grainuum: add functions to drop currently-queued data

These can be used to ignore data that's already in the buffer.

Signed-off-by: Sean Cross <[email protected]>

grainuum-state.c

@@ -212,6 +212,18 @@ static int grainuum_state_send_data(struct GrainuumState *state,
   return 0;
 }
 
+void grainuumDropData(struct GrainuumUSB *usb)
+{
+  usb->state.packet_queued = 0;
+  usb->state.data_out = 0;
+  grainuumWriteQueue(usb, 0, NULL, 0);
+}
+
+int grainuumDataQueued(struct GrainuumUSB *usb)
+{
+  return (usb->state.data_out || usb->state.packet_queued);
+}
+
 int grainuumSendData(struct GrainuumUSB *usb, int epnum,
                      const void *data, int size)
 {

grainuum.h

@@ -446,6 +446,28 @@ int grainuumInitialized(struct GrainuumUSB *usb);
  */
 int grainuumSendData(struct GrainuumUSB *usb, int epnum, const void *data, int size);
 
+/**
+ * @brief   Clears the send buffer, if not empty.
+ * @note    If data has already been queued for the PHY, then
+ *          this will not prevent it from being sent.
+ *          This function is intended to be used to prevent
+ *          grainuumSendData() from returning -EAGAIN.
+ * @param[in] usb     pointer to the @p GrainuumUSB object.
+ * @api
+ */
+void grainuumDropData(struct GrainuumUSB *usb);
+
+/**
+ * @brief   Determines if data is already queued.
+ * @note    If data has been queued, then this will return
+ *          nonzero.  If this returns zero, then you can
+ *          trust grainuumSendData() will succeed.
+ * @param[in] usb     pointer to the @p GrainuumUSB object.
+ * @return            Nonzero if data is already queued.
+ * @api
+ */
+int grainuumDataQueued(struct GrainuumUSB *usb);
+
 /**
  * @brief   Process one received packet through the Grainuum state machine.
  * @note    This feeds USB packets into the state machine.  It should not