diff --git a/legacy/emulator/emulator.h b/legacy/emulator/emulator.h
index caa9ec140..bda59207c 100644
--- a/legacy/emulator/emulator.h
+++ b/legacy/emulator/emulator.h
@@ -30,7 +30,8 @@ void emulatorPoll(void);
 void emulatorRandom(void *buffer, size_t size);
 
 void emulatorSocketInit(void);
-size_t emulatorSocketRead(int *iface, void *buffer, size_t size);
+size_t emulatorSocketRead(int *iface, void *buffer, size_t size,
+                          int timeout_ms);
 size_t emulatorSocketWrite(int iface, const void *buffer, size_t size);
 
 #endif
diff --git a/legacy/emulator/udp.c b/legacy/emulator/udp.c
index 2c60be6a2..e74ef0ee8 100644
--- a/legacy/emulator/udp.c
+++ b/legacy/emulator/udp.c
@@ -19,6 +19,7 @@
 
 #include <arpa/inet.h>
 #include <errno.h>
+#include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -35,6 +36,8 @@ struct usb_socket {
 static struct usb_socket usb_main;
 static struct usb_socket usb_debug;
 
+static struct pollfd usb_fds[2];
+
 static int socket_setup(int port) {
   int fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
   if (fd < 0) {
@@ -96,23 +99,26 @@ static size_t socket_read(struct usb_socket *sock, void *buffer, size_t size) {
 void emulatorSocketInit(void) {
   usb_main.fd = socket_setup(TREZOR_UDP_PORT);
   usb_main.fromlen = 0;
+  usb_fds[0].fd = usb_main.fd;
+  usb_fds[0].events = POLLIN;
+
   usb_debug.fd = socket_setup(TREZOR_UDP_PORT + 1);
   usb_debug.fromlen = 0;
+  usb_fds[1].fd = usb_debug.fd;
+  usb_fds[1].events = POLLIN;
 }
 
-size_t emulatorSocketRead(int *iface, void *buffer, size_t size) {
-  size_t n = socket_read(&usb_main, buffer, size);
-  if (n > 0) {
-    *iface = 0;
-    return n;
-  }
-
-  n = socket_read(&usb_debug, buffer, size);
-  if (n > 0) {
-    *iface = 1;
-    return n;
+size_t emulatorSocketRead(int *iface, void *buffer, size_t size,
+                          int timeout_ms) {
+  if (poll(usb_fds, 2, timeout_ms) > 0) {
+    if (usb_fds[0].revents & POLLIN) {
+      *iface = 0;
+      return socket_read(&usb_main, buffer, size);
+    } else if (usb_fds[1].revents & POLLIN) {
+      *iface = 1;
+      return socket_read(&usb_debug, buffer, size);
+    }
   }
-
   return 0;
 }
 
diff --git a/legacy/firmware/.changelog.d/1743.changed b/legacy/firmware/.changelog.d/1743.changed
new file mode 100644
index 000000000..fbda3b491
--- /dev/null
+++ b/legacy/firmware/.changelog.d/1743.changed
@@ -0,0 +1 @@
+Emulator properly waits for IO without busy loop
diff --git a/legacy/firmware/trezor.c b/legacy/firmware/trezor.c
index 278a36f9d..02ecfbd17 100644
--- a/legacy/firmware/trezor.c
+++ b/legacy/firmware/trezor.c
@@ -157,7 +157,11 @@ int main(void) {
   layoutHome();
   usbInit();
   for (;;) {
+#if EMULATOR
+    usbSleep(10);
+#else
     usbPoll();
+#endif
     check_lock_screen();
   }
 
diff --git a/legacy/firmware/udp.c b/legacy/firmware/udp.c
index 7d0a71d2e..4a8918f37 100644
--- a/legacy/firmware/udp.c
+++ b/legacy/firmware/udp.c
@@ -35,43 +35,38 @@ void usbInit(void) { emulatorSocketInit(); }
 #define _ISDBG ('n')
 #endif
 
-void usbPoll(void) {
+void usbSleep(uint32_t millis) {
   emulatorPoll();
 
   static uint8_t buffer[USB_PACKET_SIZE];
 
   int iface = 0;
-  if (emulatorSocketRead(&iface, buffer, sizeof(buffer)) > 0) {
+  if (emulatorSocketRead(&iface, buffer, sizeof(buffer), millis) > 0) {
     if (!tiny) {
-      msg_read_common(_ISDBG, buffer, sizeof(buffer));
+      do {
+        msg_read_common(_ISDBG, buffer, sizeof(buffer));
+      } while (emulatorSocketRead(&iface, buffer, sizeof(buffer), 0) > 0);
     } else {
       msg_read_tiny(buffer, sizeof(buffer));
     }
   }
 
-  const uint8_t *data = msg_out_data();
-  if (data != NULL) {
+  const uint8_t *data;
+  while ((data = msg_out_data()) != NULL) {
     emulatorSocketWrite(0, data, USB_PACKET_SIZE);
   }
 
 #if DEBUG_LINK
-  data = msg_debug_out_data();
-  if (data != NULL) {
+  while ((data = msg_debug_out_data()) != NULL) {
     emulatorSocketWrite(1, data, USB_PACKET_SIZE);
   }
 #endif
 }
 
+void usbPoll(void) { usbSleep(0); }
+
 char usbTiny(char set) {
   char old = tiny;
   tiny = set;
   return old;
 }
-
-void usbSleep(uint32_t millis) {
-  uint32_t start = timer_ms();
-
-  while ((timer_ms() - start) < millis) {
-    usbPoll();
-  }
-}