Better USB connection detection

main.c

@@ -104,11 +104,11 @@ int main(void) {
   int last_pos = 0;
   uint32_t watchdog_counter = 0;
 
-  while (tick < 5000) {
+  while (tick < 5000 && !usb_connected()) {
     usbd_poll(g_usbd_dev);
   }
 
-  if (!usb_got_reset()) {
+  if (!usb_connected()) {
     fast_reset();
   }
 
@@ -210,7 +210,7 @@ int main(void) {
 
     /* Send replies */
     if ((buf_len = ringbuffer_peek(comm_out_buf, &buf[0], sizeof buf))) {
-      if (usb_write_cdcacm(ACM_COMM, (void *)buf, buf_len, 1)) {
+      if (!usb_connected() || usb_write_cdcacm(ACM_COMM, (void *)buf, buf_len, 1)) {
         ringbuffer_skip(comm_out_buf, buf_len);
       }
     }
@@ -218,7 +218,7 @@ int main(void) {
     /* Send any available data to the NFC CDC */
     if (!ringbuffer_empty(uart_to_usb_buf)) {
       unsigned len = ringbuffer_peek(uart_to_usb_buf, &buf[0], sizeof buf);
-      if (usb_write_cdcacm(ACM_NFC, &buf[0], len, 1)) {
+      if (!usb_connected() || usb_write_cdcacm(ACM_NFC, &buf[0], len, 1)) {
         ringbuffer_skip(uart_to_usb_buf, len);
       }
     }

usb.c

@@ -11,6 +11,9 @@
 
 extern ringbuffer *usb_to_uart_buf, *comm_in_buf;
 
+static void usb_reset_callback(void);
+static void usb_suspend_callback(void);
+
 /* Number of serial devices we want to provide. */
 #define NUM_SERIAL 2
 
@@ -40,7 +43,7 @@ static char const *usb_strings[] = {
     [3 + ACM_NFC] = "RFID",
 };
 
-static int got_reset = 0;
+static int connected = 0;
 
 usbd_device *g_usbd_dev;
 
@@ -176,11 +179,15 @@ static void cdcacm_set_config(usbd_device *usbd_dev, uint16_t wValue) {
 }
 
 void usb_reset_callback(void) {
-  got_reset = 1;
+  connected = 1;
 }
 
-bool usb_got_reset(void) {
-  return got_reset;
+void usb_suspend_callback(void) {
+  connected = 0;
+}
+
+bool usb_connected(void) {
+  return connected;
 }
 
 void usb_setup() {
@@ -337,6 +344,7 @@ void usb_reinit() {
                          usbd_control_buffer, sizeof(usbd_control_buffer));
 
   usbd_register_reset_callback(g_usbd_dev, &usb_reset_callback);
+  usbd_register_suspend_callback(g_usbd_dev, &usb_suspend_callback);
   usbd_register_set_config_callback(g_usbd_dev, cdcacm_set_config);
 }
 

usb.h

@@ -8,7 +8,7 @@ extern usbd_device *g_usbd_dev;
 void usb_setup(void);
 void usb_reinit(void);
 int usb_write_cdcacm(uint8_t acm, void *data, size_t len, int tries);
-bool usb_got_reset(void);
+bool usb_connected(void);
 
 #define ACM_NFC 1
 #define ACM_COMM 0