diff --git a/hw/application_fpga/apps/Makefile b/hw/application_fpga/apps/Makefile
index b8ce38c..a43b6cf 100644
--- a/hw/application_fpga/apps/Makefile
+++ b/hw/application_fpga/apps/Makefile
@@ -41,7 +41,7 @@ LDFLAGS = \
 	-L $(LIBDIR) -lcrt0 -lcommon -lmonocypher -lblake2s
 
 .PHONY: all
-all: defaultapp.bin reset_test.bin testapp.bin testloadapp.bin
+all: defaultapp.bin loopbackapp.bin reset_test.bin testapp.bin testloadapp.bin
 
 # Turn elf into bin for device
 %.bin: %.elf
@@ -66,6 +66,14 @@ DEFAULTAPP_OBJS = \
 defaultapp.elf: tkey-libs $(OBJS) $(DEFAULTAPP_OBJS)
 	$(CC) $(CFLAGS) $(OBJS) $(DEFAULTAPP_OBJS) $(LDFLAGS) -o $@
 
+# loopbackapp
+
+LOOPBACKAPP_OBJS = \
+	$(P)/loopbackapp/main.o
+
+loopbackapp.elf: tkey-libs $(LOOPBACKAPP_OBJS)
+	$(CC) $(CFLAGS) $(LOOPBACKAPP_OBJS) $(LDFLAGS) -o $@
+
 # reset_test
 
 RESET_TEST_FMTFILES = *.[ch]
@@ -97,6 +105,9 @@ fmt:
 	clang-format --dry-run --ferror-limit=0 defaultapp/*.[ch]
 	clang-format --verbose -i defaultapp/*.[ch]
 
+	clang-format --dry-run --ferror-limit=0 loopbackapp/*.[ch]
+	clang-format --verbose -i loopbackapp/*.[ch]
+
 	clang-format --dry-run --ferror-limit=0 reset_test/*.[ch]
 	clang-format --verbose -i reset_test/*.[ch]
 
@@ -110,6 +121,8 @@ fmt:
 checkfmt:
 	clang-format --dry-run --ferror-limit=0 defaultapp/*.[ch]
 
+	clang-format --dry-run --ferror-limit=0 loopbackapp/*.[ch]
+
 	clang-format --dry-run --ferror-limit=0 reset_test/*.[ch]
 
 	clang-format --dry-run --ferror-limit=0 testapp/*.[ch]
@@ -118,6 +131,6 @@ checkfmt:
 
 .PHONY: clean
 clean:
-	rm -f *.elf *.bin $(OBJS) $(DEFAULTAPP_OBJS) $(RESET_TEST_OBJS) \
-	$(TESTAPP_OBJS) $(TESTLOADAPP_OBJS)
+	rm -f *.elf *.bin $(OBJS) $(DEFAULTAPP_OBJS) $(LOOPBACKAPP_OBJS) \
+	$(RESET_TEST_OBJS) $(TESTAPP_OBJS) $(TESTLOADAPP_OBJS)
 
diff --git a/hw/application_fpga/apps/loopbackapp/main.c b/hw/application_fpga/apps/loopbackapp/main.c
new file mode 100644
index 0000000..0121d0f
--- /dev/null
+++ b/hw/application_fpga/apps/loopbackapp/main.c
@@ -0,0 +1,143 @@
+// Copyright (C) 2022, 2023 - Tillitis AB
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <tkey/assert.h>
+#include <tkey/io.h>
+#include <tkey/led.h>
+#include <tkey/lib.h>
+
+#define BUFSIZE 256
+#define HEADER_SIZE 2
+#define HID_PACKET_SIZE 64
+#define MAX_PAYLOAD_SIZE 64
+#define SLEEPTIME 100000
+
+void sleep(uint32_t n)
+{
+	for (volatile int i = 0; i < n; i++)
+		;
+}
+
+int main(void)
+{
+	uint8_t available = 0;
+	uint8_t cmdbuf[BUFSIZE] = {0};
+	enum ioend endpoint = IO_NONE;
+	bool waiting_for_more_data = false;
+	uint8_t dest_endpoint = IO_NONE;
+	uint8_t payload_length = 0;
+	uint8_t payload_left = 0;
+	uint8_t payloadbuf[MAX_PAYLOAD_SIZE] = {0};
+	uint8_t first_packet_len = HID_PACKET_SIZE - HEADER_SIZE;
+	uint8_t endpoints = IO_DEBUG;
+	led_set(LED_BLUE);
+
+	// Give time to CH552 to settle USB enumeration at power on
+	sleep(SLEEPTIME * 5);
+
+	// Setup available endpoints
+	endpoints |= IO_CDC | IO_FIDO;
+	config_endpoints(endpoints);
+
+	while (1) {
+		// Wait for data
+		if (readselect(endpoints, &endpoint, &available) != 0) {
+			assert(1 == 2);
+		}
+
+		switch (endpoint) {
+		case IO_CDC:
+			cmdbuf[0] = IO_CDC;
+			cmdbuf[1] = available;
+			if (read(IO_CDC, cmdbuf + 2, BUFSIZE - 2, available) <
+			    0) {
+				assert(1 == 2);
+			}
+			write(IO_DEBUG, cmdbuf, available + 2);
+			memset(cmdbuf, 0, BUFSIZE);
+			break;
+
+		case IO_FIDO:
+			cmdbuf[0] = IO_FIDO;
+			cmdbuf[1] = available;
+			if (read(IO_FIDO, cmdbuf + 2, BUFSIZE - 2, available) <
+			    0) {
+				assert(1 == 2);
+			}
+			write(IO_DEBUG, cmdbuf, available + 2);
+			memset(cmdbuf, 0, BUFSIZE);
+			break;
+
+		case IO_CCID:
+			cmdbuf[0] = IO_CCID;
+			cmdbuf[1] = available;
+			if (read(IO_CCID, cmdbuf + 2, BUFSIZE - 2, available) <
+			    0) {
+				assert(1 == 2);
+			}
+			write(IO_DEBUG, cmdbuf, available + 2);
+			memset(cmdbuf, 0, BUFSIZE);
+			break;
+
+		case IO_DEBUG:
+			if (available != HID_PACKET_SIZE) {
+				led_set(LED_RED);
+				while (1)
+					;
+			}
+
+			if (read(IO_DEBUG, cmdbuf, BUFSIZE, available) < 0) {
+				assert(1 == 2);
+			}
+
+			if (!waiting_for_more_data) {
+				dest_endpoint = cmdbuf[0];
+				payload_length = cmdbuf[1];
+
+				// Check that destination endpoint is ok
+				if (dest_endpoint != IO_CDC &&
+				    dest_endpoint != IO_FIDO &&
+				    dest_endpoint != IO_CCID) {
+					led_set(LED_RED);
+					while (1)
+						;
+				}
+
+				// Check payload size
+				if (payload_length > MAX_PAYLOAD_SIZE) {
+					led_set(LED_RED);
+					while (1)
+						;
+				}
+
+				// Complete payload fits in this packet
+				if (payload_length <= first_packet_len) {
+					write(dest_endpoint, cmdbuf + 2,
+					      payload_length);
+					memset(cmdbuf, 0, BUFSIZE);
+				} else { // More payload will come in next
+					 // packet
+					memcpy(payloadbuf, cmdbuf + 2,
+					       first_packet_len);
+					payload_left =
+					    payload_length - first_packet_len;
+					waiting_for_more_data = true;
+				}
+			} else {
+				memcpy(payloadbuf + first_packet_len, cmdbuf,
+				       payload_left);
+				write(dest_endpoint, payloadbuf,
+				      payload_length);
+				memset(payloadbuf, 0, MAX_PAYLOAD_SIZE);
+				memset(cmdbuf, 0, BUFSIZE);
+				waiting_for_more_data = false;
+			}
+			break;
+
+		default:
+			break;
+		}
+	}
+}