpga/fw/tk1/reset.h
@@ -1,9 +1,10 @@
 // Copyright (C) 2025 - Tillitis AB
 // SPDX-License-Identifier: GPL-2.0-only
 
-#ifndef TKEY_RESETINFO_H
-#define TKEY_RESETINFO_H
+#ifndef TKEY_RESET_H
+#define TKEY_RESET_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 #define TK1_MMIO_RESETINFO_BASE 0xd0000f00
@@ -25,4 +26,5 @@ struct reset {
 	uint8_t next_app_data[220]; // Data to leave around for next app
 };
 
+int reset(struct reset *userreset, size_t nextlen);
 #endif
diff --git a/hw/application_fpga/fw/tk1/syscall_handler.c b/hw/application_fpga/fw/tk1/syscall_handler.c
index a042966..18bba35 100644
--- a/hw/application_fpga/fw/tk1/syscall_handler.c
+++ b/hw/application_fpga/fw/tk1/syscall_handler.c
@@ -13,13 +13,11 @@
 #include "preload_app.h"
 #include "storage.h"
 
-#include "../tk1/resetinfo.h"
+#include "../tk1/reset.h"
 #include "../tk1/syscall_num.h"
 
 // clang-format off
-static volatile uint32_t *system_reset  = (volatile uint32_t *)TK1_MMIO_TK1_SYSTEM_RESET;
 static volatile uint32_t *udi           = (volatile uint32_t *)TK1_MMIO_TK1_UDI_FIRST;
-static volatile struct reset *resetinfo = (volatile struct reset *)TK1_MMIO_RESETINFO_BASE;
 // clang-format on
 
 extern struct partition_table_storage part_table_storage;
@@ -29,32 +27,9 @@ int32_t syscall_handler(uint32_t number, uint32_t arg1, uint32_t arg2,
 			uint32_t arg3)
 {
 	switch (number) {
-	case TK1_SYSCALL_RESET: {
-		struct reset *userreset;
-
-		if (arg1 < TK1_RAM_BASE ||
-		    arg1 >= TK1_RAM_BASE + TK1_RAM_SIZE) {
-			return -1;
-		}
-
-		userreset = (struct reset *)arg1;
-
-		if (arg2 > sizeof(resetinfo->next_app_data)) {
-			return -1;
-		}
-
-		(void)memset((void *)resetinfo, 0, sizeof(*resetinfo));
-		resetinfo->type = userreset->type;
-		memcpy((void *)resetinfo->app_digest, userreset->app_digest,
-		       32);
-		memcpy((void *)resetinfo->next_app_data,
-		       userreset->next_app_data, arg2);
-		*system_reset = 1;
-
-		// Should not be reached.
-		assert(1 == 2);
+	case TK1_SYSCALL_RESET:
+		reset((struct reset *)arg1, (size_t)arg2);
 		break;
-	}
 
 	case TK1_SYSCALL_ALLOC_AREA:
 		if (storage_allocate_area(&part_table_storage) < 0) {