Made Command Flow Control match the actual behavior specified in

the Bluetooth spec (Vol 2, Part E, Section 4.4), old version tended to
collect extra allowed commands over time and eventually lock up.

linux/hci/hci.go

@@ -144,7 +144,7 @@ func (h *HCI) Init() error {
 	}
 	h.skt = skt
 
-	h.chCmdBufs <- make([]byte, 64)
+	h.setAllowedCommands(1)
 
 	go h.sktLoop()
 	if err := h.init(); err != nil {
@@ -407,13 +407,11 @@ func (h *HCI) handleLEAdvertisingReport(b []byte) error {
 
 func (h *HCI) handleCommandComplete(b []byte) error {
 	e := evt.CommandComplete(b)
-	for i := 0; i < int(e.NumHCICommandPackets()); i++ {
-		h.chCmdBufs <- make([]byte, 64)
-	}
+	h.setAllowedCommands(int(e.NumHCICommandPackets()))
 
 	// NOP command, used for flow control purpose [Vol 2, Part E, 4.4]
+	// no handling other than setAllowedCommands needed
 	if e.CommandOpcode() == 0x0000 {
-		h.chCmdBufs = make(chan []byte, 16)
 		return nil
 	}
 	h.muSent.Lock()
@@ -428,9 +426,7 @@ func (h *HCI) handleCommandComplete(b []byte) error {
 
 func (h *HCI) handleCommandStatus(b []byte) error {
 	e := evt.CommandStatus(b)
-	for i := 0; i < int(e.NumHCICommandPackets()); i++ {
-		h.chCmdBufs <- make([]byte, 64)
-	}
+	h.setAllowedCommands(int(e.NumHCICommandPackets()))
 
 	h.muSent.Lock()
 	p, found := h.sent[int(e.CommandOpcode())]
@@ -542,3 +538,16 @@ func (h *HCI) handleLELongTermKeyRequest(b []byte) error {
 		ConnectionHandle: e.ConnectionHandle(),
 	}, nil)
 }
+
+func (h *HCI) setAllowedCommands(n int) {
+
+	//hard-coded limit to command queue depth
+	if n > 16 {
+		n = 16
+	}
+
+	for len(h.chCmdBufs) < n {
+		h.chCmdBufs <- make([]byte, 64)
+	}
+}
+