2 files changed, 16 insertions, 6 deletions
diff --git a/libmaple/include/libmaple/usb_cdcacm.h b/libmaple/include/libmaple/usb_cdcacm.h
index 5a2779e..5fe832c 100644
--- a/libmaple/include/libmaple/usb_cdcacm.h
+++ b/libmaple/include/libmaple/usb_cdcacm.h
@@ -127,6 +127,7 @@ uint32 usb_cdcacm_peek(uint8* buf, uint32 len);
 
 uint32 usb_cdcacm_data_available(void); /* in RX buffer */
 uint16 usb_cdcacm_get_pending(void);
+uint8 usb_cdcacm_is_transmitting(void);
 
 uint8 usb_cdcacm_get_dtr(void);
 uint8 usb_cdcacm_get_rts(void);
diff --git a/libmaple/usb/stm32f1/usb_cdcacm.c b/libmaple/usb/stm32f1/usb_cdcacm.c
index cdcba9c..3f3a493 100644
--- a/libmaple/usb/stm32f1/usb_cdcacm.c
+++ b/libmaple/usb/stm32f1/usb_cdcacm.c
@@ -267,6 +267,8 @@ static volatile uint8 vcomBufferRx[USB_CDCACM_RX_EPSIZE];
 static volatile uint32 rx_offset = 0;
 /* Number of bytes left to transmit */
 static volatile uint32 n_unsent_bytes = 0;
+/* Are we currently sending an IN packet? */
+static volatile uint8 transmitting = 0;
 /* Number of unread bytes */
 static volatile uint32 n_unread_bytes = 0;
 
@@ -407,6 +409,13 @@ uint32 usb_cdcacm_tx(const uint8* buf, uint32 len) {
         usb_set_ep_tx_count(USB_CDCACM_TX_ENDP, len);
         n_unsent_bytes = len;
         usb_set_ep_tx_stat(USB_CDCACM_TX_ENDP, USB_EP_STAT_TX_VALID);
+        transmitting = 1;
+    } else {
+        usb_set_ep_tx_count(USB_CDCACM_TX_ENDP, 0);
+        usb_set_ep_tx_stat(USB_CDCACM_TX_ENDP, USB_EP_STAT_TX_VALID);
+        // actually block here waiting for interrupt, even though we sent 0 bytes
+        n_unsent_bytes = 0;
+        transmitting = 1;
     }
 
     return len;
@@ -416,7 +425,11 @@ uint32 usb_cdcacm_data_available(void) {
     return n_unread_bytes;
 }
 
-uint16 usb_cdcacm_get_pending() {
+uint8 usb_cdcacm_is_transmitting(void) {
+    return transmitting;
+}
+
+uint16 usb_cdcacm_get_pending(void) {
     return n_unsent_bytes;
 }
 
@@ -497,12 +510,8 @@ int usb_cdcacm_get_n_data_bits(void) {
  */
 
 static void vcomDataTxCb(void) {
-    /* The following assumes that all of the bytes we copied during
-     * the last call to usb_cdcacm_tx were sent during the IN
-     * transaction (this seems to be the case). */
-    /* TODO find out why this is broken:
-     * n_unsent_bytes = usb_get_ep_tx_count(USB_CDCACM_TX_ENDP); */
     n_unsent_bytes = 0;
+    transmitting = 0;
 }
 
 static void vcomDataRxCb(void) {