2 files changed, 16 insertions, 0 deletions
diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index 681a1b852..ebc408f5a 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -83,6 +83,10 @@ static tud_cdc_configure_fifo_t _cdcd_fifo_cfg;
 
 static bool _prep_out_transaction (cdcd_interface_t* p_cdc) {
   uint8_t const rhport = 0;
+
+  // Skip if usb is not ready yet
+  TU_VERIFY(tud_ready() && p_cdc->ep_out);
+
   uint16_t available = tu_fifo_remaining(&p_cdc->rx_ff);
 
   // Prepare for incoming data but only allow what we can store in the ring buffer.
@@ -116,6 +120,10 @@ bool tud_cdc_configure_fifo(tud_cdc_configure_fifo_t const* cfg) {
   return true;
 }
 
+bool tud_cdc_n_ready(uint8_t itf) {
+  return tud_ready() && _cdcd_itf[itf].ep_in != 0 && _cdcd_itf[itf].ep_out != 0;
+}
+
 bool tud_cdc_n_connected(uint8_t itf) {
   // DTR (bit 0) active  is considered as connected
   return tud_ready() && tu_bit_test(_cdcd_itf[itf].line_state, 0);
diff --git a/src/class/cdc/cdc_device.h b/src/class/cdc/cdc_device.h
index 34670517a..3ad7c8baf 100644
--- a/src/class/cdc/cdc_device.h
+++ b/src/class/cdc/cdc_device.h
@@ -61,6 +61,9 @@ bool tud_cdc_configure_fifo(tud_cdc_configure_fifo_t const* cfg);
 // Application API (Multiple Ports) i.e. CFG_TUD_CDC > 1
 //--------------------------------------------------------------------+
 
+// Check if interface is ready
+bool tud_cdc_n_ready(uint8_t itf);
+
 // Check if terminal is connected to this port
 bool tud_cdc_n_connected(uint8_t itf);
 
@@ -116,6 +119,11 @@ bool tud_cdc_n_write_clear(uint8_t itf);
 //--------------------------------------------------------------------+
 // Application API (Single Port)
 //--------------------------------------------------------------------+
+
+TU_ATTR_ALWAYS_INLINE static inline bool tud_cdc_ready(void) {
+  return tud_cdc_n_ready(0);
+}
+
 TU_ATTR_ALWAYS_INLINE static inline bool tud_cdc_connected(void) {
   return tud_cdc_n_connected(0);
 }