Implementation of the discussed changes

- remove usbd_edpt_xfer_abort
- rename tu_fifo_change_mode to tu_fifo_set_mode
- remove CFG_TUD_CDC_CLEAR_AT_CONNECTION definition
- remove auto fifo clear at connection event
- add tud_cdc_n_write_clear function

src/class/cdc/cdc_device.c

@@ -207,6 +207,10 @@ uint32_t tud_cdc_n_write_available (uint8_t itf)
   return tu_fifo_remaining(&_cdcd_itf[itf].tx_ff);
 }
 
+bool tud_cdc_n_write_clear (uint8_t itf)
+{
+  return tu_fifo_clear(&_cdcd_itf[itf].tx_ff);
+}
 
 //--------------------------------------------------------------------+
 // USBD Driver API
@@ -229,6 +233,9 @@ void cdcd_init(void)
 
     // config fifo
     tu_fifo_config(&p_cdc->rx_ff, p_cdc->rx_ff_buf, TU_ARRAY_SIZE(p_cdc->rx_ff_buf), 1, false);
+    // tx fifo is set to overwritable at initialization and will be changed to not overwritable
+    // if terminal supports DTR bit. Without DTR we do not know if data is actually polled by terminal.
+    // In this way, the most current data is prioritized.
     tu_fifo_config(&p_cdc->tx_ff, p_cdc->tx_ff_buf, TU_ARRAY_SIZE(p_cdc->tx_ff_buf), 1, true);
 
 #if CFG_FIFO_MUTEX
@@ -384,20 +391,14 @@ bool cdcd_control_request(uint8_t rhport, tusb_control_request_t const * request
       bool const dtr = tu_bit_test(request->wValue, 0);
       bool const rts = tu_bit_test(request->wValue, 1);
 
-#if CFG_TUD_CDC_CLEAR_AT_CONNECTION
-      // DTE connected event (if DTE supports DTR bit)
-      if ( dtr && !tu_bit_test(p_cdc->line_state, 0) )
-      {
-        // Clear not transmitted data
-        usbd_edpt_xfer_abort(rhport, p_cdc->ep_in);
-        tu_fifo_clear(&p_cdc->tx_ff);
-      }
-#endif
+      // TODO if terminal supports DTR we can check for an connection event here and
+      // clear the fifo as well as ongoing transfers with new usbd_edpt_xfer_abort api.
+      // Until then user can self clear the buffer with tud_cdc_n_write_clear in tud_cdc_line_state_cb
 
       p_cdc->line_state = (uint8_t) request->wValue;
 
       // Disable fifo overwriting if DTR bit is set
-      tu_fifo_change_mode(&p_cdc->tx_ff, (dtr?false:true));
+      tu_fifo_set_mode(&p_cdc->tx_ff, !dtr);
 
       TU_LOG2("  Set Control Line State: DTR = %d, RTS = %d\r\n", dtr, rts);
 

src/class/cdc/cdc_device.h

@@ -43,10 +43,6 @@
   #define CFG_TUD_CDC_EP_BUFSIZE    (TUD_OPT_HIGH_SPEED ? 512 : 64)
 #endif
 
-#ifndef CFG_TUD_CDC_CLEAR_AT_CONNECTION
-  #define CFG_TUD_CDC_CLEAR_AT_CONNECTION   0
-#endif
-
 #ifdef __cplusplus
  extern "C" {
 #endif
@@ -106,6 +102,9 @@ uint32_t tud_cdc_n_write_flush     (uint8_t itf);
 // Return the number of bytes (characters) available for writing to TX FIFO buffer in a single n_write operation.
 uint32_t tud_cdc_n_write_available (uint8_t itf);
 
+// Clear the transmit FIFO
+bool tud_cdc_n_write_clear (uint8_t itf);
+
 //--------------------------------------------------------------------+
 // Application API (Single Port)
 //--------------------------------------------------------------------+
@@ -125,6 +124,7 @@ static inline uint32_t tud_cdc_write           (void const* buffer, uint32_t buf
 static inline uint32_t tud_cdc_write_str       (char const* str);
 static inline uint32_t tud_cdc_write_flush     (void);
 static inline uint32_t tud_cdc_write_available (void);
+static inline bool     tud_cdc_write_clear     (void);
 
 //--------------------------------------------------------------------+
 // Application Callback API (weak is optional)
@@ -234,6 +234,11 @@ static inline uint32_t tud_cdc_write_available(void)
   return tud_cdc_n_write_available(0);
 }
 
+static inline bool tud_cdc_write_clear(void)
+{
+  return tud_cdc_n_write_clear(0);
+}
+
 /** @} */
 /** @} */
 

src/common/tusb_fifo.c

@@ -603,9 +603,11 @@ bool tu_fifo_clear(tu_fifo_t *f)
 
     @param[in]  f
                 Pointer to the FIFO buffer to manipulate
+    @param[in]  overwritable
+                Overwritable mode the fifo is set to
 */
 /******************************************************************************/
-bool tu_fifo_change_mode(tu_fifo_t *f, bool overwritable)
+bool tu_fifo_set_mode(tu_fifo_t *f, bool overwritable)
 {
   tu_fifo_lock(f);
 

src/common/tusb_fifo.h

@@ -89,7 +89,7 @@ typedef struct
         .non_used_index_space   = 0xFFFF - 2*_depth-1,                  \
     }
 
-bool tu_fifo_change_mode(tu_fifo_t *f, bool overwritable);
+bool tu_fifo_set_mode(tu_fifo_t *f, bool overwritable);
 bool tu_fifo_clear(tu_fifo_t *f);
 bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_size, bool overwritable);
 

src/device/usbd.c

@@ -1191,33 +1191,6 @@ bool usbd_edpt_xfer(uint8_t rhport, uint8_t ep_addr, uint8_t * buffer, uint16_t
   }
 }
 
-bool usbd_edpt_xfer_abort(uint8_t rhport, uint8_t ep_addr)
-{
-  uint8_t const epnum = tu_edpt_number(ep_addr);
-  uint8_t const dir   = tu_edpt_dir(ep_addr);
-
-  TU_LOG2("  Abort XFER EP %02X ... ", ep_addr);
-
-  // Abort API is optional for DCD
-  if ( dcd_edpt_xfer_abort )
-  {
-    if ( dcd_edpt_xfer_abort(rhport, ep_addr) )
-    {
-      _usbd_dev.ep_status[epnum][dir].busy = false;
-      TU_LOG2("OK\r\n");
-      return true;
-    }else
-    {
-      TU_LOG2("failed\r\n");
-      return false;
-    }
-  }else
-  {
-    TU_LOG2("no DCD support\r\n");
-    return false;
-  }
-}
-
 bool usbd_edpt_busy(uint8_t rhport, uint8_t ep_addr)
 {
   (void) rhport;

src/device/usbd_pvt.h

@@ -70,9 +70,6 @@ void usbd_edpt_close(uint8_t rhport, uint8_t ep_addr);
 // Submit a usb transfer
 bool usbd_edpt_xfer(uint8_t rhport, uint8_t ep_addr, uint8_t * buffer, uint16_t total_bytes);
 
-// Abort a scheduled transfer
-bool usbd_edpt_xfer_abort(uint8_t rhport, uint8_t ep_addr);
-
 // Claim an endpoint before submitting a transfer.
 // If caller does not make any transfer, it must release endpoint for others.
 bool usbd_edpt_claim(uint8_t rhport, uint8_t ep_addr);